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RFC 59.1 : GDAL/OGR utilities as a library
Authors: Faza Mahamood, Even Rouault
Contact: fazamhd at gmail dot com, even.rouault at spatialys.com
Status: Development
Implementation version: 2.1
Summary
This RFC defines how to expose GDAL/OGR C/C++ utilities as C callable functions. The utility code is modified to call the new function. This RFC gives a general frame and principles, demonstrated with gdalinfo and gdal_translate, but aimed at being extended with other utilities.
Rationale
There is a need for calling GDAL utilities from code without involving system calls, to be able to work on in-memory datasets and use progress/cancellation callback functions.
Changes
A public header file gdal_utils.h is created which contains the public declarations of GDAL utilities. The current header(still in progress) can be found here.
Each utility has a function (XXXXOptionsNew) to create an option structure from arguments specified as an array of strings. This function also accepts as argument an extra semi-private structure used to cooperate with the code of the command line utility itself.
For GDALInfo():
/*! Options for GDALInfo(). Opaque type */ typedef struct GDALInfoOptions GDALInfoOptions; typedef struct GDALInfoOptionsForBinary GDALInfoOptionsForBinary; /** * Allocates a GDALInfoOptions struct. * * @param papszArgv NULL terminated list of options (potentially including filename and open options too) * The accepted options are the one of the gdalinfo utility. * @param psOptionsForBinary (output) may be NULL (and should generally be NULL), * otherwise (gdalinfo_bin.cpp use case) must be allocated with * GDALInfoOptionsForBinaryNew() prior to this function. Will be * filled with potentially present filename, open options, subdataset number... * @return pointer to the allocated GDALInfoOptions struct. * * @since GDAL 2.1 */ GDALInfoOptions CPL_DLL *GDALInfoOptionsNew(char** papszArgv, GDALInfoOptionsForBinary* psOptionsForBinary); void CPL_DLL GDALInfoOptionsFree( GDALInfoOptions *psOptions ); /** * Lists various information about a GDAL supported raster dataset. * * GDALInfoOptions* must be allocated and freed with GDALInfoOptionsNew() * and GDALInfoOptionsFree() respectively. * * @param hDataset the dataset handle. * @param psOptions the options structure returned by GDALInfoOptionsNew() or NULL. * @return string corresponding to the information about the raster dataset. * It must be freed using CPLFree(). * * @since GDAL 2.1 */ char CPL_DLL *GDALInfo( GDALDatasetH hDataset, const GDALInfoOptions *psOptions );
Similarly for GDALTranslate():
/*! Options for GDALTranslate(). Opaque type */
typedef struct GDALTranslateOptions GDALTranslateOptions;
typedef struct GDALTranslateOptionsForBinary GDALTranslateOptionsForBinary;
GDALTranslateOptions CPL_DLL *GDALTranslateOptionsNew(char** papszArgv,
GDALTranslateOptionsForBinary* psOptionsForBinary);
void CPL_DLL GDALTranslateOptionsFree( GDALTranslateOptions *psOptions );
void CPL_DLL GDALTranslateOptionsSetProgress( GDALTranslateOptions *psOptions,
GDALProgressFunc pfnProgress,
void *pProgressData );
GDALDatasetH CPL_DLL GDALTranslate(const char *pszDestFilename,
GDALDatasetH hSrcDataset,
const GDALTranslateOptions *psOptions,
int *pbUsageError);
SWIG bindings (Python / Java / C# / Perl) changes
For all bindings, the above functions are mapped to SWIG with :
struct GDALInfoOptions {
%extend {
GDALInfoOptions(char** options) {
return GDALInfoOptionsNew(options, NULL);
}
~GDALInfoOptions() {
GDALInfoOptionsFree( self );
}
}
};
%rename (InfoInternal) GDALInfo;
char *GDALInfo( GDALDatasetShadow *hDataset, GDALInfoOptions *infoOptions );
struct GDALTranslateOptions {
%extend {
GDALTranslateOptions(char** options) {
return GDALTranslateOptionsNew(options, NULL);
}
~GDALTranslateOptions() {
GDALTranslateOptionsFree( self );
}
}
};
%rename (TranslateInternal) wrapper_GDALTranslate;
%newobject wrapper_GDALTranslate;
%inline %{
GDALDatasetShadow* wrapper_GDALTranslate( const char* dest,
GDALDatasetShadow* dataset,
GDALTranslateOptions* translateOptions,
GDALProgressFunc callback=NULL,
void* callback_data=NULL)
{
int usageError; /* ignored */
GDALTranslateOptionsSetProgress(translateOptions, callback, callback_data);
return GDALTranslate(dest, dataset, translateOptions, &usageError);
}
For Python bindings, convenience wrappers are created to allow specifying options in a more user friendly way.
def InfoOptions(options = [], format = 'text', deserialize = True,
computeMinMax = False, reportHistograms = False, reportProj4 = False,
stats = False, approxStats = False, computeChecksum = False,
showGCPs = True, showMetadata = True, showRAT = True, showColorTable = True,
listMDD = False, showFileList = True, allMetadata = False,
extraMDDomains = None):
""" Create a InfoOptions() object that can be passed to gdal.Info()
options can be be an array of strings, a string or let empty and filled from other keywords."""
def Info(ds, **kwargs):
""" Return information on a dataset.
