[gdal-dev] Availability of Lanczos and cubicspline in gdaladdo

[Frank Warmerdam]

Benoit Andrieu wrote:
> Thanks for the answer Frank !
> 
> So in a first time I'll be looking at making a gdaladdo bis.
> 
> By the way, do you know why Mapserver does "only" support nearest, average, bilinear, bicubic ?
> I thought it was using GDAL to do warping, but then it would natively support cubicspline and lanczos.
> I know that speed is a concern... ^^

Benoit,

MapServer has it's own resampling code focused more on speed than precision (or
featurefulness).  It does not actually have any cubic support as far as I know.
I had intended to implement this but never got to it.

> By the way bis, I forgot to mention that we had some artifacts with gdalwarp yesterday.
> We are using FWTools 2.3.1.
> We wanted to merge several pictures at 20cm x 20cm resolution and make a 1m x 1m and a 4m x 4m.
> The pictures could be quite big : 30000 x 30000 pixels.
> 
> First, we used gdalwarp to do all operations in a single one : merging and downsizing.
> But the resulting picture contained artifacts. In some areas, it is as if a nearest method was used instead of lanczos.
> 
> Because of this, we then asked gdalwarp to make the downsizing. In a second call, we made the merging.
> There we did not find artifacts and it is ok for us to do like this.
> But I fear to have the same problems with bigger pictures.
> 
> I will not be able to provide the pictures (sources or results) because of confidentiality agreements.
> But I could provide screenshots.
> Or try to reproduce on differents datasets.

I would encourage you to produce test images that demonstrate the
artifacts clearly and that are submitable.  Before submitting a bug report
it would be good to confirm the problem with the latest "trunk" code.

Best regards,
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