GDALDataset Class Reference

A set of associated raster bands, usually from one file. More...

#include <gdal_priv.h>

Inheritance diagram for GDALDataset:

List of all members.

Public Member Functions
virtual	~GDALDataset ()
int	GetRasterXSize (void)
int	GetRasterYSize (void)
int	GetRasterCount (void)
GDALRasterBand *	GetRasterBand (int)
virtual void	FlushCache (void)
virtual const char *	GetProjectionRef (void)
virtual CPLErr	SetProjection (const char *)
virtual CPLErr	GetGeoTransform (double *)
virtual CPLErr	SetGeoTransform (double *)
virtual CPLErr	AddBand (GDALDataType eType, char **papszOptions=NULL)
virtual void *	GetInternalHandle (const char *)
virtual GDALDriver *	GetDriver (void)
virtual char **	GetFileList (void)
virtual int	GetGCPCount ()
virtual const char *	GetGCPProjection ()
virtual const GDAL_GCP *	GetGCPs ()
virtual CPLErr	SetGCPs (int nGCPCount, const GDAL_GCP *pasGCPList, const char *pszGCPProjection)
virtual CPLErr	AdviseRead (int nXOff, int nYOff, int nXSize, int nYSize, int nBufXSize, int nBufYSize, GDALDataType eDT, int nBandCount, int *panBandList, char **papszOptions)
virtual CPLErr	CreateMaskBand (int nFlags)
CPLErr	RasterIO (GDALRWFlag, int, int, int, int, void *, int, int, GDALDataType, int, int *, int, int, int)
int	Reference ()
int	Dereference ()
GDALAccess	GetAccess ()
int	GetShared ()
void	MarkAsShared ()
CPLErr	BuildOverviews (const char *, int, int *, int, int *, GDALProgressFunc, void *)
Static Public Member Functions
static GDALDataset **	GetOpenDatasets (int *pnDatasetCount)
Protected Member Functions
void	RasterInitialize (int, int)
void	SetBand (int, GDALRasterBand *)
virtual CPLErr	IBuildOverviews (const char *, int, int *, int, int *, GDALProgressFunc, void *)
virtual CPLErr	IRasterIO (GDALRWFlag, int, int, int, int, void *, int, int, GDALDataType, int, int *, int, int, int)
CPLErr	BlockBasedRasterIO (GDALRWFlag, int, int, int, int, void *, int, int, GDALDataType, int, int *, int, int, int)
void	BlockBasedFlushCache ()
Protected Attributes
GDALDriver *	poDriver
GDALAccess	eAccess
int	nRasterXSize
int	nRasterYSize
int	nBands
GDALRasterBand **	papoBands
int	bForceCachedIO
int	nRefCount
int	bShared
GDALDefaultOverviews	oOvManager
Friends
class	GDALDriver
class	GDALDefaultOverviews
class	GDALProxyDataset
class	GDALRasterBand
GDALDatasetH	GDALOpen (const char *, GDALAccess)
GDALDatasetH	GDALOpenShared (const char *, GDALAccess)

---

Detailed Description

A set of associated raster bands, usually from one file.

A dataset encapsulating one or more raster bands. Details are further discussed in the GDAL Data Model.

Use GDALOpen() or GDALOpenShared() to create a GDALDataset for a named file, or GDALDriver::Create() or GDALDriver::CreateCopy() to create a new dataset.

---

Constructor & Destructor Documentation

GDALDataset::~GDALDataset

(

)

[virtual]

Destroy an open GDALDataset.

This is the accepted method of closing a GDAL dataset and deallocating all resources associated with it.

Equivelent of the C callable GDALClose(). Except that GDALClose() first decrements the reference count, and then closes only if it has dropped to zero.

References GDALMajorObject::GetDescription().

---

Member Function Documentation

CPLErr GDALDataset::AddBand	(	GDALDataType	eType,
		char **	papszOptions = NULL
	)			[virtual]

Add a band to a dataset.

This method will add a new band to the dataset if the underlying format supports this action. Most formats do not.

Note that the new GDALRasterBand is not returned. It may be fetched after successful completion of the method by calling GDALDataset::GetRasterBand(GDALDataset::GetRasterCount()-1) as the newest band will always be the last band.

Parameters:

	eType	the data type of the pixels in the new band.
	papszOptions	a list of NAME=VALUE option strings. The supported options are format specific. NULL may be passed by default.

Returns:

CE_None on success or CE_Failure on failure.

Reimplemented in VRTDataset, and VRTWarpedDataset.

