缘起
GDAL的栅格化算法中有GDALRasterizeLayers、GDALRasterizeLayersBuf和GDALRasterizeGeometries函数，但是没有GDALRasterizeGeometriesBuf函数（GDAL项目不打算添加这个函数，因为增加一个函数会增加维护成本）。而栅格化算法的实际实现函数gv_rasterize_one_shape并不导出，所以在使用的时候造成了一定的不便。
虽然可以通过MEMDataset的方式，调用GDALRasterizeGeometries达到目的，但是不够直接和高效，所以我写了GDALRasterizeGeometriesBuf函数。
个人认为比较灵活的方式，还是将gv_rasterize_one_shape函数导出，以便自由使用。
代码
修改gdal/alg/gdal_alg.h头文件，在GDALRasterizeGeometries函数声明下添加GDALRasterizeGeometriesBuf函数声明。
CPLErr CPL_DLL
GDALRasterizeGeometriesBuf( void *pData, int nBufXSize, int nBufYSize,
GDALDataType eBufType, int nPixelSpace, int nLineSpace,
int nGeomCount, OGRGeometryH *pahGeometries,
const char *pszGeomProjection,
const char *pszDstProjection,
double *padfDstGeoTransform,
GDALTransformerFunc pfnTransformer,
void *pTransformArg, double dfBurnValue,
char **papszOptions, GDALProgressFunc pfnProgress,
void *pProgressArg );
修改gdal/alg/gdalrasterize.cpp文件，添加GDALRasterizeGeometriesBuf函数的实现，代码如下：
/************************************************************************/
/* GDALRasterizeGeometriesBuf() */
/************************************************************************/
/**
* Burn geometries into raster.
*
* Rasterize a list of geometric objects into a raster dataset. The
* geometries are passed as an array of OGRGeometryH handlers.
*
* If the geometries are in the georeferenced coordinates of the raster
* dataset, then the pfnTransform may be passed in NULL and one will be
* derived internally from the geotransform of the dataset. The transform
* needs to transform the geometry locations into pixel/line coordinates
* of the target raster.
*
* The output raster may be of any GDAL supported datatype, though currently
* internally the burning is done either as GDT_Byte or GDT_Float32. This
* may be improved in the future.
*
* @param pData pointer to the output data array.
* @param nBufXSize width of the output data array in pixels.
* @param nBufYSize height of the output data array in pixels.
* @param eBufType data type of the output data array.
*
* @param 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.
*
* @param 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.
*
* @param nGeomCount the number of geometries being passed in pahGeometries.
* @param pahGeometries the array of geometries to burn in.
* @param pszGeomProjection WKT defining the coordinate system of the geometries.
*
* @param pszDstProjection WKT defining the coordinate system of the target
* raster.
*
* @param padfDstGeoTransform geotransformation matrix of the target raster.
*
* @param pfnTransformer transformation to apply to geometries to put into
* pixel/line coordinates on raster. If NULL a geotransform based one will
* be created internally.
*
* @param pTransformArg callback data for transformer.
* @param dfBurnValue the value to burn into the raster.
*
* @param papszOptions special options controlling rasterization:
* <ul>
* <li>"ALL_TOUCHED": May be set to TRUE to set all pixels touched
* by the line or polygons, not just those whose center is within the polygon
* or that are selected by brezenhams line algorithm. Defaults to FALSE.</li>
* <li>"BURN_VALUE_FROM": May be set to "Z" to use
* the Z values of the geometries. dfBurnValue or the attribute field value is
* added to this before burning. In default case dfBurnValue is burned as it
* is. This is implemented properly only for points and lines for now. Polygons
* will be burned using the Z value from the first point. The M value may
* be supported in the future.</li>
* <li>"MERGE_ALG": May be REPLACE (the default) or ADD. REPLACE
* results in overwriting of value, while ADD adds the new value to the
* existing raster, suitable for heatmaps for instance.</li>
* </ul>
*
* @param pfnProgress the progress function to report completion.
*
* @param pProgressArg callback data for progress function.
*
*
* @return CE_None on success or CE_Failure on error.
