/******************************************************************************
 * $Id: ogrsf_frmts.dox,v 1.22 2004/11/21 22:08:49 fwarmerdam Exp $
 *
 * Project:  OpenGIS Simple Features Reference Implementation
 * Purpose:  Documentation for ogrsf_frmts.h classes.
 * Author:   Frank Warmerdam, warmerda@home.com
 *
 ******************************************************************************
 * Copyright (c) 1999,  Les Technologies SoftMap Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 ******************************************************************************
 *
 * $Log: ogrsf_frmts.dox,v $
 * Revision 1.22  2004/11/21 22:08:49  fwarmerdam
 * added Release() and DestroyDataSource() methods on OGRDataSource
 *
 * Revision 1.21  2004/11/08 18:52:11  fwarmerdam
 * Added CreateField docs.
 *
 * Revision 1.20  2003/10/17 17:45:41  danmo
 * Added documentation on GetLayerByName() method and OGR_DS_GetLayerByName() function. (Normand Savard)
 *
 * Revision 1.19  2003/10/09 15:28:07  warmerda
 * added OGRLayer::DeleteFeature() support
 *
 * Revision 1.18  2003/08/04 17:22:35  warmerda
 * avoid comments in code blocks
 *
 * Revision 1.17  2003/05/28 19:17:31  warmerda
 * fixup stuff for docs
 *
 * Revision 1.16  2003/04/22 19:35:16  warmerda
 * Added SyncToDisk
 *
 * Revision 1.15  2003/04/03 23:39:11  danmo
 * Small updates to C API docs (Normand S.)
 *
 * Revision 1.14  2003/03/31 15:55:42  danmo
 * Added C API function docs
 *
 * Revision 1.13  2003/03/21 02:58:22  warmerda
 * added ref count stuff
 *
 * Revision 1.12  2003/03/03 05:06:08  warmerda
 * added support for DeleteDataSource and DeleteLayer
 *
 * Revision 1.11  2003/02/08 00:37:23  warmerda
 * added CreateLayer() documentation
 *
 * Revision 1.10  2002/09/26 18:16:02  warmerda
 * added missing methods, and C API mentions
 *
 * Revision 1.9  2002/04/24 02:49:23  warmerda
 * Update notes on GetExtent() when no spatial features.
 *
 * Revision 1.8  2002/03/27 21:24:55  warmerda
 * updates notes on GetFeature()
 *
 * Revision 1.7  2001/10/02 14:24:24  warmerda
 * added SetAttributeFilter docs
 *
 * Revision 1.6  2001/03/15 04:01:43  danmo
 * Added OGRLayer::GetExtent()
 *
 * Revision 1.5  1999/10/13 13:19:22  warmerda
 * Fixed CreateFeature() documentation.
 *
 * Revision 1.4  1999/07/27 00:50:34  warmerda
 * added a number of OGRLayer methods
 *
 * Revision 1.3  1999/07/08 20:23:07  warmerda
 * Added help for GetFeatureCount(), and spatial filtering.
 *
 * Revision 1.2  1999/07/06 20:37:32  warmerda
 * Added header.
 *
 */

/************************************************************************/
/*                         OGRSFDriverRegistrar                         */
/************************************************************************/

/**
 
  \fn OGRDataSource *OGRSFDriverRegistrar::Open( const char *pszName, int bUpdate = FALSE, OGRSFDriver **ppoDriver=NULL);

  Open a file / data source with one of the registered drivers.

  This method loops through all the drivers registered with the driver
  manager trying each until one succeeds with the given data source.  This
  method is static.  Applications don't normally need to use any other
  OGRSFDriverRegistrar methods directly, not do they normally need to have
  a pointer to an OGRSFDriverRegistrar instance.

  If this method fails, CPLGetLastErrorMsg() can be used to check if there
  is an error message explaining why.

  This method is the same as the C function OGROpen().

  @param pszName the name of the file, or data source to open.
  @param bUpdate FALSE for read-only access (the default) or TRUE for 
         read-write access.
  @param ppoDriver if non-NULL, this argument will be updated with a 
         pointer to the driver which was used to open the data source.

  @return NULL on error or if the pass name is not supported by this driver,
  otherwise a pointer to an OGRDataSource.  This OGRDataSource should be
  closed by deleting the object when it is no longer needed.

  <b>Example:</b>

  <pre>
    OGRDataSource	*poDS;

    poDS = OGRSFDriverRegistrar::Open( "polygon.shp" );
    if( poDS == NULL )
    {
        return;
    }

    ... use the data source ...

    delete poDS;
  </pre>

*/


/**
 
  \fn OGRDataSourceH OGROpen( const char *pszName, int bUpdate,
                        OGRSFDriverH *pahDriverList );

  Open a file / data source with one of the registered drivers.

  This function loops through all the drivers registered with the driver
  manager trying each until one succeeds with the given data source.  This
  function is static.  Applications don't normally need to use any other
  OGRSFDriverRegistrar function, not do they normally need to have
  a pointer to an OGRSFDriverRegistrar instance.

  If this function fails, CPLGetLastErrorMsg() can be used to check if there
  is an error message explaining why.

  This function is the same as the C++ method OGRSFDriverRegistrar::Open().

  @param pszName the name of the file, or data source to open.
  @param bUpdate FALSE for read-only access (the default) or TRUE for 
         read-write access.
  @param pahDriverList if non-NULL, this argument will be updated with a 
         pointer to the driver which was used to open the data source.

  @return NULL on error or if the pass name is not supported by this driver,
  otherwise an handle to an OGRDataSource.  This OGRDataSource should be
  closed by deleting the object when it is no longer needed.

  <b>Example:</b>

  <pre>
    OGRDataSourceH	*hDS;
    OGRSFDriverH        *pahDriver;

    hDS = OGROpen( "polygon.shp", 0, pahDriver );
    if( hDS == NULL )
    {
        return;
    }

    ... use the data source ...

    delete hDS;
  </pre>

*/

/**
  \fn OGRSFDriverRegistrar *OGRSFDriverRegistrar::GetRegistrar();

  Return the driver manager, creating one if none exist. 

  @return the driver manager.

*/

/** 
  \fn void OGRSFDriverRegistrar::RegisterDriver( OGRSFDriver * poDriver );
  
  Add a driver to the list of registered drivers.

  If the passed driver is already registered (based on pointer comparison) 
  then the driver isn't registered.  New drivers are added at the end of
  the list of registered drivers.

  This method is the same as the C function OGRRegisterDriver().

  @param poDriver the driver to add.

*/


/** 
  \fn void OGRRegisterDriver( OGRSFDriverH hDriver );
  
  Add a driver to the list of registered drivers.

  If the passed driver is already registered (based on handle comparison) 
  then the driver isn't registered.  New drivers are added at the end of
  the list of registered drivers.

