Package osgeo :: Module ogr :: Class Layer |
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# Class Layer

source code

Proxy of C++ OGRLayerShadow class

Instance Methods | [hide private]
__init__(self, *args, **kwargs) | source code
__repr__(self) | source code
int |
GetRefCount(self) int OGR_L_GetRefCount(OGRLayerH hLayer) | source code
SetSpatialFilter(self, *args) SetSpatialFilter(self, Geometry filter) | source code
SetSpatialFilterRect(self, *args) SetSpatialFilterRect(self, double minx, double miny, double maxx, double maxy) | source code
Geometry |
GetSpatialFilter(self) OGRGeometryH OGR_L_GetSpatialFilter(OGRLayerH hLayer) | source code
SetAttributeFilter(self, *args) SetAttributeFilter(self, char filter_string) -> OGRErr | source code
ResetReading(self) void OGR_L_ResetReading(OGRLayerH hLayer) | source code
char |
GetName(self) const char* OGR_L_GetName(OGRLayerH hLayer) | source code
OGRwkbGeometryType |
GetGeomType(self) OGRwkbGeometryType OGR_L_GetGeomType(OGRLayerH hLayer) | source code
char |
GetGeometryColumn(self) const char* OGR_L_GetGeometryColumn(OGRLayerH hLayer) | source code
char |
GetFIDColumn(self) const char* OGR_L_GetFIDColumn(OGRLayerH hLayer) | source code
GetFeature(self, *args) GetFeature(self, long fid) -> Feature | source code
Feature |
GetNextFeature(self) OGRFeatureH OGR_L_GetNextFeature(OGRLayerH hLayer) | source code
SetNextByIndex(self, *args) SetNextByIndex(self, long new_index) -> OGRErr | source code
SetFeature(self, *args) SetFeature(self, Feature feature) -> OGRErr | source code
CreateFeature(self, *args) CreateFeature(self, Feature feature) -> OGRErr | source code
DeleteFeature(self, *args) DeleteFeature(self, long fid) -> OGRErr | source code
OGRErr |
SyncToDisk(self) OGRErr OGR_L_SyncToDisk(OGRLayerH hDS) | source code
FeatureDefn |
GetLayerDefn(self) OGRFeatureDefnH OGR_L_GetLayerDefn(OGRLayerH hLayer) | source code
GetFeatureCount(self, *args, **kwargs) GetFeatureCount(self, int force = 1) -> int | source code
GetExtent(self, *args, **kwargs) GetExtent(self, int force = 1, int can_return_null = 0) | source code
TestCapability(self, *args) TestCapability(self, char cap) -> bool | source code
CreateField(self, *args, **kwargs) CreateField(self, FieldDefn field_def, int approx_ok = 1) -> OGRErr | source code
DeleteField(self, *args) DeleteField(self, int iField) -> OGRErr | source code
ReorderField(self, *args) ReorderField(self, int iOldFieldPos, int iNewFieldPos) -> OGRErr | source code
ReorderFields(self, *args) ReorderFields(self, int nList) -> OGRErr | source code
AlterFieldDefn(self, *args) AlterFieldDefn(self, int iField, FieldDefn field_def, int nFlags) -> OGRErr | source code
OGRErr |
StartTransaction(self) OGRErr OGR_L_StartTransaction(OGRLayerH hLayer) | source code
OGRErr |
CommitTransaction(self) OGRErr OGR_L_CommitTransaction(OGRLayerH hLayer) | source code
OGRErr |
RollbackTransaction(self) OGRErr OGR_L_RollbackTransaction(OGRLayerH hLayer) | source code
SpatialReference |
GetSpatialRef(self) OGRSpatialReferenceH OGR_L_GetSpatialRef(OGRLayerH hLayer) | source code
GIntBig |
GetFeaturesRead(self) GIntBig OGR_L_GetFeaturesRead(OGRLayerH hLayer) | source code
SetIgnoredFields(self, *args) SetIgnoredFields(self, char options) -> OGRErr | source code
Reference(self) For backwards compatibility only. | source code
Dereference(self) For backwards compatibility only. | source code
__len__(self) Returns the number of features in the layer | source code
__getitem__(self, value) Support list and slice -like access to the layer. | source code
CreateFields(fields) Create a list of fields on the Layer | source code
__iter__(self) | source code
next(self) | source code
schema(self) | source code

Class Variables | [hide private]
| __swig_setmethods__ = `{}`
| __setattr__ = `lambda self, name, value:`
| __swig_getmethods__ = `{}`
| __getattr__ = `lambda self, name:`

Method Details | [hide private]

### SetSpatialFilter(self, *args) | source code
    SetSpatialFilter(self, Geometry filter)

    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.

