Thanks Frank.
So I think I need to do something like the code below instead, ie, create a
"MEM" dataset and later create-copy to a "PNG" dataset. This seems to be
working (although the content of the image is all wrong - but that's another
issue for me to try to figure out).
Thanks again,
Nik.
GDALDatasetH memDS = GDALCreate( GDALGetDriverByName("MEM"), "tmp", 256, 256,
4, GDT_Float32, NULL );
…
…
…
char **options = NULL;
options = CSLSetNameValue( papszOptions, "WORLDFILE", "NO" );
options = CSLSetNameValue( papszOptions, "ZLEVEL", "9" );
GDALDatasetH dstDS = GDALCreate( hDriver, "/var/tmp/image.png", 256, 256, 4,
GDT_Float32, options );
GDALDatasetH dstDS = GDALCreateCopy( GDALGetDriverByName("PNG"),
"/var/tmp/image.png", memDS, FALSE, options, NULL, NULL );
On 17/07/2013, at 4:50 PM, Frank Warmerdam <[email protected]> wrote:
> Nik,
>
> No, the PNG format does not support direct creation, only creation by copying
> an existing dataset (GDALCreateCopy()). You can interactively see the
> capabilities of a driver like this:
>
> gdalinfo --format png
> Format Details:
> Short Name: PNG
> Long Name: Portable Network Graphics
> Extension: png
> Mime Type: image/png
> Help Topic: frmt_various.html#PNG
> Supports: CreateCopy() - Create dataset by copying another.
> Supports: Virtual IO - eg. /vsimem/
> Creation Datatypes: Byte UInt16
>
> <CreationOptionList>
> <Option name="WORLDFILE" type="boolean" description="Create world file" />
> <Option name="ZLEVEL" type="int" description="DEFLATE compression level
> 1-9" default="6" />
> </CreationOptionList>
>
> The "Supports: CreateCopy()" means you can create the format, but only by
> copying an existing dataset. Formats supporting creation will have
> "Supports: Create()". You can get a broad listing of all formats like this:
>
> gdalinfo --formats
> ....
> SDTS (rov): SDTS Raster
> DTED (rwv): DTED Elevation Raster
> PNG (rwv): Portable Network Graphics
> JPEG (rwv): JPEG JFIF
> MEM (rw+): In Memory Raster
> ...
>
> The "w" means it supports at least CreateCopy(). The "+" means it supports
> create+update.
>
> Best regards,
>
>
>
> On Tue, Jul 16, 2013 at 10:14 PM, Nik Sands <[email protected]> wrote:
> Can I use GDALCreate to create (and later write to) PNG images?
> If so, is "PNG" the correct string for GDALGetDriverByName?
>
> Otherwise, can somebody please let me know why the code below returns NULL
> from GDALCreate (assigned to dstDS)?
>
> Advice much appreciated, as always.
>
> Thanks,
> Nik.
>
>
>
> GDALDriverH hDriver = GDALGetDriverByName("PNG");
> char **papszOptions = NULL;
>
> papszOptions = CSLSetNameValue( papszOptions, "WORLDFILE", "NO" );
> papszOptions = CSLSetNameValue( papszOptions, "ZLEVEL", "9" );
>
> GDALDatasetH dstDS = GDALCreate( hDriver, "/var/tmp/image.png", 256,
> 256, 4, GDT_Float32, papszOptions );
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> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
>
>
> --
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up | Frank Warmerdam, [email protected]
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush | Geospatial Software Developer
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