CPLErr GDALDataset::AdviseRead	(	int	nXOff,
		int	nYOff,
		int	nXSize,
		int	nYSize,
		int	nBufXSize,
		int	nBufYSize,
		GDALDataType	eDT,
		int	nBandCount,
		int *	panBandMap,
		char **	papszOptions
	)			[virtual]

Advise driver of upcoming read requests.

Some GDAL drivers operate more efficiently if they know in advance what set of upcoming read requests will be made. The AdviseRead() method allows an application to notify the driver of the region and bands of interest, and at what resolution the region will be read.

Many drivers just ignore the AdviseRead() call, but it can dramatically accelerate access via some drivers.

Parameters:

	nXOff	The pixel offset to the top left corner of the region of the band to be accessed. This would be zero to start from the left side.
	nYOff	The line offset to the top left corner of the region of the band to be accessed. This would be zero to start from the top.
	nXSize	The width of the region of the band to be accessed in pixels.
	nYSize	The height of the region of the band to be accessed in lines.
	nBufXSize	the width of the buffer image into which the desired region is to be read, or from which it is to be written.
	nBufYSize	the height of the buffer image into which the desired region is to be read, or from which it is to be written.
	eBufType	the type of the pixel values in the pData data buffer. The pixel values will automatically be translated to/from the GDALRasterBand data type as needed.
	nBandCount	the number of bands being read or written.
	panBandMap	the list of nBandCount band numbers being read/written. Note band numbers are 1 based. This may be NULL to select the first nBandCount bands.
	papszOptions	a list of name=value strings with special control options. Normally this is NULL.

Returns:

CE_Failure if the request is invalid and CE_None if it works or is ignored.

Reimplemented in GDALProxyDataset.

References GDALRasterBand::AdviseRead(), and GetRasterBand().

CPLErr GDALDataset::BuildOverviews	(	const char *	pszResampling,
		int	nOverviews,
		int *	panOverviewList,
		int	nListBands,
		int *	panBandList,
		GDALProgressFunc	pfnProgress,
		void *	pProgressData
	)

Build raster overview(s)

If the operation is unsupported for the indicated dataset, then CE_Failure is returned, and CPLGetLastErrorNo() will return CPLE_NotSupported.

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

Parameters:

	pszResampling	one of "NEAREST", "GAUSS", "AVERAGE", "AVERAGE_MAGPHASE" or "NONE" controlling the downsampling method applied.
	nOverviews	number of overviews to build.
	panOverviewList	the list of overview decimation factors to build.
	nBand	number of bands to build overviews for in panBandList. Build for all bands if this is 0.
	panBandList	list of band numbers.
	pfnProgress	a function to call to report progress, or NULL.
	pProgressData	application data to pass to the progress function.

Returns:

CE_None on success or CE_Failure if the operation doesn't work.

For example, to build overview level 2, 4 and 8 on all bands the following call could be made:

   int       anOverviewList[3] = { 2, 4, 8 };

   poDataset->BuildOverviews( "NEAREST", 3, anOverviewList, 0, NULL, 
                              GDALDummyProgress, NULL );
 

See also:

GDALRegenerateOverviews()

References GetRasterCount().

int GDALDataset::Dereference

(

)

Subtract one from dataset reference count.

The reference is one after instantiation. Generally when the reference count has dropped to zero the dataset may be safely deleted (closed).

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

Returns:

the post-decrement reference count.

Referenced by GDALClose().

void GDALDataset::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.

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

Reimplemented in GDALPamDataset, GDALProxyDataset, and VRTDataset.

References GDALRasterBand::FlushCache().

Referenced by GDALProxyDataset::FlushCache().

GDALDriver * GDALDataset::GetDriver

(

void

)

[virtual]

Fetch the driver to which this dataset relates.

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

Returns:

the driver on which the dataset was created with GDALOpen() or GDALCreate().

Reimplemented in GDALProxyDataset.

char ** GDALDataset::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.

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

Returns:

NULL or a NULL terminated array of file names.

Reimplemented in GDALPamDataset, and GDALProxyDataset.

References GDALMajorObject::GetDescription(), GetFileList(), and VSIStatL().

Referenced by GetFileList().

int GDALDataset::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 in GDALPamDataset, GDALProxyDataset, and VRTDataset.

Referenced by GDALProxyPoolDataset::GetGCPs().

const char * GDALDataset::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.

Reimplemented in GDALPamDataset, GDALProxyDataset, GDALProxyPoolDataset, and VRTDataset.

Referenced by GDALProxyPoolDataset::GetGCPProjection().

const GDAL_GCP * GDALDataset::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 in GDALPamDataset, GDALProxyDataset, GDALProxyPoolDataset, and VRTDataset.

Referenced by GDALProxyPoolDataset::GetGCPs().