  This function is the same as the C++ method 
  OGRSFDriverRegistrar::RegisterDriver().

  @param hDriver handle to the driver to add.

*/

/**

  \fn int OGRSFDriverRegistrar::GetDriverCount();

  Fetch the number of registered drivers.

  This method is the same as the C function OGRGetDriverCount().

  @return the drivers count.

*/

/**

  \fn int OGRGetDriverCount();

  Fetch the number of registered drivers.

  This function is the same as the C++ method 
  OGRSFDriverRegistrar::GetDriverCount().

  @return the drivers count.

*/

/**
 
  \fn OGRSFDriver *OGRSFDriverRegistrar::GetDriver( int iDriver );

  Fetch the indicated driver.

  This method is the same as the C function OGRGetDriver().

  @param iDriver the driver index, from 0 to GetDriverCount()-1.

  @return the driver, or NULL if iDriver is out of range.

*/

/**
 
  \fn OGRSFDriverH OGRGetDriver( int iDriver );

  Fetch the indicated driver.

  This function is the same as the C++ method 
  OGRSFDriverRegistrar::GetDriver().

  @param iDriver the driver index, from 0 to GetDriverCount()-1.

  @return handle to the driver, or NULL if iDriver is out of range.

*/

/**

  \fn int OGRRegisterAll();

  Register all drivers.

*/

/************************************************************************/
/*                             OGRSFDriver                              */
/************************************************************************/


/** 

  \fn const char *OGRSFDriver::GetName();

  Fetch name of driver (file format).  This name should be relatively short
  (10-40 characters), and should reflect the underlying file format.  For
  instance "ESRI Shapefile".

  This method is the same as the C function OGR_Dr_GetName().

  @return driver name.  This is an internal string and should not be modified
  or freed. 
*/


/** 

  \fn const char *OGR_Dr_GetName( OGRSFDriverH hDriver );

  Fetch name of driver (file format).  This name should be relatively short
  (10-40 characters), and should reflect the underlying file format.  For
  instance "ESRI Shapefile".

  This function is the same as the C++ method OGRSFDriver::GetName().

  @param hDriver handle to the the driver to get the name from.
  @return driver name.  This is an internal string and should not be modified
  or freed. 
*/

/**

  \fn OGRDataSource *OGRSFDriver::Open( const char *pszName, int bUpdate );

  Attempt to open file with this driver. 

  This method is what OGRSFDriverRegistrar uses to implement its Open() 
  method.
  See it for more details.

  This method is the same as the C function OGR_Dr_Open().

  @param pszName the name of the file, or data source to try and open.
  @param bUpdate TRUE if update access is required, otherwise FALSE (the
  default).

  @return NULL on error or if the pass name is not supported by this driver,
  otherwise a pointer to an OGRDataSource.  This OGRDataSource should be
  closed by deleting the object when it is no longer needed.

*/


/**

  \fn OGRDataSourceH OGR_Dr_Open( OGRSFDriverH hDriver, const char *pszName, 
                            int bUpdate );

  Attempt to open file with this driver. 

  This function is the same as the C++ method OGRSFDriver::Open().

  @param hDriver handle to the driver that is used to open file.
  @param pszName the name of the file, or data source to try and open.
  @param bUpdate TRUE if update access is required, otherwise FALSE (the
  default).

  @return NULL on error or if the pass name is not supported by this driver,
  otherwise an handle to an OGRDataSource.  This OGRDataSource should be
  closed by deleting the object when it is no longer needed.

*/

/**
 \fn int OGRSFDriver::TestCapability( const char *pszCapability );

 Test if capability is available.

 One of the following data source capability names can be passed into this
 method, and a TRUE or FALSE value will be returned indicating whether or not
 the capability is available for this object.

 <ul>
  <li> <b>ODrCCreateDataSource</b>: True if this driver can support creating data sources.<p>
  <li> <b>ODrCDeleteDataSource</b>: True if this driver supports deleting data sources.<p>
 </ul>

 The #define macro forms of the capability names should be used in preference
 to the strings themselves to avoid mispelling.

 This method is the same as the C function OGR_Dr_TestCapability().

 @param pszCapability the capability to test.

 @return TRUE if capability available otherwise FALSE.
*/ 


/**
 \fn int OGR_Dr_TestCapability( OGRSFDriverH hDriver, const char *pszCap );

 Test if capability is available.

 One of the following data source capability names can be passed into this
 function, and a TRUE or FALSE value will be returned indicating whether
 or not the capability is available for this object.

 <ul>
  <li> <b>ODrCCreateDataSource</b>: True if this driver can support creating data sources.<p>
  <li> <b>ODrCDeleteDataSource</b>: True if this driver supports deleting data sources.<p>
 </ul>

 The #define macro forms of the capability names should be used in preference
 to the strings themselves to avoid mispelling.

 This function is the same as the C++ method OGRSFDriver::TestCapability().

 @param hDriver handle to the driver to test the capability against.
 @param pszCap the capability to test.

 @return TRUE if capability available otherwise FALSE.

*/ 

/**
 \fn OGRErr OGRSFDriver::DeleteDataSource( const char *pszDataSource );

 Destroy a datasource.

 Destroy the named datasource.  Normally it would be safest if the
 datasource was not open at the time. 

 Whether this is a supported operation on this driver case be tested
 using TestCapability() on ODrCDeleteDataSource.

 This method is the same as the C function OGR_Dr_DeleteDataSource().

 @param pszDataSource the name of the datasource to delete. 

 @return OGRERR_NONE on success, and OGRERR_UNSUPPORTED_OPERATION if this
 is not supported by this driver. 
*/


/**
 \fn OGRDataSource *OGRSFDriver::CreateDataSource( const char *pszName, 
                                        char ** papszOptions );

 This method attempts to create a new data source based on the passed
 driver.  The papszOptions argument can be used to control driver specific
 creation options.  These options are normally documented in the format
 specific documentation. 

 This method is the same as the C function OGR_Dr_CreateDataSource().

 @param pszName the name for the new data source.
 @param papszOptions a StringList of name=value options.  Options are driver
specific, and driver information can be found at the following url:  
http://gdal.velocet.ca/projects/opengis/ogrhtml/ogr_formats.html 

 @return NULL is returned on failure, or a new OGRDataSource on 
success. 
*/

/** 

  \fn OGRDataSourceH OGR_Dr_CreateDataSource( OGRSFDriverH hDriver,
                                        const char *pszName, 
                                        char ** papszOptions )

 This function attempts to create a new data source based on the passed
 driver.  The papszOptions argument can be used to control driver specific
 creation options.  These options are normally documented in the format
 specific documentation. 

 This function is the same as the C++ method OGRSFDriver::CreateDataSource().

