Thank you, Even. For now I'll proceed with the additional warping. Just for my education: are square pixels a requirement for EPSG:3857?
On Thu, Feb 5, 2015 at 11:50 AM, Even Rouault <even.roua...@spatialys.com> wrote: > Le jeudi 05 février 2015 17:41:22, Jesse McGraw a écrit : > > Thanks Even. > > > > I did try re-warping the cropped output to 3857 again and it does produce > > square pixels but at the expense of an additional warping operation > > > > I'm just curious why the warping that is part of the -crop_to_cutline > > process is changing the pixel ratio while a regular, non-cropping warping > > makes them square > > I think I explained it in my previous answer. This is because > -crop_to_cutline > uses -te internally, which in the general case doesn't allow pixel squares. > And non-cropping warping doesn't necessarily preserve extent of the output > to > be the same as extent of the input (even in non-reprojection cases). You > can > check that actually by comparing gdalinfo on the temporary and final > datasets. > There's no fundamental reason why -crop_to_cutline couldn't produce exact > square pixels, if people are annoyed by that behaviour. Just someone has > to do > it... > > > > > On Thu, Feb 5, 2015 at 11:36 AM, Even Rouault < > even.roua...@spatialys.com> > > > > wrote: > > > Le jeudi 05 février 2015 17:23:06, Jesse McGraw a écrit : > > > > I'm not sure whether this is a real issue or not but I thought I'd > > > > bring > > > > > > it > > > > > > > up, at the very least I'll learn something > > > > > > > > When using "gdalwarp -cutline <shapefile> -crop_to_cutline" on an > input > > > > raster that is in EPSG:3857 with square-pixels the output raster, > while > > > > still EPSG:3857, now has non-square pixels. > > > > > > > > They're aren't terribly non-square but aren't they supposed to be > > > > completely square for EPSG:3857? > > > > > > Perhaps... Actually the effet of -crop_to_cutline is exactly the same > as > > > manually passing the target extents with -te with the bounding box of > the > > > cutline. > > > It is not possible to both preserve the extent extents and pixel size > at > > > the > > > same time, due to width and height being integer values. > > > So, in order to preserve pixel square, the extent should be modified a > > > little > > > bit. What is more appropriate is a matter of point of view I think. > > > You can always re-run "gdalwarp tmp.tif out.tif" where tmp.tif is the > > > output > > > of first gdalwarp with -crop_to_cutline. And you should get square > pixels > > > I believe. > > > > > > > (FWIW, I see that there are tickets opened that reference similar > > > > issues but they reference the output being shifted or the origin > > > > changing, not > > > > > > the > > > > > > > pixel shape changing) > > > > > > > > For example: > > > > #Warp our original .tif to EPSG:3857 > > > > $gdalwarp \ > > > > > > > > -t_srs EPSG:3857 \ > > > > -dstalpha \ > > > > -co TILED=YES \ > > > > "ENR_L33.tif" \ > > > > "./2.tif" > > > > > > > > #See that the output pixels are square > > > > $gdalinfo 2.tif > > > > Origin = (-8577554.996301921084523,5421778.172851986251771) > > > > Pixel Size = (43.677179501975118,-43.677179501975118) > > > > > > > > > > > > #Now crop the image to a cutline > > > > $gdalwarp \ > > > > > > > > -crop_to_cutline \ > > > > -dstalpha \ > > > > -cutline "./ENR_L33.shp" \ > > > > -cblend 10 \ > > > > -co TILED=YES \ > > > > "./2.tif" \ > > > > "./3.tif" > > > > > > > > #See that output pixels are not square > > > > $ gdalinfo 3.tif > > > > Origin = (-8480047.445924906060100,5366376.137789577245712) > > > > Pixel Size = (43.678439570399853,-43.675457269061347) > > > > > > > > > > > > I ran some more tests and without the -crop_to_cutline option the > > > > output pixels remain square > > > > > > > > Thanks, > > > > > > > > Jesse > > > > > > -- > > > Spatialys - Geospatial professional services > > > http://www.spatialys.com > > -- > Spatialys - Geospatial professional services > http://www.spatialys.com >
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