    Parameters:
    -----------

    hLayer:  handle to the layer on which to set the spatial filter.

    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.

### SetSpatialFilterRect(self, *args) | source code
    SetSpatialFilterRect(self, double minx, double miny, double maxx, double maxy)

    void
    OGR_L_SetSpatialFilterRect(OGRLayerH hLayer, double dfMinX, double
    dfMinY, double dfMaxX, double dfMaxY)

    Set a new rectangular spatial filter.

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

    The x/y values should be in the same coordinate system as the layer as
    a whole (as returned by OGRLayer::GetSpatialRef()). Internally this
    method is normally implemented as creating a 5 vertex closed
    rectangular polygon and passing it to OGRLayer::SetSpatialFilter(). It
    exists as a convenience.

    The only way to clear a spatial filter set with this method is to call
    OGRLayer::SetSpatialFilter(NULL).

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

    Parameters:
    -----------

    hLayer:  handle to the layer on which to set the spatial filter.

    dfMinX:  the minimum X coordinate for the rectangular region.

    dfMinY:  the minimum Y coordinate for the rectangular region.

    dfMaxX:  the maximum X coordinate for the rectangular region.

    dfMaxY:  the maximum Y coordinate for the rectangular region.

### GetSpatialFilter(self) | source code
    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().

    Parameters:
    -----------

    hLayer:  handle to the layer to get the spatial filter from.

    an handle to the spatial filter geometry.
Returns: Geometry

### SetAttributeFilter(self, *args) | source code
    SetAttributeFilter(self, char filter_string) -> OGRErr

    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().

    Parameters:
    -----------

    hLayer:  handle to the layer on which attribute query will be
    executed.

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

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

### ResetReading(self) | source code
    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().

    Parameters:
    -----------

    hLayer:  handle to the layer on which features are read.

### GetName(self) | source code
    const char* OGR_L_GetName(OGRLayerH
    hLayer)

    Return the layer name.

    This returns the same content as
    OGR_FD_GetName(OGR_L_GetLayerDefn(hLayer)), but for a few drivers,
    calling OGR_L_GetName() directly can avoid lengthy layer definition
    initialization.

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

    Parameters:
    -----------

    hLayer:  handle to the layer.

    the layer name (must not been freed)

    OGR 1.8.0
Returns: char

### GetGeomType(self) | source code
    OGRwkbGeometryType
    OGR_L_GetGeomType(OGRLayerH hLayer)

    Return the layer geometry type.

    This returns the same result as
    OGR_FD_GetGeomType(OGR_L_GetLayerDefn(hLayer)), but for a few drivers,
    calling OGR_L_GetGeomType() directly can avoid lengthy layer
    definition initialization.

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

    Parameters:
    -----------

    hLayer:  handle to the layer.

    the geometry type

    OGR 1.8.0
Returns: OGRwkbGeometryType

### GetGeometryColumn(self) | source code
    const char*
    OGR_L_GetGeometryColumn(OGRLayerH hLayer)

    This method returns the name of the underlying database column being
    used as the geometry column, or "" if not supported.

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

    Parameters:
    -----------

    hLayer:  handle to the layer

    geometry column name.
Returns: char

### GetFIDColumn(self) | source code
    const char*
    OGR_L_GetFIDColumn(OGRLayerH hLayer)

    This method returns the name of the underlying database column being
    used as the FID column, or "" if not supported.

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

    Parameters:
    -----------

    hLayer:  handle to the layer

    fid column name.
Returns: char

### GetFeature(self, *args) | source code
    GetFeature(self, long fid) -> Feature

    OGRFeatureH
    OGR_L_GetFeature(OGRLayerH hLayer, long nFeatureId)

    Fetch a feature by its 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 its
    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.

    The returned feature should be free with OGR_F_Destroy().

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

    Parameters:
    -----------

    hLayer:  handle to the layer that owned the feature.

    nFeatureId:  the feature id of the feature to read.

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

### GetNextFeature(self) | source code
    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
    with OGR_F_Destroy(). 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.

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

    Parameters:
    -----------

    hLayer:  handle to the layer from which feature are read.

    an handle to a feature, or NULL if no more features are available.
Returns: Feature

### SetNextByIndex(self, *args) | source code
    SetNextByIndex(self, long new_index) -> OGRErr

    OGRErr
    OGR_L_SetNextByIndex(OGRLayerH hLayer, long nIndex)

    Move read cursor to the nIndex'th feature in the current resultset.