 @param hDriver handle to the driver on which data source creation is
based.
 @param pszName the name for the new data source.
 @param papszOptions a StringList of name=value options.  Options are driver
specific, and driver information can be found at the following url:  
http://gdal.velocet.ca/projects/opengis/ogrhtml/ogr_formats.html 

 @return NULL is returned on failure, or a new OGRDataSource handle on 
success. 
*/

/************************************************************************/
/*                            OGRDataSource                             */
/************************************************************************/

/** 
 \fn const char *OGRDataSource::GetName();

 Returns the name of the data source.  This string should be sufficient to
 open the data source if passed to the same OGRSFDriver that this data
 source was opened with, but it need not be exactly the same string that
 was used to open the data source.  Normally this a filename. 

 This method is the same as the C function OGR_DS_GetName().

 @return pointer to an internal name string which should not be modified
 or freed by the caller.

*/

/** 
 \fn const char *OGR_DS_GetName( OGRDataSourceH hDS );

 Returns the name of the data source.  This string should be sufficient to
 open the data source if passed to the same OGRSFDriver that this data
 source was opened with, but it need not be exactly the same string that
 was used to open the data source.  Normally this a filename. 

 This function is the same as the C++ method OGRDataSource::GetName().

 @param hDS handle to the data source to get the name from.
 @return pointer to an internal name string which should not be modified
 or freed by the caller.

*/

/**
 \fn int OGRDataSource::GetLayerCount();

 Get the number of layers in this data source.

 This method is the same as the C function OGR_DS_GetLayerCount().

 @return layer count.

*/


/**
 \fn int OGR_DS_GetLayerCount( OGRDataSourceH hDS );

 Get the number of layers in this data source.

 This function is the same as the C++ method OGRDataSource::GetLayerCount().

 @param hDS handle to the data source from which to get the number of layers.
 @return layer count.

*/

/**
 \fn OGRLayer *OGRDataSource::GetLayer(int iLayer);

 Fetch a layer by index.  The returned layer remains owned by the 
 OGRDataSource and should not be deleted by the application.

 This method is the same as the C function OGR_DS_GetLayer().

 @param iLayer a layer number between 0 and GetLayerCount()-1.

 @return the layer, or NULL if iLayer is out of range or an error occurs.

*/


/**
 \fn OGRLayerH OGR_DS_GetLayer( OGRDataSourceH hDS, int iLayer );

 Fetch a layer by index.  The returned layer remains owned by the 
 OGRDataSource and should not be deleted by the application.

 This function is the same as the C++ method OGRDataSource::GetLayer().

 @param hDS handle to the data source from which to get the layer.
 @param iLayer a layer number between 0 and OGR_DS_GetLayerCount()-1.

 @return an handle to the layer, or NULL if iLayer is out of range
 or an error occurs.

*/

/**
 \fn OGRLayer *OGRDataSource::GetLayerByName(const char *pszLayerName);

 Fetch a layer by name.  The returned layer remains owned by the 
 OGRDataSource and should not be deleted by the application.

 This method is the same as the C function OGR_DS_GetLayerByName().

 @param pszLayerName the layer name of the layer to fetch.

 @return the layer, or NULL if Layer is not found or an error occurs.

*/


/**
 \fn OGRLayerH OGR_DS_GetLayerByName(OGRDataSourceH hDS, 
                                     const char *pszLayerName );

 Fetch a layer by name.  The returned layer remains owned by the 
 OGRDataSource and should not be deleted by the application.

 This function is the same as the C++ method OGRDataSource::GetLayerByName().

 @param hDS handle to the data source from which to get the layer.
 @param psz Layer the layer name of the layer to fetch.

 @return an handle to the layer, or NULL if the layer is not found
 or an error occurs.

*/

/**
 \fn OGRErr OGRDataSource::DeleteLayer(int iLayer);

 Delete the indicated layer from the datasource.  If this method is supported
 the ODsCDeleteLayer capability will test TRUE on the OGRDataSource.

 This method is the same as the C function OGR_DS_DeleteLayer().

 @param iLayer the index of the layer to delete. 

 @return OGRERR_NONE on success, or OGRERR_UNSUPPORTED_OPERATION if deleting
 layers is not supported for this datasource.

*/

/**
 \fn OGRLayer *OGRDataSource::ExecuteSQL(const char *pszStatement,
				         OGRGeometry *poSpatialFilter, 
				         const char *pszDialect );

 Execute an SQL statement against the data store. 

 The result of an SQL query is either NULL for statements that are in error,
 or that have no results set, or an OGRLayer pointer representing a results
 set from the query.  Note that this OGRLayer is in addition to the layers
 in the data store and must be destroyed with 
 OGRDataSource::ReleaseResultsSet() before the data source is closed 
 (destroyed).  

 This method is the same as the C function OGR_DS_ExecuteSQL().

 For more information on the SQL dialect supported internally by OGR
 review the <a href="ogr_sql.html">OGR SQL</a> document.  Some drivers (ie.
 Oracle and PostGIS) pass the SQL directly through to the underlying RDBMS.

 @param pszStatement the SQL statement to execute. 
 @param poSpatialFilter geometry which represents a spatial filter.
 @param pszDialect allows control of the statement dialect.  By default it 
 is assumed to be "generic" SQL, whatever that is. 

 @return an OGRLayer containing the results of the query.  Deallocate with
 ReleaseResultsSet().

*/


/**
 \fn OGRLayerH OGR_DS_ExecuteSQL( OGRDataSourceH hDS, 
                             const char *pszSQLCommand,
                             OGRGeometryH hSpatialFilter,
                             const char *pszDialect );

 Execute an SQL statement against the data store. 

 The result of an SQL query is either NULL for statements that are in error,
 or that have no results set, or an OGRLayer handle representing a results
 set from the query.  Note that this OGRLayer is in addition to the layers
 in the data store and must be destroyed with 
 OGR_DS_ReleaseResultsSet() before the data source is closed 
 (destroyed).  

 For more information on the SQL dialect supported internally by OGR
 review the <a href="ogr_sql.html">OGR SQL</a> document.  Some drivers (ie.
 Oracle and PostGIS) pass the SQL directly through to the underlying RDBMS.

 This function is the same as the C++ method OGRDataSource::ExecuteSQL();

 @param hDS handle to the data source on which the SQL query is executed.
 @param pszSQLCommand the SQL statement to execute. 
 @param hSpatialFilter handle to a geometry which represents a spatial filter.
 @param pszDialect allows control of the statement dialect.  By default it 
 is assumed to be "generic" SQL, whatever that is. 

 @return an handle to a OGRLayer containing the results of the query.  
 Deallocate with OGR_DS_ReleaseResultsSet().

*/

/**
 \fn void OGRDataSource::ReleaseResultSet(OGRLayer *poResultsSet);

 Release results of ExecuteSQL().

