On Fri, Nov 18, 2016 at 12:44 AM, Rahkonen Jukka (MML) < [email protected]> wrote:
> I do not quite believe that your output pixels are non-square. I rather > think that what you see are views of the native 4326 pixels reprojected > into 3857. In Scotland (7536002 N in epsg:3857) projecting data from 4326 > to 3857 is making quite a big stretch in Nort-South direction. With your > test GetMap request the pixel size in output is about 2.33 millimeters > which must mean heavy oversampling. > > > Thanks for the reply! You are correct: the images I displayed are zoomed pretty far in, resulting in heavy oversampling. Here's a sample showing one pixel (blue highlight) on the heavily oversampled image: http://i.imgur.com/scO8iIm.png It is the oversampling I am trying to understand. Here is a heavily oversampled GetMap with data which went through gdalwarp to reproject the data from 4326 to 3857... then I use Mapserver to display the results setting the input & output PROJECTION blocks to 3857: http://i.imgur.com/MrfDb1E.png I expected Mapserver reproject on the fly to look more like this. Instead, oversampled pixels are stretched, like this: http://i.imgur.com/bw4pNPX.png I played around with various `PROCESSING "RESAMPLE=resample_method"` in my layer, but I get the same stretched output on heavily oversampled output using Mapserver to reproject on the fly from 4326 to 3857. When zoomed out to near-native resolution of my monitor, the output looks great. I only notice the stretching when oversampled. What is Mapserver using to reproject on the fly? Thanks again! Pete
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