*/
CPLErr GDALRasterizeGeometriesBuf( void *pData, int nBufXSize, int nBufYSize,
GDALDataType eBufType, int nPixelSpace, int nLineSpace,
int nGeomCount, OGRGeometryH *pahGeometries,
const char *pszGeomProjection,
const char *pszDstProjection,
double *padfDstGeoTransform,
GDALTransformerFunc pfnTransformer,
void *pTransformArg, double dfBurnValue,
char **papszOptions, GDALProgressFunc pfnProgress,
void *pProgressArg )
{
/* -------------------------------------------------------------------- */
/* If pixel and line spaceing are defaulted assign reasonable */
/* value assuming a packed buffer. */
/* -------------------------------------------------------------------- */
if( nPixelSpace != 0 )
{
nPixelSpace = GDALGetDataTypeSizeBytes( eBufType );
}
if( nPixelSpace != GDALGetDataTypeSizeBytes( eBufType ) )
{
CPLError(CE_Failure, CPLE_NotSupported,
"GDALRasterizeGeometriesBuf(): unsupported value of nPixelSpace");
return CE_Failure;
}
if( nLineSpace == 0 )
{
nLineSpace = nPixelSpace * nBufXSize;
}
if( nLineSpace != nPixelSpace * nBufXSize )
{
CPLError(CE_Failure, CPLE_NotSupported,
"GDALRasterizeGeometriesBuf(): unsupported value of nLineSpace");
return CE_Failure;
}
if( pfnProgress == nullptr )
pfnProgress = GDALDummyProgress;
/* -------------------------------------------------------------------- */
/* Do some rudimentary arg checking. */
/* -------------------------------------------------------------------- */
if( nGeomCount == 0 )
return CE_None;
/* -------------------------------------------------------------------- */
/* Options */
/* -------------------------------------------------------------------- */
int bAllTouched = FALSE;
GDALBurnValueSrc eBurnValueSource = GBV_UserBurnValue;
GDALRasterMergeAlg eMergeAlg = GRMA_Replace;
GDALRasterizeOptim eOptim = GRO_Auto;
if( GDALRasterizeOptions(papszOptions, &bAllTouched,
&eBurnValueSource, &eMergeAlg,
&eOptim) == CE_Failure )
{
return CE_Failure;
}
/* -------------------------------------------------------------------- */
/* If we have no transformer, create the one from input file */
/* projection. Note that each layer can be georefernced */
/* separately. */
/* -------------------------------------------------------------------- */
bool bNeedToFreeTransformer = false;
if( pfnTransformer == nullptr )
{
if( !pszGeomProjection )
{
CPLError( CE_Warning, CPLE_AppDefined,
"There is no specified spatial reference for the"
" geometry to build transformer, assuming"
" matching coordinate systems.");
}
pTransformArg =
GDALCreateGenImgProjTransformer3( pszGeomProjection, nullptr,
pszDstProjection,
padfDstGeoTransform );
pfnTransformer = GDALGenImgProjTransform;
}
/* ==================================================================== */
/* Write geometry to the raster individually. */
/* ==================================================================== */
CPLErr eErr = CE_None;
pfnProgress( 0.0, nullptr, pProgressArg );
int iGeometry;
for(iGeometry = 0; iGeometry < nGeomCount; ++iGeometry )
{
OGRGeometry *poGeom = reinterpret_cast<OGRGeometry*>(pahGeometries[iGeometry]);
// 后期gv_rasterize_one_shape函数可能会变，此处后期需要修改
gv_rasterize_one_shape( static_cast<unsigned char *>(pData), 0, 0,
nBufXSize, nBufYSize,
1, eBufType, bAllTouched, poGeom,
&dfBurnValue, eBurnValueSource,
eMergeAlg,
pfnTransformer, pTransformArg );
if( !pfnProgress((iGeometry+1)/static_cast<double>(nGeomCount),
"", pProgressArg) )
{
CPLError( CE_Failure, CPLE_UserInterrupt, "User terminated" );
eErr = CE_Failure;
}
}
if( bNeedToFreeTransformer )
GDALDestroyTransformer( pTransformArg );
return eErr;
}