 This method should only be used to deallocate OGRLayers resulting from
 an ExecuteSQL() call on the same OGRDataSource.  Failure to deallocate a
 results set before destroying the OGRDataSource may cause errors. 

 This method is the same as the C function OGR_L_ReleaseResultsSet().

 @param poResultsSet the result of a previous ExecuteSQL() call.

*/ 


/**
 \fn void OGR_DS_ReleaseResultSet( OGRDataSourceH hDS, OGRLayerH hLayer );

 Release results of OGR_DS_ExecuteSQL().

 This function should only be used to deallocate OGRLayers resulting from
 an OGR_DS_ExecuteSQL() call on the same OGRDataSource.  
 Failure to deallocate a results set before destroying the OGRDataSource 
 may cause errors. 

 This function is the same as the C++ method 
 OGRDataSource::ReleaseResultsSet().

 @param hDS an handle to the data source on which was executed an 
 SQL query.
 @param hLayer handle to the result of a previous OGR_DS_ExecuteSQL() call.

*/ 


/**
 \fn int OGRDataSource::TestCapability( const char *pszCapability );

 Test if capability is available.

 One of the following data source capability names can be passed into this
 method, and a TRUE or FALSE value will be returned indicating whether or not
 the capability is available for this object.

 <ul>
  <li> <b>ODsCreateLayer</b>: True if this datasource can create new layers.<p>
 </ul>

 The #define macro forms of the capability names should be used in preference
 to the strings themselves to avoid mispelling.

 This method is the same as the C function OGR_DS_TestCapability().

 @param pszCapability the capability to test.

 @return TRUE if capability available otherwise FALSE.

*/ 


/**
 \fn int OGR_DS_TestCapability( OGRDataSourceH hDS, const char *pszCapability );

 Test if capability is available.

 One of the following data source capability names can be passed into this
 function, and a TRUE or FALSE value will be returned indicating whether 
 or not the capability is available for this object.

 <ul>
  <li> <b>ODsCreateLayer</b>: True if this datasource can create new layers.
  <p>
 </ul>

 The #define macro forms of the capability names should be used in preference
 to the strings themselves to avoid mispelling.

 This function is the same as the C++ method OGRDataSource::TestCapability().

 @param hDS handle to the data source against which to test the capability.
 @param pszCapability the capability to test.

 @return TRUE if capability available otherwise FALSE.

*/ 

/**
 \fn OGRLayer *OGRDataSource::CreateLayer( const char *pszName, 
                                OGRSpatialReference *poSpatialRef = NULL,
                                OGRwkbGeometryType eGType = wkbUnknown,
                                char ** papszOptions = NULL );

This method attempts to create a new layer on the data source with the
indicated name, coordinate system, geometry type.  The papszOptions argument
can be used to control driver specific creation options.  These options are
normally documented in the format specific documentation. 

 @param pszName the name for the new layer.  This should ideally not 
match any existing layer on the datasource.
 @param poSpatialRef the coordinate system to use for the new layer, or NULL if
no coordinate system is available. 
 @param eGType the geometry type for the layer.  Use wkbUnknown if there
are no constraints on the types geometry to be written. 
 @param papszOptions a StringList of name=value options.  Options are driver
specific.

 @return NULL is returned on failure, or a new OGRLayer handle on success. 

<b>Example:</b>

\code
#include "ogrsf_frmts.h" 
#include "cpl_string.h"

...

	OGRLayer *poLayer;
        char     *papszOptions;

	if( !poDS->TestCapability( ODsCreateLayer ) )
        {
	    ...
        }

        papszOptions = CSLSetNameValue( papszOptions, "DIM", "2" );
        poLayer = poDS->CreateLayer( "NewLayer", NULL, wkbUnknown,
				     papszOptions );
        CSLDestroy( papszOptions );

        if( poLayer == NULL )
        {
            ...
        }        
\endcode
*/

/**
 \fn OGRLayerH OGR_DS_CreateLayer( OGRDataSourceH hDS, 
                              const char * pszName,
                              OGRSpatialReferenceH hSpatialRef,
                              OGRwkbGeometryType eType,
                              char ** papszOptions );

This function attempts to create a new layer on the data source with the
indicated name, coordinate system, geometry type.  The papszOptions argument
can be used to control driver specific creation options.  These options are
normally documented in the format specific documentation. 

This function is the same as the C++ method OGRDataSource::CreateLayer().

 @param hDS The dataset handle.
 @param pszName the name for the new layer.  This should ideally not 
match any existing layer on the datasource.
 @param hSpatialRef handle to the coordinate system to use for the new layer,
or NULL if no coordinate system is available. 
 @param eType the geometry type for the layer.  Use wkbUnknown if there
are no constraints on the types geometry to be written. 
 @param papszOptions a StringList of name=value options.  Options are driver
specific, and driver information can be found at the following url:  
http://gdal.velocet.ca/projects/opengis/ogrhtml/ogr_formats.html 

 @return NULL is returned on failure, or a new OGRLayer handle on success. 

<b>Example:</b>

\code
#include "ogrsf_frmts.h" 
#include "cpl_string.h"

...

	OGRLayerH *hLayer;
        char     *papszOptions;

	if( OGR_DS_TestCapability( hDS, ODsCreateLayer ) )
        {
	    ...
        }

        papszOptions = CSLSetNameValue( papszOptions, "DIM", "2" );
        hLayer = OGR_DS_CreateLayer( hDS, "NewLayer", NULL, wkbUnknown,
				     papszOptions );
        CSLDestroy( papszOptions );

        if( hLayer == NULL )
        {
            ...
        }        
\endcode
*/

/**
 \fn int OGRDataSource::Reference();

Increment datasource reference count.

This method is the same as the C function OGR_DS_Reference().

@return the reference count after incrementing.
*/
				         
/**
 \fn int OGRDataSource::Dereference();

Decrement datasource reference count.

This method is the same as the C function OGR_DS_Dereference().

@return the reference count after decrementing.
*/
				         
/**
 \fn int OGRDataSource::GetRefCount() const;

Fetch reference count.

This method is the same as the C function OGR_DS_GetRefCount().

@return the current reference count for the datasource object itself.
*/
				         
/**
 \fn int OGRDataSource::GetSummaryRefCount() const;

Fetch reference count of datasource and all owned layers.

This method is the same as the C function OGR_DS_GetSummaryRefCount().

@return the current summary reference count for the datasource and its layers.
*/

/**
 \fn OGRErr OGRDataSource::Release();

Drop a reference to this datasource, and if the reference count drops to 
zero close (destroy) the datasource.   Internally this actually calls
the OGRSFDriverRegistrary::ReleaseDataSource() method.  This method is
essentially a convenient alias. 

This method is the same as the C function OGRReleaseDataSource().

