[gdal-dev] Problem with gdal1.8 Java bindings gdal.ReprojectImage, produces no data

[William Kang]

Hi Even,
I have tried the method you suggested and it worked! I have similar
result as Ivan tested. For the record, here are two solutions for
handling this problem:

*************************************
1. Using CreateCopy:
SpatialReference dstRef = new SpatialReference("");
dstRef.ImportFromEPSG(26919);

Dataset in_ds = gdal.Open(inPath, gdalconst.GA_ReadOnly);
Dataset vrt_ds = gdal.AutoCreateWarpedVRT(in_ds,
in_ds.GetProjection(), dstRef.ExportToWkt());
Dataset out_ds = in_ds.GetDriver().CreateCopy(outPath, vrt_ds);

clean up..

2. Using ReprojectImage
SpatialReference dstRef = new SpatialReference("");
dstRef.ImportFromEPSG(26919);

Dataset in_ds = gdal.Open(inPath, gdalconst.GA_ReadOnly);
Dataset vrt_ds = gdal.AutoCreateWarpedVRT(in_ds,
in_ds.GetProjection(), dstRef.ExportToWkt());
Dataset out_ds = out_ds = in_ds.GetDriver().Create(outPath,
vrt_ds.getRasterXSize(), vrt_ds.getRasterYSize(),
					in_ds.getRasterCount());

out_ds.SetProjection(vrt_ds.GetProjection());
out_ds.SetGeoTransform(vrt_ds.GetGeoTransform());

if (gdal.ReprojectImage(in_ds, out_ds) == gdalconst.CE_Failure)
		System.out.println("Something in reprojection is wrong");

clean up..
***********************

The speed of the two above solutions are very similar in both cases
for a 5000 x 5000 image. However, the tif image I created by using
creatcopy method is 40k larger than the reprojectimage method.

One problem is that it is way slower than the gdalwarp.exe in windwos
7. Any insights about why the java binding version is so slow? This
makes me think that I probably should run a command line gdalwarp.exe
inside java by using java runtime. Any suggestion?

Thanks a lot.


William

On Sun, May 8, 2011 at 4:44 AM, Even Rouault
<even.rouault at mines-paris.org> wrote:
> William,
>
> Using ReprojectImage() requires some involved preliminary steps. It is
> generally not appropriate to reuse the dimensions of the in_ds for the out_ds,
> because the shape of the reprojected image is generally not the same as the in
> image. But the real error is to reuse the in geotransform as the out
> geotransform. It doesn't make any sense when the in and out projections are
> not the same. Unfortunately there's no easy way of guessing the out
> geotransform.
>
> A simple approximation would be to compute the coordinates of the 4 corners of
> the in image, reproject them to the dstRef and compute from them the out
> geotransform.
>
> What you would need is the GDALSuggestedWarpOutput2() function of
> http://trac.osgeo.org/gdal/browser/trunk/gdal/alg/gdaltransformer.cpp, which
> is used by the gdalwarp utility, but it is not available from Java. It is
> generally called with pfnTransformer = GDALGenImgProjTransform and
> hTransformArg = GDALCreateGenImgProjTransformer2( hSrcDS, NULL, papszOptions )
> for your use case.
>
> But I'm thinking of an easier way. You could use gdal.AutoCreateWarpedVRT()
> that will create a in-memory VRT dataset using the above methods to guess the
> appropriate dimensions and geotransform. Then, you can CreateCopy() into a
> "real" dataset.
>
> See
> http://gdal.org/java/org/gdal/gdal/gdal.html#AutoCreateWarpedVRT(org.gdal.gdal.Dataset,
> %20java.lang.String,%20java.lang.String)
>
> Something like :
>
> Dataset vrt_ds = gdal.AutoCreateWarpedVRT(in_ds, null, dstRef.ExportToWkt());
> Dataset out_ds = gdal.GetDriverByName("GTiff").CreateCopy(outPath, vrt_ds);
> vrt_ds.delete();
> out_ds.delete();
>
> This will be a bit slower than ReprojectImage() but this should work.
>
> Best regards,
>
> Even
>
>
>> Hi folks,
>> I am new to this mailing list. Thanks all for your great job on GDAL/OGR.
>>
>> I have a problem with the gdal.ReprojectImage from gdal1.8 Java
>> bindings. When I perform the reprojection, the projected image is
>> totally black. And the origin of the projected image is wrong too.
>> There were no error popping up at all. The code is as following:
>>
>>               Dataset in_ds = gdal.Open(inPath, gdalconst.GA_ReadOnly);
>>               Dataset out_ds = in_ds.GetDriver().Create(outPath,
>> in_ds.getRasterXSize(), in_ds.getRasterYSize(),
>>                               in_ds.getRasterCount());
>>
>>               try {
>>                       SpatialReference dstRef = new SpatialReference("");
>>                       dstRef.ImportFromEPSG(26919);
>>
>>                       out_ds.SetProjection(dstRef.ExportToWkt());
>>                       out_ds.SetGeoTransform(in_ds.GetGeoTransform());
>>
>>                       if (gdal.ReprojectImage(in_ds, out_ds) == gdalconst.CE_Failure)
>>                               System.out.println("something is wrong");
>>               } finally {
>>                       in_ds.delete();
>>                       out_ds.delete();
>>               }
>>
>> Does anybody know what's going on here? Thanks a lot.
>>
>>
>> William
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>