CPLErr GDALDataset::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 in GDALPamDataset, GDALProxyDataset, GDALProxyPoolDataset, and VRTDataset.

void * GDALDataset::GetInternalHandle

(

const char *

)

[virtual]

Fetch a format specific internally meaningful handle.

This method is the same as the C GDALGetInternalHandle() method.

Parameters:

pszHandleName

the handle name desired. The meaningful names will be specific to the file format.

Returns:

the desired handle value, or NULL if not recognised/supported.

Reimplemented in GDALProxyDataset, and GDALProxyPoolDataset.

GDALDataset ** GDALDataset::GetOpenDatasets

(

int *

pnCount

)

[static]

Fetch all open GDAL dataset handles.

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

NOTE: This method is not thread safe. The returned list may changed at any time.

Parameters:

pnCount

integer into which to place the count of dataset pointers being returned.

Returns:

a pointer to an array of dataset handles.

Referenced by GDALGetOpenDatasets().

const char * GDALDataset::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 in GDALPamDataset, GDALProxyDataset, GDALProxyPoolDataset, and VRTDataset.

GDALRasterBand * GDALDataset::GetRasterBand

(

int

nBandId

)

Fetch a band object for a dataset.

Equivelent of the C function GDALGetRasterBand().

Parameters:

nBandId

the index number of the band to fetch, from 1 to GetRasterCount().

Returns:

the height in pixels of raster bands in this GDALDataset.

Referenced by AdviseRead(), GDALCreateWarpedVRT(), GDALDatasetCopyWholeRaster(), GDALRasterizeGeometries(), VRTWarpedRasterBand::GetOverview(), and RasterIO().

int GDALDataset::GetRasterCount

(

void

)

Fetch the number of raster bands on this dataset.

Same as the C function GDALGetRasterCount().

Returns:

the number of raster bands.

Referenced by VRTWarpedDataset::AddBand(), VRTDataset::AddBand(), BuildOverviews(), GDALDatasetCopyWholeRaster(), GDALRegenerateOverviews(), and RasterIO().

int GDALDataset::GetRasterXSize

(

void

)

Fetch raster width in pixels.

Equivelent of the C function GDALGetRasterXSize().

Returns:

the width in pixels of raster bands in this GDALDataset.

Referenced by VRTDataset::AddBand(), GDALDatasetCopyWholeRaster(), and GDALRasterizeGeometries().

int GDALDataset::GetRasterYSize

(

void

)

Fetch raster height in pixels.

Equivelent of the C function GDALGetRasterYSize().

Returns:

the height in pixels of raster bands in this GDALDataset.

Referenced by VRTDataset::AddBand(), GDALDatasetCopyWholeRaster(), and GDALRasterizeGeometries().

int GDALDataset::GetShared

(

)

Returns shared flag.

Returns:

TRUE if the GDALDataset is available for sharing, or FALSE if not.

Referenced by GDALClose().

void GDALDataset::MarkAsShared

(

)

Mark this dataset as available for sharing.

References GDALMajorObject::GetDescription().

Referenced by GDALOpenShared().

CPLErr GDALDataset::RasterIO	(	GDALRWFlag	eRWFlag,
		int	nXOff,
		int	nYOff,
		int	nXSize,
		int	nYSize,
		void *	pData,
		int	nBufXSize,
		int	nBufYSize,
		GDALDataType	eBufType,
		int	nBandCount,
		int *	panBandMap,
		int	nPixelSpace,
		int	nLineSpace,
		int	nBandSpace
	)

Read/write a region of image data from multiple bands.

This method allows reading a region of one or more GDALRasterBands from this dataset into a buffer, or writing data from a buffer into a region of the GDALRasterBands. It automatically takes care of data type translation if the data type (eBufType) of the buffer is different than that of the GDALRasterBand. The method also takes care of image decimation / replication if the buffer size (nBufXSize x nBufYSize) is different than the size of the region being accessed (nXSize x nYSize).

The nPixelSpace, nLineSpace and nBandSpace parameters allow reading into or writing from various organization of buffers.

For highest performance full resolution data access, read and write on "block boundaries" as returned by GetBlockSize(), or use the ReadBlock() and WriteBlock() methods.