@return OGRERR_NONE on success or an error code. 
*/

/**
 \fn OGRErr OGRDataSource::SyncToDisk();

Flush pending changes to disk.

This call is intended to force the datasource to flush any pending writes to
disk, and leave the disk file in a consistent state.  It would not normally
have any effect on read-only datasources. 

Some data sources do not implement this method, and will still return 
OGRERR_NONE.  An error is only returned if an error occurs while attempting
to flush to disk.  

The default implementation of this method just calls the SyncToDisk() method
on each of the layers.  Conceptionally, calling SyncToDisk() on a datasource
should include any work that might be accomplished by calling SyncToDisk()
on layers in that data source.

This method is the same as the C function OGR_DS_SyncToDisk().

@return OGRERR_NONE if no error occurs (even if nothing is done) or an
error code.
*/



/************************************************************************/
/*                               OGRLayer                               */
/************************************************************************/

/**
 \fn void OGRLayer::ResetReading();

 Reset feature reading to start on the first feature.  This affects 
 GetNextFeature().

 This method is the same as the C function OGR_L_ResetReading().

*/

/**
 \fn void OGR_L_ResetReading( OGRLayerH hLayer );

 Reset feature reading to start on the first feature.  This affects 
 GetNextFeature().

 This function is the same as the C++ method OGRLayer::ResetReading().

 @param hLayer handle to the layer on which features are read.

*/

/**
 \fn OGRFeature *OGRLayer::GetNextFeature();

 Fetch the next available feature from this layer.  The returned feature
 becomes the responsiblity of the caller to delete.  It is critical that
 all features associated with an OGRLayer (more specifically an 
 OGRFeatureDefn) be deleted before that layer/datasource is deleted.

 Only features matching the current spatial filter (set with 
 SetSpatialFilter()) will be returned.  

 This method implements sequential access to the features of a layer.  The
 ResetReading() method can be used to start at the beginning again.  Random
 reading, writing and spatial filtering will be added to the OGRLayer in 
 the future.

 This method is the same as the C function OGR_L_GetNextFeature().

 @return a feature, or NULL if no more features are available. 

*/


/**
 \fn OGRFeatureH OGR_L_GetNextFeature( OGRLayerH hLayer );

 Fetch the next available feature from this layer.  The returned feature
 becomes the responsiblity of the caller to delete.  It is critical that
 all features associated with an OGRLayer (more specifically an 
 OGRFeatureDefn) be deleted before that layer/datasource is deleted.

 Only features matching the current spatial filter (set with 
 SetSpatialFilter()) will be returned.  

 This function implements sequential access to the features of a layer.
 The OGR_L_ResetReading() function can be used to start at the beginning 
 again.  Random reading, writing and spatial filtering will be added to
 the OGRLayer in the future.

 This function is the same as the C++ method OGRLayer::GetNextFeature().

 @param hLayer handle to the layer from which feature are read.
 @return an handle to a feature, or NULL if no more features are available. 

*/

/**

 \fn int OGRLayer::GetFeatureCount( int bForce = TRUE );

 Fetch the feature count in this layer. 

 Returns the number of features in the layer.  For dynamic databases the
 count may not be exact.  If bForce is FALSE, and it would be expensive
 to establish the feature count a value of -1 may be returned indicating
 that the count isn't know.  If bForce is TRUE some implementations will
 actually scan the entire layer once to count objects. 

 The returned count takes the spatial filter into account. 

 This method is the same as the C function OGR_L_GetFeatureCount().

 @param bForce Flag indicating whether the count should be computed even
 if it is expensive.

 @return feature count, -1 if count not known. 

*/

/**
 \fnint OGR_L_GetFeatureCount( OGRLayerH hLayer, int bForce );

 Fetch the feature count in this layer. 

 Returns the number of features in the layer.  For dynamic databases the
 count may not be exact.  If bForce is FALSE, and it would be expensive
 to establish the feature count a value of -1 may be returned indicating
 that the count isn't know.  If bForce is TRUE some implementations will
 actually scan the entire layer once to count objects. 

 The returned count takes the spatial filter into account. 

 This function is the same as the CPP OGRLayer::GetFeatureCount().

 @param hLayer handle to the layer that owned the features.
 @param bForce Flag indicating whether the count should be computed even
 if it is expensive.

 @return feature count, -1 if count not known. 

*/

/**

 \fn OGRErr OGRLayer::GetExtent( OGREnvelope *psExtent, int bForce = TRUE );

 Fetch the extent of this layer.

 Returns the extent (MBR) of the data in the layer.  If bForce is FALSE,
 and it would be expensive to establish the extent then OGRERR_FAILURE
 will be returned indicating that the extent isn't know.  If bForce is 
 TRUE then some implementations will actually scan the entire layer once
 to compute the MBR of all the features in the layer.

 The returned extent does not take the spatial filter into account.  If
 a spatial filter was previously set then it should be ignored but some
 implementations may be unable to do that, so it is safer to call 
 GetExtent() without setting a spatial filter.

 Layers without any geometry may return OGRERR_FAILURE just indicating that
 no meaningful extents could be collected.

 This method is the same as the C function OGR_L_GetExtent().

 @param psExtent the structure in which the extent value will be returned.
 @param bForce Flag indicating whether the extent should be computed even
 if it is expensive.

 @return OGRERR_NONE on success, OGRERR_FAILURE if extent not known. 

*/


/**

 \fn OGRErr OGR_L_GetExtent( OGRLayerH hLayer, OGREnvelope *psExtent, int bForce);

 Fetch the extent of this layer.

 Returns the extent (MBR) of the data in the layer.  If bForce is FALSE,
 and it would be expensive to establish the extent then OGRERR_FAILURE
 will be returned indicating that the extent isn't know.  If bForce is 
 TRUE then some implementations will actually scan the entire layer once
 to compute the MBR of all the features in the layer.

 The returned extent does not take the spatial filter into account.  If
 a spatial filter was previously set then it should be ignored but some
 implementations may be unable to do that, so it is safer to call 
 OGR_L_GetExtent() without setting a spatial filter.

 Layers without any geometry may return OGRERR_FAILURE just indicating that
 no meaningful extents could be collected.

 This function is the same as the C++ method OGRLayer::GetExtent().

 @param hLayer handle to the layer from which to get extent.
 @param psExtent the structure in which the extent value will be returned.
 @param bForce Flag indicating whether the extent should be computed even
 if it is expensive.

 @return OGRERR_NONE on success, OGRERR_FAILURE if extent not known. 

*/

/** 
 \fn void OGRLayer::SetSpatialFilter( OGRGeometry * poFilter );

 Set a new spatial filter. 

 This method set the geometry to be used as a spatial filter when 
 fetching features via the GetNextFeature() method.  Only features that
 geometrically intersect the filter geometry will be returned.  