    This method allows positioning of a layer such that the
    GetNextFeature() call will read the requested feature, where nIndex is
    an absolute index into the current result set. So, setting it to 3
    would mean the next feature read with GetNextFeature() would have been
    the 4th feature to have been read if sequential reading took place
    from the beginning of the layer, including accounting for spatial and
    attribute filters.

    Only in rare circumstances is SetNextByIndex() efficiently
    implemented. In all other cases the default implementation which calls
    ResetReading() and then calls GetNextFeature() nIndex times is used.
    To determine if fast seeking is available on the current layer use the
    TestCapability() method with a value of OLCFastSetNextByIndex.

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

    Parameters:
    -----------

    hLayer:  handle to the layer

    nIndex:  the index indicating how many steps into the result set to
    seek.

    OGRERR_NONE on success or an error code.

### SetFeature(self, *args) | source code
    SetFeature(self, Feature feature) -> OGRErr

    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().

    Parameters:
    -----------

    hLayer:  handle to the layer to write the feature.

    hFeat:  the feature to write.

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

### CreateFeature(self, *args) | source code
    CreateFeature(self, Feature feature) -> OGRErr

    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().

    Parameters:
    -----------

    hLayer:  handle to the layer to write the feature to.

    hFeat:  the handle of the feature to write to disk.

    OGRERR_NONE on success.

### DeleteFeature(self, *args) | source code
    DeleteFeature(self, long fid) -> OGRErr

    OGRErr
    OGR_L_DeleteFeature(OGRLayerH hDS, 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().

    Parameters:
    -----------

    hLayer:  handle to the layer

    nFID:  the feature id to be deleted from the layer

    OGRERR_NONE on success.

### SyncToDisk(self) | source code
    OGRErr OGR_L_SyncToDisk(OGRLayerH
    hDS)

    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.

    In any event, you should always close any opened datasource with
    OGR_DS_Destroy() that will ensure all data is correctly flushed.

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

    Parameters:
    -----------

    hLayer:  handle to the layer

    OGRERR_NONE if no error occurs (even if nothing is done) or an error
    code.
Returns: OGRErr

### GetLayerDefn(self) | source code
    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().

    Parameters:
    -----------

    hLayer:  handle to the layer to get the schema information.

    an handle to the feature definition.
Returns: FeatureDefn

### GetFeatureCount(self, *args, **kwargs) | source code
    GetFeatureCount(self, int force = 1) -> int

    int
    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.

    Note that some implementations of this method may alter the read
    cursor of the layer.

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

    Parameters:
    -----------

    hLayer:  handle to the layer that owned the features.

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

    feature count, -1 if count not known.

### GetExtent(self, *args, **kwargs) | source code
    GetExtent(self, int force = 1, int can_return_null = 0)

    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.

    Depending on the drivers, the returned extent may or may not take the
    spatial filter into account. 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.

    Note that some implementations of this method may alter the read
    cursor of the layer.

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

    Parameters:
    -----------

    hLayer:  handle to the layer from which to get extent.

    psExtent:  the structure in which the extent value will be returned.

    bForce:  Flag indicating whether the extent should be computed even if
    it is expensive.

    OGRERR_NONE on success, OGRERR_FAILURE if extent not known.

### TestCapability(self, *args) | source code
    TestCapability(self, char cap) -> bool

    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.

    OLCRandomRead / "RandomRead": TRUE if the GetFeature() method is
    implemented in an optimized way for this layer, as opposed to the
    default implementation using ResetReading() and GetNextFeature() to
    find the requested feature id.

    OLCSequentialWrite / "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.

    OLCRandomWrite / "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.

    OLCFastSpatialFilter / "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 its own spatial index for
    features in this layer.

    OLCFastFeatureCount / "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.

    OLCFastGetExtent / "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.

    OLCFastSetNextByIndex / "FastSetNextByIndex": TRUE if this layer can
    perform the SetNextByIndex() call efficiently, otherwise FALSE.

    OLCCreateField / "CreateField": TRUE if this layer can create new
    fields on the current layer using CreateField(), otherwise FALSE.

    OLCDeleteField / "DeleteField": TRUE if this layer can delete
    existing fields on the current layer using DeleteField(), otherwise
    FALSE.

    OLCReorderFields / "ReorderFields": TRUE if this layer can reorder
    existing fields on the current layer using ReorderField() or
    ReorderFields(), otherwise FALSE.

    OLCAlterFieldDefn / "AlterFieldDefn": TRUE if this layer can alter
    the definition of an existing field on the current layer using
    AlterFieldDefn(), otherwise FALSE.

    OLCDeleteFeature / "DeleteFeature": TRUE if the DeleteFeature()
    method is supported on this layer, otherwise FALSE.