Arguments are :
ds --- a Dataset object or a filename
Keyword arguments are :
options --- return of gdal.InfoOptions(), string or array of strings
other keywords arguments of gdal.InfoOptions()
If options is provided as a gdal.InfoOptions() object, other keywords are ignored. """
def TranslateOptions(options = [], format = 'GTiff',
outputType = GDT_Unknown, bandList = None, maskBand = None,
oXSizePixel = 0, oYSizePixel = 0, oXSizePct = 0.0, oYSizePct = 0.0,
xRes = 0.0, yRes = 0.0,
creationOptions = None, srcWin = None, projWin = None, projWinSRS = None, strict = False,
unscale = False, scaleParams = None, exponents = None,
assignedULLR = None, metadataOptions = None,
outputSRS = None, GCPs = None,
noData = None, rgbExpand = None,
stats = False, rat = True, resampling = None,
callback = None, callback_data = None):
""" Create a TranslateOptions() object that can be passed to gdal.Translate()
Keyword arguments are :
options --- can be be an array of strings, a string or let empty and filled from other keywords.
format --- output format ("GTiff", etc...)
outputType --- output type (gdal.GDT_Byte, etc...)
bandList --- array of band numbers (index start at 1)
maskBand --- mask band to generate or not ("none", "auto", "mask", 1, ...)
oXSizePixel --- width of the output raster in pixel
oYSizePixel --- height of the output raster in pixel
oXSizePct --- width of the output raster in percentage (100 = original size)
oYSizePct --- height of the output raster in percentage (100 = original size)
xRes --- output horizontal resolution
yRes --- output vertical resolution
creationOptions --- list of creation options
srcWin --- subwindow in pixels to extract: [left_x, top_y, width, height]
projWin --- subwindow in projected coordinates to extract: [ulx, uly, lrx, lry]
projWinSRS --- SRS in which projWin is expressed
strict --- strict mode
unscale --- unscale values with scale and offset metadata
scaleParams --- list of scale parameters, each of the form [src_min,src_max] or [src_min,src_max,dst_min,dst_max]
exponents --- list of exponentation parameters
assignedULLR --- assigned output bounds: [ulx, uly, lrx, lry]
metadataOptions --- list of metadata options
outputSRS --- assigned output SRS
GCPs --- list of GCPs
noData --- nodata value (or "none" to unset it)
rgbExpand --- Color palette expansion mode: "gray", "rgb", "rgba"
stats --- whether to calcule statistics
rat --- whether to write source RAT
resampling --- resampling mode
callback --- callback method
callback_data --- user data for callback
"""
def Translate(destName, srcDS, **kwargs):
""" Convert a dataset.
Arguments are :
destName --- Output dataset name
srcDS --- a Dataset object or a filename
Keyword arguments are :
options --- return of gdal.InfoOptions(), string or array of strings
other keywords arguments of gdal.TranslateOptions()
If options is provided as a gdal.TranslateOptions() object, other keywords are ignored. """
gdal.Info() can be used either with setting the attributes of gdal.InfoOptions() or inlined arguments of gdal.Info(). Arguments can be specified as array of strings, command line syntax or dedeicated keywords. So various combinations are possible :
options = gdal.InfoOptions(format = 'json', computeChecksum = True)
gdal.Info(ds, options)
options = gdal.InfoOptions(options = ['-json', '-checksum'])
gdal.Info(ds, options)
options = gdal.InfoOptions(options = '-json -checksum')
gdal.Info(ds, options)
gdal.Info(ds, format = 'json', computeChecksum = True)
gdal.Info(ds, options = ['-json', '-checksum'])
gdal.Info(ds, options = '-json -checksum')
Same for gdal.Translate()
Utilities
Utilities are modified to call the respective function.
Documentation
All new methods/functions are documented.
Test Suite
gdal.Info method is tested in test_gdalinfo_lib.py. gdal.Translate method is tested in test_gdal_translate_lib.py.
Compatibility Issues
None expected. Command line utilities will keep the same interface. It will be checked by ensuring their tests in autotest/utilities still pass.
Open question
What name should be given for librarified ogr2ogr? OGR2OGR() or OGRTranslate() ?
The order of arguments in GDALTranslate(), GDALWarp() and OGR2OGR() is currently dest then source(s).
GDALDatasetH CPL_DLL GDALTranslate(const char *pszDest, GDALDatasetH hSrcDataset, GDALTranslateOptions *psOptions, int *pbUsageError)
GDALDatasetH CPL_DLL GDALWarp( const char *pszDest, GDALDatasetH hDstDS, int nSrcCount,
GDALDatasetH *pahSrcDS, GDALWarpAppOptions *psOptions, int *pbUsageError )
GDALDatasetH CPL_DLL OGR2OGR( const char *pszDest, GDALDatasetH hDstDS, GDALDatasetH hSrcDS,
OGR2OGROptions *psOptions, int *pbUsageError )
It is similar to GDALCreateCopy(const char* pszDestFilename, GDALDatasetH hSrcDS, ....), so at least there's a form of consistency at the API level. Any comments?
Related ticket
Implementation
Implementation will be done by Faza Mahamood and Even Rouault
The proposed implementation lies in the "rfc59.1" branch of the https://github.com/rouault/gdal2/tree/rfc59.1.
The list of changes : https://github.com/rouault/gdal2/compare/rfc59.1