 Currently this test is may be inaccurately implemented, but it is
 guaranteed that all features who's envelope (as returned by
 OGRGeometry::getEnvelope()) overlaps the envelope of the spatial filter
 will be returned.  This can result in more shapes being returned that 
 should strictly be the case. 

 This method makes an internal copy of the passed geometry.  The 
 passed geometry remains the responsibility of the caller, and may 
 be safely destroyed. 

 For the time being the passed filter geometry should be in the same
 SRS as the layer (as returned by OGRLayer::GetSpatialRef()).  In the
 future this may be generalized. 

 This method is the same as the C function OGR_L_SetSpatialFilter().

 @param poFilter the geometry to use as a filtering region.  NULL may
 be passed indicating that the current spatial filter should be cleared,
 but no new one instituted.
 
 */

/** 
 \fn void OGR_L_SetSpatialFilter( OGRLayerH hLayer, OGRGeometryH hGeom );

 Set a new spatial filter. 

 This function set the geometry to be used as a spatial filter when 
 fetching features via the OGR_L_GetNextFeature() function.  Only 
 features that geometrically intersect the filter geometry will be 
 returned.  

 Currently this test is may be inaccurately implemented, but it is
 guaranteed that all features who's envelope (as returned by
 OGR_G_GetEnvelope()) overlaps the envelope of the spatial filter
 will be returned.  This can result in more shapes being returned that 
 should strictly be the case. 

 This function makes an internal copy of the passed geometry.  The 
 passed geometry remains the responsibility of the caller, and may 
 be safely destroyed. 

 For the time being the passed filter geometry should be in the same
 SRS as the layer (as returned by OGR_L_GetSpatialRef()).  In the
 future this may be generalized. 

 This function is the same as the C++ method OGRLayer::SetSpatialFilter.

 @param hLayer handle to the layer on which to set the spatial filter.
 @param hGeom handle to the geometry to use as a filtering region.  NULL may
 be passed indicating that the current spatial filter should be cleared,
 but no new one instituted.
 
 */

/**
 \fn OGRGeometry *OGRLayer::GetSpatialFilter();

 This method returns the current spatial filter for this layer. 

 The returned pointer is to an internally owned object, and should not
 be altered or deleted by the caller.  

 This method is the same as the C function OGR_L_GetSpatialFilter().

 @return spatial filter geometry.
 
 */


/**
 \fn OGRGeometryH OGR_L_GetSpatialFilter( OGRLayerH hLayer );

 This function returns the current spatial filter for this layer. 

 The returned pointer is to an internally owned object, and should not
 be altered or deleted by the caller.  

 This function is the same as the C++ method OGRLayer::GetSpatialFilter().

 @param hLayer handle to the layer to get the spatial filter from.
 @return an handle to the spatial filter geometry.
 
 */

/** 
 \fn void OGRLayer::SetAttributeFilter( const char *pszQuery );

 Set a new attribute query.

 This method sets the attribute query string to be used when 
 fetching features via the GetNextFeature() method.  Only features for which
 the query evaluates as true will be returned.

 The query string should be in the format of an SQL WHERE clause.  For
 instance "population > 1000000 and population < 5000000" where population
 is an attribute in the layer.  The query format is a restricted form of SQL
 WHERE clause as defined "eq_format=restricted_where" about half way through
 this document:

   http://ogdi.sourceforge.net/prop/6.2.CapabilitiesMetadata.html

 Note that installing a query string will generally result in resetting
 the current reading position (ala ResetReading()).  

 This method is the same as the C function OGR_L_SetAttributeFilter().

 @param pszQuery query in restricted SQL WHERE format, or NULL to clear the
 current query.

 @return OGRERR_NONE if successfully installed, or an error code if the 
 query expression is in error, or some other failure occurs. 
 
 */

/** 
 \fn OGRErr OGR_L_SetAttributeFilter(OGRLayerH hLayer, const char *pszQuery);

 Set a new attribute query.

 This function sets the attribute query string to be used when 
 fetching features via the OGR_L_GetNextFeature() function.
 Only features for which the query evaluates as true will be returned.

 The query string should be in the format of an SQL WHERE clause.  For
 instance "population > 1000000 and population < 5000000" where population
 is an attribute in the layer.  The query format is a restricted form of SQL
 WHERE clause as defined "eq_format=restricted_where" about half way through
 this document:

   http://ogdi.sourceforge.net/prop/6.2.CapabilitiesMetadata.html

 Note that installing a query string will generally result in resetting
 the current reading position (ala OGR_L_ResetReading()).  

 This function is the same as the C++ method OGRLayer::SetAttributeFilter().

 @param hLayer handle to the layer on which attribute query will be executed.
 @param pszQuery query in restricted SQL WHERE format, or NULL to clear the
 current query.

 @return OGRERR_NONE if successfully installed, or an error code if the 
 query expression is in error, or some other failure occurs. 
 
 */

/** 
 \fn OGRFeatureDefn *OGRLayer::GetLayerDefn();

 Fetch the schema information for this layer.

 The returned OGRFeatureDefn is owned by the OGRLayer, and should not be
 modified or freed by the application.  It encapsulates the attribute schema
 of the features of the layer. 

 This method is the same as the C function OGR_L_GetLayerDefn().

 @return feature definition.

*/

/** 
 \fn OGRFeatureDefnH OGR_L_GetLayerDefn( OGRLayerH hLayer );

 Fetch the schema information for this layer.

 The returned handle to the OGRFeatureDefn is owned by the OGRLayer,
 and should not be modified or freed by the application.  It encapsulates
 the attribute schema of the features of the layer. 

 This function is the same as the C++ method OGRLayer::GetLayerDefn().

 @param hLayer handle to the layer to get the schema information.
 @return an handle to the feature definition.

*/

/**

 \fn OGRSpatialReference *OGRLayer::GetSpatialRef();

 Fetch the spatial reference system for this layer. 

 The returned object is owned by the OGRLayer and should not be modified
 or freed by the application.  

 This method is the same as the C function OGR_L_GetSpatialRef().

 @return spatial reference, or NULL if there isn't one.

*/


/**

 \fn OGRSpatialReferenceH OGR_L_GetSpatialRef( OGRLayerH hLayer );

 Fetch the spatial reference system for this layer. 

 The returned object is owned by the OGRLayer and should not be modified
 or freed by the application.  

 This function is the same as the C++ method OGRLayer::GetSpatialRef().

 @param hLayer handle to the layer to get the spatial reference from.
 @return spatial reference, or NULL if there isn't one.

*/

/**

 \fn OGRFeature *OGRLayer::GetFeature( long nFID );

 Fetch a feature by it's identifier.

 This function will attempt to read the identified feature.  The nFID
 value cannot be OGRNullFID.  Success or failure of this operation is
 unaffected by the spatial or attribute filters.

