# GDALPamDataset Class Reference

A subclass of GDALDataset which introduces the ability to save and restore auxilary information (coordinate system, gcps, metadata, etc) not supported by a file format via an "auxilary metadata" file with the .aux.xml extension. More...

`#include <gdal_pam.h>`

Inheritance diagram for GDALPamDataset:

List of all members.

## Public Member Functions
virtual void | FlushCache (void)
| Flush all write cached data to disk.
virtual const char * | GetProjectionRef (void)
| Fetch the projection definition string for this dataset.
virtual CPLErr | SetProjection (const char *)
| Set the projection reference string for this dataset.
virtual CPLErr | GetGeoTransform (double *)
| Fetch the affine transformation coefficients.
virtual CPLErr | SetGeoTransform (double *)
| Set the affine transformation coefficients.
virtual int | GetGCPCount ()
| Get number of GCPs.
virtual const char * | GetGCPProjection ()
| Get output projection for GCPs.
virtual const GDAL_GCP * | GetGCPs ()
| Fetch GCPs.
virtual CPLErr | SetGCPs (int nGCPCount, const GDAL_GCP *pasGCPList, const char *pszGCPProjection)
| Assign GCPs.
virtual CPLErr | SetMetadata (char **papszMetadata, const char *pszDomain="")
| Set metadata.
virtual CPLErr | SetMetadataItem (const char *pszName, const char *pszValue, const char *pszDomain="")
| Set single metadata item.
virtual char ** | GetMetadata (const char *pszDomain="")
| Fetch metadata.
virtual const char * | GetMetadataItem (const char *pszName, const char *pszDomain="")
| Fetch single metadata item.
virtual char ** | GetFileList (void)
| Fetch files forming dataset.
virtual CPLErr | CloneInfo (GDALDataset *poSrcDS, int nCloneInfoFlags)
virtual CPLErr | IBuildOverviews (const char *pszResampling, int nOverviews, int *panOverviewList, int nListBands, int *panBandList, GDALProgressFunc pfnProgress, void *pProgressData)
void | MarkPamDirty ()
GDALDatasetPamInfo * | GetPamInfo ()
int | GetPamFlags ()
void | SetPamFlags (int nValue)
## Protected Member Functions
virtual CPLXMLNode * | SerializeToXML (const char *)
virtual CPLErr | XMLInit (CPLXMLNode *, const char *)
virtual CPLErr | TryLoadXML (char **papszSiblingFiles=NULL)
virtual CPLErr | TrySaveXML ()
CPLErr | TryLoadAux (char **papszSiblingFiles=NULL)
CPLErr | TrySaveAux ()
virtual const char * | BuildPamFilename ()
void | PamInitialize ()
void | PamClear ()
void | SetPhysicalFilename (const char *)
const char * | GetPhysicalFilename ()
void | SetSubdatasetName (const char *)
const char * | GetSubdatasetName ()
## Protected Attributes
int | nPamFlags
GDALDatasetPamInfo * | psPam
## Friends
class | GDALPamRasterBand

## Detailed Description

A subclass of GDALDataset which introduces the ability to save and restore auxilary information (coordinate system, gcps, metadata, etc) not supported by a file format via an "auxilary metadata" file with the .aux.xml extension.

### Enabling PAM

PAM support can be enabled (resp. disabled) in GDAL by setting the GDAL_PAM_ENABLED configuration option (via CPLSetConfigOption(), or the environment) to the value of YES (resp. NO). Note: The default value is build dependant and defaults to YES in Windows and Unix builds.

### PAM Proxy Files

In order to be able to record auxilary information about files on read-only media such as CDROMs or in directories where the user does not have write permissions, it is possible to enable the "PAM Proxy Database". When enabled the .aux.xml files are kept in a different directory, writable by the user. Overviews will also be stored in the PAM proxy directory.

To enable this, set the GDAL_PAM_PROXY_DIR configuration option to be the name of the directory where the proxies should be kept. The configuration option must be set *before* the first access to PAM, because its value is cached for later access.

### Adding PAM to Drivers

Drivers for physical file formats that wish to support persistent auxilary metadata in addition to that for the format itself should derive their dataset class from GDALPamDataset instead of directly from GDALDataset. The raster band classes should also be derived from GDALPamRasterBand.

They should also call something like this near the end of the Open() method:

          poDS->SetDescription( poOpenInfo->pszFilename );
          poDS->TryLoadXML();

The SetDescription() is necessary so that the dataset will have a valid filename set as the description before TryLoadXML() is called. TryLoadXML() will look for an .aux.xml file with the same basename as the dataset and in the same directory. If found the contents will be loaded and kept track of in the GDALPamDataset and GDALPamRasterBand objects. When a call like GetProjectionRef() is not implemented by the format specific class, it will fall through to the PAM implementation which will return information if it was in the .aux.xml file.