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

Parameters:

	eRWFlag	Either GF_Read to read a region of data, or GF_Write to write a region of data.
	nXOff	The pixel offset to the top left corner of the region of the band to be accessed. This would be zero to start from the left side.
	nYOff	The line offset to the top left corner of the region of the band to be accessed. This would be zero to start from the top.
	nXSize	The width of the region of the band to be accessed in pixels.
	nYSize	The height of the region of the band to be accessed in lines.
	pData	The buffer into which the data should be read, or from which it should be written. This buffer must contain at least nBufXSize * nBufYSize * nBandCount words of type eBufType. It is organized in left to right,top to bottom pixel order. Spacing is controlled by the nPixelSpace, and nLineSpace parameters.
	nBufXSize	the width of the buffer image into which the desired region is to be read, or from which it is to be written.
	nBufYSize	the height of the buffer image into which the desired region is to be read, or from which it is to be written.
	eBufType	the type of the pixel values in the pData data buffer. The pixel values will automatically be translated to/from the GDALRasterBand data type as needed.
	nBandCount	the number of bands being read or written.
	panBandMap	the list of nBandCount band numbers being read/written. Note band numbers are 1 based. This may be NULL to select the first nBandCount bands.
	nPixelSpace	The byte offset from the start of one pixel value in pData to the start of the next pixel value within a scanline. If defaulted (0) the size of the datatype eBufType is used.
	nLineSpace	The byte offset from the start of one scanline in pData to the start of the next. If defaulted the size of the datatype eBufType * nBufXSize is used.
	nBandSpace	the byte offset from the start of one bands data to the start of the next. If defaulted (zero) the value will be nLineSpace * nBufYSize implying band sequential organization of the data buffer.

Returns:

CE_Failure if the access fails, otherwise CE_None.

References GDALGetDataTypeSize(), GetRasterBand(), GetRasterCount(), GF_Read, and GF_Write.

Referenced by GDALDatasetCopyWholeRaster(), GDALDatasetRasterIO(), and GDALRasterizeGeometries().

int GDALDataset::Reference

(

)

Add one to dataset reference count.

The reference is one after instantiation.

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

Returns:

the post-increment reference count.

Referenced by GDALOpenShared().

CPLErr GDALDataset::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 in GDALPamDataset, GDALProxyDataset, and VRTDataset.

CPLErr GDALDataset::SetGeoTransform

(

double *

)

[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 in GDALPamDataset, GDALProxyDataset, GDALProxyPoolDataset, and VRTDataset.

CPLErr GDALDataset::SetProjection

(

const char *

)

[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 in GDALPamDataset, GDALProxyDataset, GDALProxyPoolDataset, and VRTDataset.

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Friends And Related Function Documentation

GDALDatasetH GDALOpen	(	const char *	pszFilename,
		GDALAccess	eAccess
	)			[friend]

Open a raster file as a GDALDataset.

This function will try to open the passed file, or virtual dataset name by invoking the Open method of each registered GDALDriver in turn. The first successful open will result in a returned dataset. If all drivers fail then NULL is returned.

Several recommandations :

• If you open a dataset object with GA_Update access, it is not recommanded to open a new dataset on the same underlying file.
• The returned dataset should only be accessed by one thread at a time. If you want to use it from different threads, you must add all necessary code (mutexes, etc.) to avoid concurrent use of the object. (Some drivers, such as GeoTIFF, maintain internal state variables that are updated each time a new block is read, thus preventing concurrent use.)

See also:

GDALOpenShared()

Parameters:

	pszFilename	the name of the file to access. In the case of exotic drivers this may not refer to a physical file, but instead contain information for the driver on how to access a dataset.
	eAccess	the desired access, either GA_Update or GA_ReadOnly. Many drivers support only read only access.

Returns:

A GDALDatasetH handle or NULL on failure. For C++ applications this handle can be cast to a GDALDataset *.

GDALDatasetH GDALOpenShared	(	const char *	pszFilename,
		GDALAccess	eAccess
	)			[friend]

Open a raster file as a GDALDataset.

This function works the same as GDALOpen(), but allows the sharing of GDALDataset handles for a dataset with other callers to GDALOpenShared().

In particular, GDALOpenShared() will first consult it's list of currently open and shared GDALDataset's, and if the GetDescription() name for one exactly matches the pszFilename passed to GDALOpenShared() it will be referenced and returned.

Starting with GDAL 1.6.0, if GDALOpenShared() is called on the same pszFilename from two different threads, a different GDALDataset object will be returned as it is not safe to use the same dataset from different threads, unless the user does explicitely use mutexes in its code.

See also:

GDALOpen()

Parameters:

	pszFilename	the name of the file to access. In the case of exotic drivers this may not refer to a physical file, but instead contain information for the driver on how to access a dataset.
	eAccess	the desired access, either GA_Update or GA_ReadOnly. Many drivers support only read only access.

Returns:

A GDALDatasetH handle or NULL on failure. For C++ applications this handle can be cast to a GDALDataset *.

---

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

• gdal_priv.h
• gdaldataset.cpp
• rasterio.cpp