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GDALPamDataset Class Reference

PAM dataset. More...

#include <gdal_pam.h>

Inheritance diagram for GDALPamDataset:
GDALDataset GDALMajorObject

Public Member Functions

virtual void FlushCache (void) CPL_OVERRIDE
 Flush all write cached data to disk. More...
 
virtual const char * GetProjectionRef (void) CPL_OVERRIDE
 Fetch the projection definition string for this dataset. More...
 
virtual CPLErr SetProjection (const char *) CPL_OVERRIDE
 Set the projection reference string for this dataset. More...
 
virtual CPLErr GetGeoTransform (double *) CPL_OVERRIDE
 Fetch the affine transformation coefficients. More...
 
virtual CPLErr SetGeoTransform (double *) CPL_OVERRIDE
 Set the affine transformation coefficients. More...
 
virtual int GetGCPCount () CPL_OVERRIDE
 Get number of GCPs. More...
 
virtual const char * GetGCPProjection () CPL_OVERRIDE
 Get output projection for GCPs. More...
 
virtual const GDAL_GCPGetGCPs () CPL_OVERRIDE
 Fetch GCPs. More...
 
virtual CPLErr SetGCPs (int nGCPCount, const GDAL_GCP *pasGCPList, const char *pszGCPProjection) CPL_OVERRIDE
 Assign GCPs. More...
 
virtual CPLErr SetMetadata (char **papszMetadata, const char *pszDomain="") CPL_OVERRIDE
 Set metadata. More...
 
virtual CPLErr SetMetadataItem (const char *pszName, const char *pszValue, const char *pszDomain="") CPL_OVERRIDE
 Set single metadata item. More...
 
virtual char ** GetMetadata (const char *pszDomain="") CPL_OVERRIDE
 Fetch metadata. More...
 
virtual const char * GetMetadataItem (const char *pszName, const char *pszDomain="") CPL_OVERRIDE
 Fetch single metadata item. More...
 
virtual char ** GetFileList (void) CPL_OVERRIDE
 Fetch files forming dataset. More...
 
- Public Member Functions inherited from GDALDataset
virtual ~GDALDataset ()
 Destroy an open GDALDataset. More...
 
int GetRasterXSize (void)
 Fetch raster width in pixels. More...
 
int GetRasterYSize (void)
 Fetch raster height in pixels. More...
 
int GetRasterCount (void)
 Fetch the number of raster bands on this dataset. More...
 
GDALRasterBandGetRasterBand (int)
 Fetch a band object for a dataset. More...
 
virtual CPLErr AddBand (GDALDataType eType, char **papszOptions=NULL)
 Add a band to a dataset. More...
 
virtual void * GetInternalHandle (const char *pszHandleName)
 Fetch a format specific internally meaningful handle. More...
 
virtual GDALDriverGetDriver (void)
 Fetch the driver to which this dataset relates. More...
 
virtual const char * GetDriverName ()
 Return driver name. More...
 
virtual CPLErr AdviseRead (int nXOff, int nYOff, int nXSize, int nYSize, int nBufXSize, int nBufYSize, GDALDataType eDT, int nBandCount, int *panBandList, char **papszOptions)
 Advise driver of upcoming read requests. More...
 
virtual CPLErr CreateMaskBand (int nFlagsIn)
 Adds a mask band to the dataset. More...
 
virtual GDALAsyncReaderBeginAsyncReader (int nXOff, int nYOff, int nXSize, int nYSize, void *pBuf, int nBufXSize, int nBufYSize, GDALDataType eBufType, int nBandCount, int *panBandMap, int nPixelSpace, int nLineSpace, int nBandSpace, char **papszOptions)
 Sets up an asynchronous data request. More...
 
virtual void EndAsyncReader (GDALAsyncReader *)
 End asynchronous request. More...
 
CPLErr RasterIO (GDALRWFlag, int, int, int, int, void *, int, int, GDALDataType, int, int *, GSpacing, GSpacing, GSpacing, GDALRasterIOExtraArg *psExtraArg) CPL_WARN_UNUSED_RESULT
 Read/write a region of image data from multiple bands. More...
 
int Reference ()
 Add one to dataset reference count. More...
 
int Dereference ()
 Subtract one from dataset reference count. More...
 
GDALAccess GetAccess () const
 Return access mode. More...
 
int GetShared () const
 Returns shared flag. More...
 
void MarkAsShared ()
 Mark this dataset as available for sharing.
 
void MarkSuppressOnClose ()
 Set that the dataset must be deleted on close. More...
 
char ** GetOpenOptions ()
 Return open options. More...
 
CPLErr BuildOverviews (const char *, int, int *, int, int *, GDALProgressFunc, void *)
 Build raster overview(s) More...
 
void ReportError (CPLErr eErrClass, CPLErrorNum err_no, const char *fmt,...) CPL_PRINT_FUNC_FORMAT(4
 Emits an error related to a dataset. More...
 
virtual char ** GetMetadataDomainList () CPL_OVERRIDE
 Fetch list of metadata domains. More...
 
virtual int GetLayerCount ()
 Get the number of layers in this dataset. More...
 
virtual OGRLayerGetLayer (int iLayer)
 Fetch a layer by index. More...
 
virtual OGRLayerGetLayerByName (const char *)
 Fetch a layer by name. More...
 
virtual OGRErr DeleteLayer (int iLayer)
 Delete the indicated layer from the datasource. More...
 
virtual void ResetReading ()
 Reset feature reading to start on the first feature. More...
 
virtual OGRFeatureGetNextFeature (OGRLayer **ppoBelongingLayer, double *pdfProgressPct, GDALProgressFunc pfnProgress, void *pProgressData)
 Fetch the next available feature from this dataset. More...
 