Drivers should also try to call the GDALPamDataset/GDALPamRasterBand methods as a fallback if their implementation does not find information. This allows using the .aux.xml for variations that can't be stored in the format. For instance, the GeoTIFF driver GetProjectionRef() looks like this:

          if( EQUAL(pszProjection,"") )
              return GDALPamDataset::GetProjectionRef();
          else
              return( pszProjection );

So if the geotiff header is missing, the .aux.xml file will be consulted.

Similarly, if SetProjection() were called with a coordinate system not supported by GeoTIFF, the SetProjection() method should pass it on to the GDALPamDataset::SetProjection() method after issuing a warning that the information can't be represented within the file itself.

Drivers for subdataset based formats will also need to declare the name of the physical file they are related to, and the name of their subdataset before calling TryLoadXML().

          poDS->SetDescription( poOpenInfo->pszFilename );
          poDS->SetPhysicalFilename( poDS->pszFilename );
          poDS->SetSubdatasetName( osSubdatasetName );

          poDS->TryLoadXML();

## Member Function Documentation

void GDALPamDataset::FlushCache | ( | void |  | ) | `[virtual]`

Flush all write cached data to disk.

Any raster (or other GDAL) data written via GDAL calls, but buffered internally will be written to disk.

Using this method does not prevent use from calling GDALClose() to properly close a dataset and ensure that important data not addressed by FlushCache() is written in the file.

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

Reimplemented from GDALDataset.

References GDALDataset::FlushCache().

const char * GDALPamDataset::GetProjectionRef | ( | void |  | ) | `[virtual]`

Fetch the projection definition string for this dataset.

Same as the C function GDALGetProjectionRef().

The returned string defines the projection coordinate system of the image in OpenGIS WKT format. It should be suitable for use with the OGRSpatialReference class.

When a projection definition is not available an empty (but not NULL) string is returned.

Returns:
  a pointer to an internal projection reference string. It should not be altered, freed or expected to last for long.

See also:
  http://www.gdal.org/ogr/osr_tutorial.html

Reimplemented from GDALDataset.

References GDALDataset::GetProjectionRef().

CPLErr GDALPamDataset::SetProjection | ( | const char * | pszProjection | ) | `[virtual]`

Set the projection reference string for this dataset.

The string should be in OGC WKT or PROJ.4 format. An error may occur because of incorrectly specified projection strings, because the dataset is not writable, or because the dataset does not support the indicated projection. Many formats do not support writing projections.

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

Parameters:

  | pszProjection | projection reference string.

Returns:
  CE_Failure if an error occurs, otherwise CE_None.

Reimplemented from GDALDataset.

References GDALDataset::SetProjection().

CPLErr GDALPamDataset::GetGeoTransform | ( | double * | padfTransform | ) | `[virtual]`

Fetch the affine transformation coefficients.

Fetches the coefficients for transforming between pixel/line (P,L) raster space, and projection coordinates (Xp,Yp) space.

       Xp = padfTransform[0] + P*padfTransform[1] + L*padfTransform[2];
       Yp = padfTransform[3] + P*padfTransform[4] + L*padfTransform[5];

In a north up image, padfTransform[1] is the pixel width, and padfTransform[5] is the pixel height. The upper left corner of the upper left pixel is at position (padfTransform[0],padfTransform[3]).

The default transform is (0,1,0,0,0,1) and should be returned even when a CE_Failure error is returned, such as for formats that don't support transformation to projection coordinates.

NOTE: GetGeoTransform() isn't expressive enough to handle the variety of OGC Grid Coverages pixel/line to projection transformation schemes. Eventually this method will be depreciated in favour of a more general scheme.

This method does the same thing as the C GDALGetGeoTransform() function.

Parameters:

  | padfTransform | an existing six double buffer into which the transformation will be placed.

Returns:
  CE_None on success, or CE_Failure if no transform can be fetched.

Reimplemented from GDALDataset.

References GDALDataset::GetGeoTransform().

CPLErr GDALPamDataset::SetGeoTransform | ( | double * | padfTransform | ) | `[virtual]`

Set the affine transformation coefficients.

See GetGeoTransform() for details on the meaning of the padfTransform coefficients.

This method does the same thing as the C GDALSetGeoTransform() function.

Parameters:

  | padfTransform | a six double buffer containing the transformation coefficients to be written with the dataset.

Returns:
  CE_None on success, or CE_Failure if this transform cannot be written.

Reimplemented from GDALDataset.

References GDALDataset::SetGeoTransform().

int GDALPamDataset::GetGCPCount | ( |  | ) | `[virtual]`

Get number of GCPs.

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

Returns:
  number of GCPs for this dataset. Zero if there are none.

Reimplemented from GDALDataset.

References GDALDataset::GetGCPCount().

const char * GDALPamDataset::GetGCPProjection | ( |  | ) | `[virtual]`

Get output projection for GCPs.

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

The projection string follows the normal rules from GetProjectionRef().