    OLCStringsAsUTF8 / "StringsAsUTF8": TRUE if values of OFTString
    fields are assured to be in UTF-8 format. If FALSE the encoding of
    fields is uncertain, though it might still be UTF-8.

    OLCTransactions / "Transactions": TRUE if the StartTransaction(),
    CommitTransaction() and RollbackTransaction() methods work in a
    meaningful way, otherwise FALSE.

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

    Parameters:
    -----------

    hLayer:  handle to the layer to get the capability from.

    pszCap:  the name of the capability to test.

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

### CreateField(self, *args, **kwargs) | source code
    CreateField(self, FieldDefn field_def, int approx_ok = 1) -> OGRErr

    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 should not be called while there are feature objects in
    existance that were obtained or created with the previous layer
    definition.

    Not all drivers support this function. You can query a layer to check
    if it supports it with the OLCCreateField capability. Some drivers may
    only support this method while there are still no features in the
    layer. When it is supported, the existings features of the backing
    file/database should be updated accordingly.

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

    Parameters:
    -----------

    hLayer:  handle to the layer to write the field definition.

    hField:  handle of the field definition to write to disk.

    bApproxOK:  If TRUE, the field may be created in a slightly different
    form depending on the limitations of the format driver.

    OGRERR_NONE on success.

### DeleteField(self, *args) | source code
    DeleteField(self, int iField) -> OGRErr

    OGRErr
    OGR_L_DeleteField(OGRLayerH hLayer, int iField)

    Create a new field on a layer.

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

    This function should not be called while there are feature objects in
    existance that were obtained or created with the previous layer
    definition.

    Not all drivers support this function. You can query a layer to check
    if it supports it with the OLCDeleteField capability. Some drivers may
    only support this method while there are still no features in the
    layer. When it is supported, the existings features of the backing
    file/database should be updated accordingly.

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

    Parameters:
    -----------

    hLayer:  handle to the layer.

    iField:  index of the field to delete.

    OGRERR_NONE on success.

    OGR 1.9.0

### ReorderField(self, *args) | source code
    ReorderField(self, int iOldFieldPos, int iNewFieldPos) -> OGRErr

    OGRErr
    OGR_L_ReorderField(OGRLayerH hLayer, int iOldFieldPos, int
    iNewFieldPos)

    Reorder an existing field on a layer.

    This function is a conveniency wrapper of OGR_L_ReorderFields()
    dedicated to move a single field.

    You must use this to reorder existing fields on a real layer.
    Internally the OGRFeatureDefn for the layer will be updated to reflect
    the reordering of the fields. Applications should never modify the
    OGRFeatureDefn used by a layer directly.

    This function should not be called while there are feature objects in
    existance that were obtained or created with the previous layer
    definition.

    The field definition that was at initial position iOldFieldPos will be
    moved at position iNewFieldPos, and elements between will be shuffled
    accordingly.

    For example, let suppose the fields were "0","1","2","3","4"
    initially. ReorderField(1, 3) will reorder them as
    "0","2","3","1","4".

    Not all drivers support this function. You can query a layer to check
    if it supports it with the OLCReorderFields capability. Some drivers
    may only support this method while there are still no features in the
    layer. When it is supported, the existings features of the backing
    file/database should be updated accordingly.

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

    Parameters:
    -----------

    hLayer:  handle to the layer.

    iOldFieldPos:  previous position of the field to move. Must be in the
    range [0,GetFieldCount()-1].

    iNewFieldPos:  new position of the field to move. Must be in the range
    [0,GetFieldCount()-1].

    OGRERR_NONE on success.

    OGR 1.9.0

### ReorderFields(self, *args) | source code
    ReorderFields(self, int nList) -> OGRErr

    OGRErr
    OGR_L_ReorderFields(OGRLayerH hLayer, int *panMap)

    Reorder all the fields of a layer.

    You must use this to reorder existing fields on a real layer.
    Internally the OGRFeatureDefn for the layer will be updated to reflect
    the reordering of the fields. Applications should never modify the
    OGRFeatureDefn used by a layer directly.

    This function should not be called while there are feature objects in
    existance that were obtained or created with the previous layer
    definition.

    panMap is such that,for each field definition at position i after
    reordering, its position before reordering was panMap[i].

    For example, let suppose the fields were "0","1","2","3","4"
    initially. ReorderFields([0,2,3,1,4]) will reorder them as
    "0","2","3","1","4".

    Not all drivers support this function. You can query a layer to check
    if it supports it with the OLCReorderFields capability. Some drivers
    may only support this method while there are still no features in the
    layer. When it is supported, the existings features of the backing
    file/database should be updated accordingly.

