[gdal-dev] gdal warp with approximate transformation seems a bit slow...

[G. Allegri]

2011/6/1 Chaitanya kumar CH <chaitanya.ch at gmail.com>

> Giovanni,
>
> You can use the -et option of gdalwarp. [1]


> Are you sure qgis is warping the whole image and not just the scaled down
> version of the original? Processing a half giga pixel image ought to be
> longer than instantaneous.
>

Probably you're right... I will investigate more. Thanks for the hint.


>
> [1]: http://www.gdal.org/gdalwarp.html
>
> On Wed, Jun 1, 2011 at 9:55 PM, G. Allegri <giohappy at gmail.com> wrote:
>
>> I was doing some tests on Gvsig for raster reprojection, where gdal warp
>> is used. Gvsig uses a default error threshold of 0.125, which AFAIK makes
>> gdal warp fall back to an approximate transformation. Anyway the
>> reprojection is quite slow, even if significantly faster then
>> GDALGenImgProjTransform.
>>
>> My test is against a 21698P x 24647L ArcInfo Binary Grid, with a single
>> band with block dimensions 256x4. Bot SRSs are projected.
>> The command is: > gdalwarp -s_srs EPSG:3003 -t_srs EPSG:23032 -et 0.125
>> hdr.adf test.tiff
>> It took about 9 minutes to complete.
>>
>> Loading the same raster on QGis, which implements its own approximate
>> transformation for on-the-fly reprojection [1], is istantaneous.
>> I was wondering if a similar algorithm could be use within Gdal...
>>
>> Giovanni
>>
>> [1]
>> http://trac.osgeo.org/qgis/browser/trunk/qgis/src/core/qgsrasterprojector.cpp
>>
>>
>>
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>>
>
>
>
> --
> Best regards,
> Chaitanya kumar CH.
> /tʃaɪθənjə/ /kʊmɑr/
> +91-9494447584
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>
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