OGRDataSource *poDS;
poDS = OGRSFDriverRegistrar::Open( "polygon.shp" );
if( poDS == NULL )
{
return;
}
... use the data source ...
delete poDS;
*/
/**
\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.
@param poDriver the driver to add.
*/
/**
\fn int OGRSFDriverRegistrar::GetDriverCount();
Fetch the number of registered drivers.
@return the driver count.
*/
/**
\fn OGRSFDriver * OGRSFDriverRegistrar::GetDriver( int iDriver );
Fetch the indicated driver.
@param iDriver the driver index, from 0 to GetDriverCount()-1.
@return pointer to the driver, or NULL if iDriver is out of range.
*/
/************************************************************************/
/* 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".
@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.
@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.
*/
/************************************************************************/
/* 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.
@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.
@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.
@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.
*/
/************************************************************************/
/* OGRLayer */
/************************************************************************/
/**
\fn void OGRLayer::ResetReading();
Reset feature reading to start on the first feature. This affects
GetNextFeature().
*/
/**
\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.
@return 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.
@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.
@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.
@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 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.
@return 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()).
@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.
@return 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.
@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 filter.
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 random access reading via GetFeature().
@param nFID the feature id of the feature to read.
@return 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().
@param poFeature 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.
@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.
*/ /** \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. @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. */