[gdal-dev] Boundary Artifact with ChunkAndWarpImage

[Matt Hanson]

Mike,
Are you setting padfDstNoDataReal as well?     Because GDAL performs the
warp in chunks I'm wondering if previously written data, that should be
NoData, is not recognized as such with later chunks.   However, I'm still
not clear on the exact details of how that works internally, Even would
have a better idea if this even makes sense.

The code I'm using to set WarpOptions for doing warping on multiple input
images to a single outout looks like the below.   Also, are you setting
INIT_DEST option to "NODATA" (it's one of the key-value options that are
assigned to psWarpOptions->papszWarpOptions).

Hope this helps!

GDALWarpOptions *psWarpOptions = GDALCreateWarpOptions();
psWarpOptions->hDstDS = imgout.GetGDALDataset(); psWarpOptions->nBandCount
= imgout.NumBands(); psWarpOptions->panSrcBands = (int *) CPLMalloc(sizeof(
int) * psWarpOptions->nBandCount ); psWarpOptions->panDstBands = (int *)
CPLMalloc(sizeof(int) * psWarpOptions->nBandCount );
psWarpOptions->padfSrcNoDataReal = (double *) CPLMalloc(sizeof(double) *
psWarpOptions->nBandCount ); psWarpOptions->padfSrcNoDataImag = (double *)
CPLMalloc(sizeof(double) * psWarpOptions->nBandCount );
psWarpOptions->padfDstNoDataReal = (double *) CPLMalloc(sizeof(double) *
psWarpOptions->nBandCount ); psWarpOptions->padfDstNoDataImag = (double *)
CPLMalloc(sizeof(double) * psWarpOptions->nBandCount ); for (unsigned int b=
0;b<imgout.NumBands();b++) { psWarpOptions->panSrcBands[b] = b+1;
psWarpOptions->panDstBands[b] = b+1; psWarpOptions->padfSrcNoDataReal[b] =
images[0][b].NoDataValue(); psWarpOptions->padfDstNoDataReal[b] = imgout[b].
NoDataValue(); psWarpOptions->padfSrcNoDataImag[b] = 0.0;
psWarpOptions->padfDstNoDataImag[b] = 0.0; }

On Thu, Apr 16, 2015 at 1:42 PM, Michael Aschenbeck <
m.g.aschenbeck at gmail.com> wrote:

> Thanks for your reply.
>
> I'm using gdal 1.10.1.  I'm using cubic resampling, but i have noticed the
> dark line artifact with bilinear as well.  I unfortunately do not reproduce
> the problem with a basic gdalwarp with cubic resampling.
>
> I have written this code to do some registration. It's hard to tell in the
> example, but my transformation actually pushed pixels up a bit. The
> transformation I use handles interior pixels nicely and extends beyond the
> image, so there is nothing 'weird' going on with that near the boundary
> that I can think of.
>
> I was hoping there is a warp option i have not yet thought of.
>
> Thanks again,
> Mike
>
>
>
> On Thu, Apr 16, 2015 at 11:10 AM, Even Rouault <even.rouault at spatialys.com
> > wrote:
>
>> Le jeudi 16 avril 2015 19:01:57, Michael Aschenbeck a écrit :
>> > Hello,
>> >
>> > I'm using ChunkAndWarpMulti to warp an image.  The warping is working
>> > nicely, however, at the boundary I seem to be getting some artifacts.
>> >
>> > The first artifact i see is a DARK boundary of pixels in some
>> location.  My
>> > guess is that the interpolator is interpolating with blackfill
>> (intensity
>> > zero pixels).  Note that I am using the following setup:
>> > psWarpOptions->padfSrcNoDataReal = (double *)
>> > CPLMalloc(psWarpOptions->nBandCount*sizeof(double));
>> > for (int ii = 0; ii < psWarpOptions->nBandCount; ii++)
>> > {
>> > psWarpOptions->padfSrcNoDataReal[ii] = 0;
>> > }
>> > which i thought was supposed to treat zeros as nodata.  It doesn't seem
>> to
>> > be doing what I think it should.
>> >
>> > In some cases, I am also noticing a BRIGHT band strip of pixels
>> adjacent to
>> > the dark boundary pixels.  I don't have any thoughts on where this
>> artifact
>> > is coming from.
>> >
>> > Below you can find links to an example.  The orange you see is just the
>> > background color of my viewer.  Zero pixels are set to transparent so
>> you
>> > can see the dark boundary artifact.  (Note that all of the orange
>> region is
>> > covered with zero-intensity pixels, so we haven't reached the boundary
>> of
>> > the file, just the boundary of the non-zero pixels.)  Sorry if that's
>> > confusing.
>> > The before image:
>> https://www.dropbox.com/s/3kmyi8wu0qybsq9/before.JPG?dl=0
>> > The after image with the artifacts:
>> > https://www.dropbox.com/s/fo0m8q95b26s61m/after.JPG?dl=0
>> >
>>
>> Mike,
>>
>> Which gdal version ? Which resampling method ?
>> Do you reproduce with gdalwarp ?
>> If so, providing input file + full gdalwarp command line would help.
>>
>> Even
>>
>> --
>> Spatialys - Geospatial professional services
>> http://www.spatialys.com
>>
>
>
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