[gdal-dev] Slow warping

[Ari Jolma]

I warped an image for which I estimated a geotransform. I'm wondering 
why it took so long (hours).

My source image is a jpeg, lets call it src.jpg. I add the geotransform 
as a jpgw-file.

This goes fast:

gdal_translate -of JPEG src.jpg test.jpg
Input file size is 6048, 4032
0...10...20...30...40...50...60...70...80...90...100 - done.

but the result is not warped, there is a test.jpg-aux.xml file, which 
contains the original geotransform.

gdalwarp does not do it:

gdalwarp -of JPEG jpg-3067/09410_001.jpg test2.jpg
Output driver `JPEG' not recognised or does not support
direct output file creation.

Using the AutoCreateWarpedVRT in bindings works:

use Geo::GDAL;

my $dataset = Geo::GDAL::Open('src.jpg');
my $warped = Geo::GDAL::AutoCreateWarpedVRT($dataset);
Geo::GDAL::Driver('JPEG')->Copy('tets3.jpg', $warped, 1, undef, sub {my 
$prog = shift; say $prog});

but it is really slow.

Does QGIS use AutoCreateWarpedVRT when it does on-the-fly reprojection? 
It outputs

Warning: Creating Warped VRT.

to the terminal. And it is fast.

Ari