Qingfeng (Gene) Guan wrote:
I am trying to write a program which is able to create a raster dataset
of any supported format. To do so, I first created a virtual dataset in
memory using the Create() function, then set the projection and add the
bands to the virtual dataset (no links to source datasets), and then
used the CreateCopy() function to create a non-virtual dataset from the
virtual dataset I just created. However, the CreateCopy() always
returned a NULL pointer. I also tried creating a temporary vrt file
using the Create() function before using CreateCopy(). Still, the
CreateCopy() returned a NULL pointer.
Has anyone done this before or have any idea how to do this? Do I have
to link a source dataset to the virtual dataset before using
CreateCopy() to create a non-virtual dataset from the virtual dataset? I
just want to create an empty dataset in which all the pixels are set to
some initial value (for example, zero).
I am using GDAL 1.5.3. <http://1.5.3./> The following is the code I wrote:
...
GDALDriver *poDriver = (GDALDriver *) GDALGetDriverByName( "VRT" );
GDALDataset *poVRTDS;
poVRTDS = poVRTDriver->Create("", xSize, ySize,
3, GDT_Byte,
NULL);
Gene,
It turns out that VRTSourcedRasterBand::IRasterIO() returns CE_Failure if
there are no sources for the band. I believe this is an inappropriate
behavior, and unnecessarily interferes in situations like yours.
I would appreciate your filing a trac ticket on the issue, and I'll look
into applying a fix. Tentatively I'm considering this change
in gdal/frmts/vrt/vrtsourcedrasterband.cpp:
Index: vrtsourcedrasterband.cpp
===================================================================
--- vrtsourcedrasterband.cpp (revision 15924)
+++ vrtsourcedrasterband.cpp (working copy)
@@ -122,7 +122,7 @@
{
int iSource;
- CPLErr eErr = CE_Failure;
+ CPLErr eErr = CE_None;
if( eRWFlag == GF_Write )
{
@@ -171,7 +171,7 @@
/* -------------------------------------------------------------------- */
/* Overlay each source in turn over top this. */
/* -------------------------------------------------------------------- */
- for( iSource = 0; iSource < nSources; iSource++ )
+ for( iSource = 0; eErr == CE_None && iSource < nSources; iSource++ )
{
eErr =
papoSources[iSource]->RasterIO( nXOff, nYOff, nXSize, nYSize,
You might want to try it yourself.
Best regards,
--
---------------------------------------+--------------------------------------
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 Programmer for Rent
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