[gdal-dev] Interpolation when using the WMS format

[Peter Hopfgartner]

Am 26.09.2014 um 19:22 schrieb Even Rouault <even.rouault at spatialys.com>:

> Peter,
> 
Hi Even,

> This is an interesting proof of concept.
> 
> I have several notes :
> - not sure about your naming conventions. For me your 'top' and 'bottom' must 
> be inverted. In imaging convention, the y of top is < to the y of bottom
> - the formula is only appropriate for a resampling up to a factor of 2
> - you might have edge effects at block border since you clamp to the current 
> block. For example, this could be problematic when operating on blocks with a 
> 1-line height.
> - something ready for upstreaming would probably involve adding a new argument 
> to RasterIO to specify the resampling method, and as you noted, generalizing 
> to other data types.
> - taking into nodata, alpha channel, etc.. would be necessary
> 
> Would probably be interesting to think if we cannot share code with overview 
> computation. But not immediately trivial to do so.
> 
I agree with all of the above points. Most choices were made to keep the change simple.

> Best regards,
> 
> Even
> 
Regards,

Peter

>> 
>> I finally took the time to have a better look at this.
>> 
>> The attached patch is only for our special case, where data arrives in 8
>> bit bands  and is certainly far from being decent (I've written my last
>> C++ code approx. 15 years ago). Anyway, the image quality seems indeed
>> to improve sensibly.
>> 
>> I used the current SVN version as a base for the development.
>> 
>> Applying the patch I get from
>> https://dl.dropboxusercontent.com/u/4935329/resampling_tests/basemap.2000x2
>> 000-quasiorig.jpg to this
>> https://dl.dropboxusercontent.com/u/4935329/resampling_tests/basemap.2000x2
>> 000.bilinear.jpg .
>> 
>> Anyway, the execution time approximatly doubles (on my 2011 notebook it
>> passes from  ~ 1.8 s to ~ 3.4 s), which in our case is not really an
>> issue, but probaly for almost everybody else.
>> 
>> The command line is, starting from the compilation dir:
>> 
>> apps/gdal_translate -srcwin 35555000 23538000 2500 2500 -of JPEG
>> -outsize 2000 2000 basemap.xml basemap.2000x2000.bilinear.jpg .
>> 
>> Any comment is highly appreciated.
>> 
>> Regards and a nice weekend,
>> 
>> Peter
> 
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