virtual int TestCapability (const char *)
 Test if capability is available. More...
 
virtual OGRLayerCreateLayer (const char *pszName, OGRSpatialReference *poSpatialRef=NULL, OGRwkbGeometryType eGType=wkbUnknown, char **papszOptions=NULL)
 This method attempts to create a new layer on the dataset with the indicated name, coordinate system, geometry type. More...
 
virtual OGRLayerCopyLayer (OGRLayer *poSrcLayer, const char *pszNewName, char **papszOptions=NULL)
 Duplicate an existing layer. More...
 
virtual OGRStyleTableGetStyleTable ()
 Returns dataset style table. More...
 
virtual void SetStyleTableDirectly (OGRStyleTable *poStyleTable)
 Set dataset style table. More...
 
virtual void SetStyleTable (OGRStyleTable *poStyleTable)
 Set dataset style table. More...
 
virtual OGRLayerExecuteSQL (const char *pszStatement, OGRGeometry *poSpatialFilter, const char *pszDialect)
 Execute an SQL statement against the data store. More...
 
virtual void ReleaseResultSet (OGRLayer *poResultsSet)
 Release results of ExecuteSQL(). More...
 
int GetRefCount () const
 Fetch reference count. More...
 
int GetSummaryRefCount () const
 Fetch reference count of datasource and all owned layers. More...
 
OGRErr Release ()
 Drop a reference to this dataset, and if the reference count drops to one close (destroy) the dataset. More...
 
virtual OGRErr StartTransaction (int bForce=FALSE)
 For datasources which support transactions, StartTransaction creates a `transaction. More...
 
virtual OGRErr CommitTransaction ()
 For datasources which support transactions, CommitTransaction commits a transaction. More...
 
virtual OGRErr RollbackTransaction ()
 For datasources which support transactions, RollbackTransaction will roll back a datasource to its state before the start of the current transaction. More...
 
- Public Member Functions inherited from GDALMajorObject
int GetMOFlags () const
 Returns the GMO_ flags. More...
 
void SetMOFlags (int nFlagsIn)
 Assign GMO_flags. More...
 
virtual const char * GetDescription () const
 Fetch object description. More...
 
virtual void SetDescription (const char *)
 Set object description. More...
 

Friends

class GDALPamRasterBand
 

Additional Inherited Members

- Static Public Member Functions inherited from GDALDataset
static GDALDataset ** GetOpenDatasets (int *pnDatasetCount)
 Fetch all open GDAL dataset handles. More...
 
- Protected Member Functions inherited from GDALDataset
virtual int CloseDependentDatasets ()
 Drop references to any other datasets referenced by this dataset. More...
 
virtual OGRLayerICreateLayer (const char *pszName, OGRSpatialReference *poSpatialRef=NULL, OGRwkbGeometryType eGType=wkbUnknown, char **papszOptions=NULL)
 This method attempts to create a new layer on the dataset with the indicated name, coordinate system, geometry type. More...
 
- Protected Member Functions inherited from GDALMajorObject
char ** BuildMetadataDomainList (char **papszList, int bCheckNonEmpty,...) CPL_NULL_TERMINATED
 Helper function for custom implementations of GetMetadataDomainList() More...
 

Detailed Description

PAM dataset.

A subclass of GDALDataset which introduces the ability to save and restore auxiliary information (coordinate system, gcps, metadata, etc) not supported by a file format via an "auxiliary 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 dependent and defaults to YES in Windows and Unix builds.

PAM Proxy Files

In order to be able to record auxiliary 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 auxiliary 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,"") )
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.

The default implementation of this method just calls the FlushCache() method on each of the raster bands and the SyncToDisk() method on each of the layers. Conceptionally, calling FlushCache() on a dataset should include any work that might be accomplished by calling SyncToDisk() on layers in that dataset.

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.

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.

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.

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.

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.

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.

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

Parameters
padfTransforman 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.

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 formatted as a "Name=value" list with the last pointer value being NULL. Use 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
pszDomainthe domain of interest. Use "" or NULL for the default domain.
Returns
NULL or a string list.

Reimplemented from GDALDataset.

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
pszNamethe key for the metadata item to fetch.
pszDomainthe 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 GDALDataset.

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/osr_tutorial.html

Reimplemented from GDALDataset.

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 responsible for deallocating these arguments if appropriate.

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

Parameters
nGCPCountnumber of GCPs being assigned.
pasGCPListarray of GCP structures being assign (nGCPCount in array).
pszGCPProjectionthe 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.

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
padfTransforma 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.

CPLErr GDALPamDataset::SetMetadata ( char **  papszMetadata,
const char *  pszDomain = "" 
)
virtual

Set metadata.

CAUTION: depending on the format, older values of the updated information might still be found in the file in a "ghost" state, even if no longer accessible through the GDAL API. This is for example the case of the GTiff format (this is not a exhaustive list)

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

Parameters
papszMetadatathe metadata in name=value string list format to apply.
pszDomainthe 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 GDALDataset.

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

Set single metadata item.

CAUTION: depending on the format, older values of the updated information might still be found in the file in a "ghost" state, even if no longer accessible through the GDAL API. This is for example the case of the GTiff format (this is not a exhaustive list)

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

Parameters
pszNamethe key for the metadata item to fetch.
pszValuethe value to assign to the key.
pszDomainthe domain to set within, use NULL for the default domain.
Returns
CE_None on success, or an error code on failure.

Reimplemented from GDALDataset.

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
pszProjectionprojection reference string.
Returns
CE_Failure if an error occurs, otherwise CE_None.

Reimplemented from GDALDataset.


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

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