[gdal-dev] Looking for a "surefire" way to get valid output formats.

[Even Rouault]

On mardi 16 mai 2017 11:39:03 CEST Vlad wrote:
> Basically trying to keep users from selecting an invalid -of parameter in
> translate and warp.
> 
> Looking at gdalinfo --formats I see this for PNG..
> 
>  PNG -raster- (rwv): Portable Network Graphics
> 
> and gdalinfo --format png, I get...
> 
>  Supports: Open() - Open existing dataset.
>  Supports: CreateCopy() - Create dataset by copying another.
>  Supports: Virtual IO - eg. /vsimem/
> 
> HOWEVER, the key/value pairs in the PNG driver metadata map give me...
> "DCAP_CREATECOPY"=YES
> 
> and no "DCAP_CREATE".
> 
> For a BMP I get a "DCAP_CREATE" = YES, and there is no "DCAP_CREATECOPY",
> however I know translate will work with -of png or -of bmp.
> 
> What should I be looking at to see if a driver short name is a supported
> output type?

I've just improved the doc regarding those aspects. 

Extract:


/** Capability set by a driver that implements the Create() API.
 * 
 * If GDAL_DCAP_CREATE is set, but GDAL_DCAP_CREATECOPY not, a generic
 * CreateCopy() implementation is available and will use the Create() API of
 * the driver.
 * So to test if some CreateCopy() implementation is available, generic or
 * specialize, test for both GDAL_DCAP_CREATE and GDAL_DCAP_CREATECOPY.
 */
#define GDAL_DCAP_CREATE     "DCAP_CREATE"

/** Capability set by a driver that implements the CreateCopy() API. 
 * 
 * If GDAL_DCAP_CREATECOPY is not defined, but GDAL_DCAP_CREATE is set, a generic
 * CreateCopy() implementation is available and will use the Create() API of
 * the driver.
 * So to test if some CreateCopy() implementation is available, generic or
 * specialize, test for both GDAL_DCAP_CREATE and GDAL_DCAP_CREATECOPY.
 */
#define GDAL_DCAP_CREATECOPY "DCAP_CREATECOPY"


/**
 * \brief Create a copy of a dataset.
 *
 * This method will attempt to create a copy of a raster dataset with the
 * indicated filename, and in this drivers format.  Band number, size,
 * type, projection, geotransform and so forth are all to be copied from
 * the provided template dataset.
 *
 * Note that many sequential write once formats (such as JPEG and PNG) don't
 * implement the Create() method but do implement this CreateCopy() method.
 * If the driver doesn't implement CreateCopy(), but does implement Create()
 * then the default CreateCopy() mechanism built on calling Create() will
 * be used.
 * So to test if CreateCopy() is available, you can test if GDAL_DCAP_CREATECOPY
 * or GDAL_DCAP_CREATE is set in the GDAL metadata.
 *
 * It is intended that CreateCopy() will often be used with a source dataset
 * which is a virtual dataset allowing configuration of band types, and other
 * information without actually duplicating raster data (see the VRT driver).
 * This is what is done by the gdal_translate utility for example.
 *
 * That function will try to validate the creation option list passed to the
 * driver with the GDALValidateCreationOptions() method. This check can be
 * disabled by defining the configuration option
 * GDAL_VALIDATE_CREATION_OPTIONS=NO.
 *
 * After you have finished working with the returned dataset, it is
 * <b>required</b> to close it with GDALClose(). This does not only close the
 * file handle, but also ensures that all the data and metadata has been written
 * to the dataset (GDALFlushCache() is not sufficient for that purpose).
 *
 * In some situations, the new dataset can be created in another process through
 * the \ref gdal_api_proxy mechanism.
 *
 * @param pszFilename the name for the new dataset.  UTF-8 encoded.
 * @param poSrcDS the dataset being duplicated.
 * @param bStrict TRUE if the copy must be strictly equivalent, or more
 * normally FALSE indicating that the copy may adapt as needed for the
 * output format.
 * @param papszOptions additional format dependent options controlling
 * creation of the output file. The APPEND_SUBDATASET=YES option can be
 * specified to avoid prior destruction of existing dataset.
 * @param pfnProgress a function to be used to report progress of the copy.
 * @param pProgressData application data passed into progress function.
 *
 * @return a pointer to the newly created dataset (may be read-only access).
 */

GDALDataset *GDALDriver::CreateCopy( const char * pszFilename,
                                     GDALDataset * poSrcDS,
                                     int bStrict, char ** papszOptions,
                                     GDALProgressFunc pfnProgress,
                                     void * pProgressData );

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