 If this method returns a non-NULL feature, it is guaranteed that it's 
 feature id (OGRFeature::GetFID()) will be the same as nFID.

 Use OGRLayer::TestCapability(OLCRandomRead) to establish if this layer
 supports efficient random access reading via GetFeature(); however, the
 call should always work if the feature exists as a fallback implementation
 just scans all the features in the layer looking for the desired feature.
 
 Sequential reads are generally considered interrupted by a GetFeature() call.

 This method is the same as the C function OGR_L_GetFeature().

 @param nFID the feature id of the feature to read. 

 @return a feature now owned by the caller, or NULL on failure. 

*/


/**

 \fn OGRFeatureH OGR_L_GetFeature( OGRLayerH hLayer, long nFeatureId );

 Fetch a feature by it's identifier.

 This function will attempt to read the identified feature.  The nFID
 value cannot be OGRNullFID.  Success or failure of this operation is
 unaffected by the spatial or attribute filters.

 If this function returns a non-NULL feature, it is guaranteed that it's 
 feature id (OGR_F_GetFID()) will be the same as nFID.

 Use OGR_L_TestCapability(OLCRandomRead) to establish if this layer
 supports efficient random access reading via OGR_L_GetFeature(); however, 
 the call should always work if the feature exists as a fallback 
 implementation just scans all the features in the layer looking for the 
 desired feature.
 
 Sequential reads are generally considered interrupted by a 
 OGR_L_GetFeature() call.

 This function is the same as the C++ method OGRLayer::GetFeature( ).

 @param hLayer handle to the layer that owned the feature.
 @param nFeatureId the feature id of the feature to read. 

 @return an handle to a feature now owned by the caller, or NULL on failure. 

*/

/**
 
 \fn OGRErr OGRLayer::SetFeature( OGRFeature * poFeature );

 Rewrite an existing feature.

 This method will write a feature to the layer, based on the feature id
 within the OGRFeature.   

 Use OGRLayer::TestCapability(OLCRandomWrite) to establish if this layer
 supports random access writing via SetFeature().

 This method is the same as the C function OGR_L_SetFeature().

 @param poFeature the feature to write.

 @return OGRERR_NONE if the operation works, otherwise an appropriate error
 code.

*/

/**
 
 \fn OGRErr OGR_L_SetFeature( OGRLayerH hLayer, OGRFeatureH hFeat );

 Rewrite an existing feature.

 This function will write a feature to the layer, based on the feature id
 within the OGRFeature.   

 Use OGR_L_TestCapability(OLCRandomWrite) to establish if this layer
 supports random access writing via OGR_L_SetFeature().

 This function is the same as the C++ method OGRLayer::SetFeature().

 @param hLayer handle to the layer to write the feature.
 @param hFeat the feature to write.

 @return OGRERR_NONE if the operation works, otherwise an appropriate error
 code.

*/

/**

 \fn OGRErr OGRLayer::CreateFeature( OGRFeature * poFeature );

 Create and write a new feature within a layer.

 The passed feature is written to the layer as a new feature, rather than
 overwriting an existing one.  If the feature has a feature id other than
 OGRNullFID, then the native implementation may use that as the feature id
 of the new feature, but not necessarily.  Upon successful return the 
 passed feature will have been updated with the new feature id. 

 This method is the same as the C function OGR_L_CreateFeature().

 @param poFeature the feature to write to disk. 

 @return OGRERR_NONE on success.

*/

/**

 \fn OGRErr OGR_L_CreateFeature( OGRLayerH hLayer, OGRFeatureH hFeat );

 Create and write a new feature within a layer.

 The passed feature is written to the layer as a new feature, rather than
 overwriting an existing one.  If the feature has a feature id other than
 OGRNullFID, then the native implementation may use that as the feature id
 of the new feature, but not necessarily.  Upon successful return the 
 passed feature will have been updated with the new feature id. 

 This function is the same as the C++ method OGRLayer::CreateFeature().

 @param hLayer handle to the layer to write the feature to.
 @param hFeat the handle of the feature to write to disk. 

 @return OGRERR_NONE on success.

*/

/**

 \fn OGRErr OGRLayer::DeleteFeature( long nFID );

 Delete feature from layer.

 The feature with the indicated feature id is deleted from the layer if
 supported by the driver.  Most drivers do not support feature deletion,
 and will return OGRERR_UNSUPPORTED_OPERATION.  The TestCapability()
 layer method may be called with OLCDeleteFeature to check if the driver 
 supports feature deletion.

 This method is the same as the C function OGR_L_DeleteFeature().

 @param poFeature the feature to write to disk. 

 @return OGRERR_NONE on success.

*/

/**

 \fn OGRErr OGR_L_DeleteFeature( OGRLayerH hLayer, long nFID );

 Delete feature from layer.

 The feature with the indicated feature id is deleted from the layer if
 supported by the driver.  Most drivers do not support feature deletion,
 and will return OGRERR_UNSUPPORTED_OPERATION.  The OGR_L_TestCapability()
 function may be called with OLCDeleteFeature to check if the driver 
 supports feature deletion.

 This method is the same as the C++ method OGRLayer::DeleteFeature().

 @param poFeature the feature to write to disk. 

 @return OGRERR_NONE on success.


*/


/**

 \fn int OGRLayer::TestCapability( const char * pszCap );

 Test if this layer supported the named capability.

 The capability codes that can be tested are represented as strings, but
 #defined constants exists to ensure correct spelling.  Specific layer 
 types may implement class specific capabilities, but this can't generally
 be discovered by the caller. <p>

 <ul>

 <li> <b>OLCRandomRead</b> / "RandomRead": TRUE if the GetFeature() method 
works for this layer.<p>

 <li> <b>OLCSequentialWrite</b> / "SequentialWrite": TRUE if the 
CreateFeature() method works for this layer.  Note this means that this 
particular layer is writable.  The same OGRLayer class  may returned FALSE 
for other layer instances that are effectively read-only.<p>

 <li> <b>OLCRandomWrite</b> / "RandomWrite": TRUE if the SetFeature() method
is operational on this layer.   Note this means that this 
particular layer is writable.  The same OGRLayer class  may returned FALSE 
for other layer instances that are effectively read-only.<p>

 <li> <b>OLCFastSpatialFilter</b> / "FastSpatialFilter": TRUE if this layer
implements spatial filtering efficiently.  Layers that effectively read all
features, and test them with the OGRFeature intersection methods should
return FALSE.  This can be used as a clue by the application whether it 
should build and maintain it's own spatial index for features in this layer.<p>

 <li> <b>OLCFastFeatureCount</b> / "FastFeatureCount": 
TRUE if this layer can return a feature
count (via OGRLayer::GetFeatureCount()) efficiently ... ie. without counting
the features.  In some cases this will return TRUE until a spatial filter is
installed after which it will return FALSE.<p>

 <li> <b>OLCFastGetExtent</b> / "FastGetExtent": 
TRUE if this layer can return its data extent (via OGRLayer::GetExtent()) efficiently ... ie. without scanning all the features.  In some cases this will return TRUE until a spatial filter is installed after which it will return FALSE.<p>

</ul>
 
 This method is the same as the C function OGR_L_TestCapability().