Returns:
  internal projection string or "" if there are no GCPs. It should not be altered, freed or expected to last for long.

Reimplemented from GDALDataset.

References GDALDataset::GetGCPProjection().

const GDAL_GCP * GDALPamDataset::GetGCPs | ( |  | ) | `[virtual]`

Fetch GCPs.

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

Returns:
  pointer to internal GCP structure list. It should not be modified, and may change on the next GDAL call.

Reimplemented from GDALDataset.

References GDALDataset::GetGCPs().

CPLErr GDALPamDataset::SetGCPs | ( | int | nGCPCount,
|  | const GDAL_GCP * | pasGCPList,
|  | const char * | pszGCPProjection |
| ) |  |  | `[virtual]`

Assign GCPs.

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

This method assigns the passed set of GCPs to this dataset, as well as setting their coordinate system. Internally copies are made of the coordinate system and list of points, so the caller remains resposible for deallocating these arguments if appropriate.

Most formats do not support setting of GCPs, even foramts that can handle GCPs. These formats will return CE_Failure.

Parameters:

  | nGCPCount | number of GCPs being assigned.
  | pasGCPList | array of GCP structures being assign (nGCPCount in array).
  | pszGCPProjection | the new OGC WKT coordinate system to assign for the GCP output coordinates. This parameter should be "" if no output coordinate system is known.

Returns:
  CE_None on success, CE_Failure on failure (including if action is not supported for this format).

Reimplemented from GDALDataset.

References GDALDataset::SetGCPs().

CPLErr GDALPamDataset::SetMetadata | ( | char ** | papszMetadataIn,
|  | const char * | pszDomain = `""` |
| ) |  |  | `[virtual]`

Set metadata.

The C function GDALSetMetadata() does the same thing as this method.

Parameters:

  | papszMetadataIn | the metadata in name=value string list format to apply.
  | pszDomain | the domain of interest. Use "" or NULL for the default domain.

Returns:
  CE_None on success, CE_Failure on failure and CE_Warning if the metadata has been accepted, but is likely not maintained persistently by the underlying object between sessions.

Reimplemented from GDALMajorObject.

References GDALMajorObject::SetMetadata().

CPLErr GDALPamDataset::SetMetadataItem | ( | const char * | pszName,
|  | const char * | pszValue,
|  | const char * | pszDomain = `""` |
| ) |  |  | `[virtual]`

Set single metadata item.

The C function GDALSetMetadataItem() does the same thing as this method.

Parameters:

  | pszName | the key for the metadata item to fetch.
  | pszValue | the value to assign to the key.
  | pszDomain | the domain to set within, use NULL for the default domain.

Returns:
  CE_None on success, or an error code on failure.

Reimplemented from GDALMajorObject.

References GDALMajorObject::SetMetadataItem().

Referenced by GetMetadataItem().

char ** GDALPamDataset::GetMetadata | ( | const char * | pszDomain = `""` | ) | `[virtual]`

Fetch metadata.

The returned string list is owned by the object, and may change at any time. It is formated as a "Name=value" list with the last pointer value being NULL. Use the the CPL StringList functions such as CSLFetchNameValue() to manipulate it.

Note that relatively few formats return any metadata at this time.

This method does the same thing as the C function GDALGetMetadata().

Parameters:

  | pszDomain | the domain of interest. Use "" or NULL for the default domain.

Returns:
  NULL or a string list.

Reimplemented from GDALMajorObject.

References GDALMajorObject::GetMetadata().

const char * GDALPamDataset::GetMetadataItem | ( | const char * | pszName,
|  | const char * | pszDomain = `""` |
| ) |  |  | `[virtual]`

Fetch single metadata item.

The C function GDALGetMetadataItem() does the same thing as this method.

Parameters:

  | pszName | the key for the metadata item to fetch.
  | pszDomain | the domain to fetch for, use NULL for the default domain.

Returns:
  NULL on failure to find the key, or a pointer to an internal copy of the value string on success.

Reimplemented from GDALMajorObject.

References CPLFormFilename(), CPLGetPath(), GDALMajorObject::GetDescription(), GDALMajorObject::GetMetadataItem(), and SetMetadataItem().

char ** GDALPamDataset::GetFileList | ( | void |  | ) | `[virtual]`

Fetch files forming dataset.

Returns a list of files believed to be part of this dataset. If it returns an empty list of files it means there is believed to be no local file system files associated with the dataset (for instance a virtual dataset). The returned file list is owned by the caller and should be deallocated with CSLDestroy().

The returned filenames will normally be relative or absolute paths depending on the path used to originally open the dataset. The strings will be UTF-8 encoded.

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

Returns:
  NULL or a NULL terminated array of file names.

Reimplemented from GDALDataset.

References CPLGetFilename(), GDALDataset::GetFileList(), and VSIStatExL().

The documentation for this class was generated from the following files:

- gdal_pam.h
- gdalpamdataset.cpp

Generated for GDAL by 1.5.6.