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

    Parameters:
    -----------

    hLayer:  handle to the layer.

    panMap:  an array of GetLayerDefn()->GetFieldCount() elements which is
    a permutation of [0, GetLayerDefn()->GetFieldCount()-1].

    OGRERR_NONE on success.

    OGR 1.9.0

### AlterFieldDefn(self, *args) | source code
    AlterFieldDefn(self, int iField, FieldDefn field_def, int nFlags) -> OGRErr

    OGRErr
    OGR_L_AlterFieldDefn(OGRLayerH hLayer, int iField, OGRFieldDefnH
    hNewFieldDefn, int nFlags)

    Alter the definition of an existing field on a layer.

    You must use this to alter the definition of an existing field of a
    real layer. Internally the OGRFeatureDefn for the layer will be
    updated to reflect the altered field. Applications should never modify
    the OGRFeatureDefn used by a layer directly.

    This function should not be called while there are feature objects in
    existance that were obtained or created with the previous layer
    definition.

    Not all drivers support this function. You can query a layer to check
    if it supports it with the OLCAlterFieldDefn capability. Some drivers
    may only support this method while there are still no features in the
    layer. When it is supported, the existings features of the backing
    file/database should be updated accordingly. Some drivers might also
    not support all update flags.

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

    Parameters:
    -----------

    hLayer:  handle to the layer.

    iField:  index of the field whose definition must be altered.

    hNewFieldDefn:  new field definition

    nFlags:  combination of ALTER_NAME_FLAG, ALTER_TYPE_FLAG and
    ALTER_WIDTH_PRECISION_FLAG to indicate which of the name and/or type
    and/or width and precision fields from the new field definition must
    be taken into account.

    OGRERR_NONE on success.

    OGR 1.9.0

### StartTransaction(self) | source code
    OGRErr
    OGR_L_StartTransaction(OGRLayerH hLayer)

    For datasources which support transactions, StartTransaction creates a
    transaction.

    If starting the transaction fails, will return OGRERR_FAILURE.
    Datasources which do not support transactions will always return
    OGRERR_NONE.

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

    Parameters:
    -----------

    hLayer:  handle to the layer

    OGRERR_NONE on success.
Returns: OGRErr

### CommitTransaction(self) | source code
    OGRErr
    OGR_L_CommitTransaction(OGRLayerH hLayer)

    For datasources which support transactions, CommitTransaction commits
    a transaction.

    If no transaction is active, or the commit fails, will return
    OGRERR_FAILURE. Datasources which do not support transactions will
    always return OGRERR_NONE.

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

    Parameters:
    -----------

    hLayer:  handle to the layer

    OGRERR_NONE on success.
Returns: OGRErr

### RollbackTransaction(self) | source code
    OGRErr
    OGR_L_RollbackTransaction(OGRLayerH hLayer)

    For datasources which support transactions, RollbackTransaction will
    roll back a datasource to its state before the start of the current
    transaction. If no transaction is active, or the rollback fails, will
    return OGRERR_FAILURE. Datasources which do not support transactions
    will always return OGRERR_NONE.

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

    Parameters:
    -----------

    hLayer:  handle to the layer

    OGRERR_NONE on success.
Returns: OGRErr

### GetSpatialRef(self) | source code
    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().

    Parameters:
    -----------

    hLayer:  handle to the layer to get the spatial reference from.

    spatial reference, or NULL if there isn't one.
Returns: SpatialReference

### SetIgnoredFields(self, *args) | source code
    SetIgnoredFields(self, char options) -> OGRErr

    OGRErr
    OGR_L_SetIgnoredFields(OGRLayerH hLayer, const char **papszFields)

    Set which fields can be omitted when retrieving features from the
    layer.

    If the driver supports this functionality (testable using
    OLCIgnoreFields capability), it will not fetch the specified fields in
    subsequent calls to GetFeature() / GetNextFeature() and thus save some
    processing time and/or bandwidth.

    Besides field names of the layers, the following special fields can be
    passed: "OGR_GEOMETRY" to ignore geometry and "OGR_STYLE" to
    ignore layer style.

    By default, no fields are ignored.

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

    Parameters:
    -----------

    papszFields:  an array of field names terminated by NULL item. If NULL
    is passed, the ignored list is cleared.

    OGRERR_NONE if all field names have been resolved (even if the driver
    does not support this method)

### __getitem__(self, value) (Indexing operator) | source code
Support list and slice -like access to the layer. r[0] would return the first feature on the layer. r[0:4] would return a list of the first four features.