 @param pszCap the name of the capability to test.

 @return TRUE if the layer has the requested capability, or FALSE otherwise.
OGRLayers will return FALSE for any unrecognised capabilities.<p>

*/


/**

 \fn int OGR_L_TestCapability( OGRLayerH hLayer, const char *pszCap );

 Test if this layer supported the named capability.

 The capability codes that can be tested are represented as strings, but
 #defined constants exists to ensure correct spelling.  Specific layer 
 types may implement class specific capabilities, but this can't generally
 be discovered by the caller. <p>

 <ul>

 <li> <b>OLCRandomRead</b> / "RandomRead": TRUE if the OGR_L_GetFeature() 
function works for this layer.<p>

 <li> <b>OLCSequentialWrite</b> / "SequentialWrite": TRUE if the 
OGR_L_CreateFeature() function works for this layer.  Note this means that 
this particular layer is writable.  The same OGRLayer class  may returned 
FALSE for other layer instances that are effectively read-only.<p>

 <li> <b>OLCRandomWrite</b> / "RandomWrite": TRUE if the OGR_L_SetFeature()
function is operational on this layer.   Note this means that this 
particular layer is writable.  The same OGRLayer class  may returned FALSE 
for other layer instances that are effectively read-only.<p>

 <li> <b>OLCFastSpatialFilter</b> / "FastSpatialFilter": TRUE if this layer
implements spatial filtering efficiently.  Layers that effectively read all
features, and test them with the OGRFeature intersection methods should
return FALSE.  This can be used as a clue by the application whether it 
should build and maintain it's own spatial index for features in this 
layer.<p>

 <li> <b>OLCFastFeatureCount</b> / "FastFeatureCount": 
TRUE if this layer can return a feature
count (via OGR_L_GetFeatureCount()) efficiently ... ie. without counting
the features.  In some cases this will return TRUE until a spatial filter is
installed after which it will return FALSE.<p>

 <li> <b>OLCFastGetExtent</b> / "FastGetExtent": 
TRUE if this layer can return its data extent (via OGR_L_GetExtent()) 
efficiently ... ie. without scanning all the features.  In some cases this 
will return TRUE until a spatial filter is installed after which it will 
return FALSE.<p>

</ul>
 
 This function is the same as the C++ method OGRLayer::TestCapability().

 @param hLayer handle to the layer to get the capability from.
 @param pszCap the name of the capability to test.

 @return TRUE if the layer has the requested capability, or FALSE otherwise.
OGRLayers will return FALSE for any unrecognised capabilities.<p>

*/

/**
 \fn const char *OGRLayer::GetInfo( const char *pszTag );

 Fetch metadata from layer.

 This method can be used to fetch various kinds of metadata or layer 
 specific information encoded as a string.  It is anticipated that various
 tag values will be defined with well known semantics, while other tags will
 be used for driver/application specific purposes.  

 This method is deprecated and will be replaced with a more general 
 metadata model in the future. At this time no drivers return information
 via the GetInfo() call. 

 @param pszTag the tag for which information is being requested.

 @return the value of the requested tag, or NULL if that tag does not
 have a value, or is unknown.

*/

/**
 \fn OGRErr OGRLayer::SyncToDisk();

Flush pending changes to disk.

This call is intended to force the layer to flush any pending writes to
disk, and leave the disk file in a consistent state.  It would not normally
have any effect on read-only datasources. 

Some layers do not implement this method, and will still return 
OGRERR_NONE.  The default implementation just returns OGRERR_NONE.  An error
is only returned if an error occurs while attempting to flush to disk.  

This method is the same as the C function OGR_L_SyncToDisk().

@return OGRERR_NONE if no error occurs (even if nothing is done) or an
error code.
*/

/**
 \fn int OGRLayer::Reference();

Increment layer reference count.

This method is the same as the C function OGR_L_Reference().

@return the reference count after incrementing.
*/
				         
/**
 \fn int OGRLayer::Dereference();

Decrement layer reference count.

This method is the same as the C function OGR_L_Dereference().

@return the reference count after decrementing.
*/
				         
/**
 \fn int OGRLayer::GetRefCount() const;

Fetch reference count.

This method is the same as the C function OGR_L_GetRefCount().

@return the current reference count for the layer object itself.
*/

/**
\fn OGRErr OGRLayer::CreateField( OGRFieldDefn *poField, 
				  int bApproxOK = TRUE );

Create a new field on a layer.  You must use this to create new fields
on a real layer. Internally the OGRFeatureDefn for the layer will be updated
to reflect the new field.  Applications should never modify the OGRFeatureDefn
used by a layer directly.

This function is the same as the C function OGR_L_CreateField().

@param poField field definition to write to disk. 
@param bApproxOK If TRUE, the field may be created in a slightly different
form depending on the limitations of the format driver.

@return OGRERR_NONE on success.
*/
 
/**

 \fn OGRErr OGR_L_CreateField( OGRLayerH hLayer, OGRFieldDefnH hField, 
                          int bApproxOK );

Create a new field on a layer.  You must use this to create new fields
on a real layer. Internally the OGRFeatureDefn for the layer will be updated
to reflect the new field.  Applications should never modify the OGRFeatureDefn
used by a layer directly.

 This function is the same as the C++ method OGRLayer::CreateField().

 @param hLayer handle to the layer to write the field definition.
 @param hField handle of the field definition to write to disk. 
 @param bApproxOK If TRUE, the field may be created in a slightly different
form depending on the limitations of the format driver.

 @return OGRERR_NONE on success.

*/

/**

 \fn OGRErr OGR_L_StartTransaction( OGRLayerH hLayer );

 What does this do?.

 This function is the same as the C++ method OGRLayer::StartTransaction().

 @param hLayer handle to the layer ?

 @return OGRERR_NONE on success.

*/

/**

 \fn OGRErr OGR_L_CommitTransaction( OGRLayerH hLayer );

 What does this do?.

 This function is the same as the C++ method OGRLayer::CommitTransaction().

 @param hLayer handle to the layer?

 @return OGRERR_NONE on success.

*/

/**

 \fn OGRErr OGR_L_RollbackTransaction( OGRLayerH hLayer );

 What does this do?.

 This function is the same as the C++ method OGRLayer::RollbackTransaction().

 @param hLayer handle to the layer?

 @return OGRERR_NONE on success.

*/

