RasterSymbolizer grid artifacts on reprojections #1035

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Komzpa opened this Issue Jan 17, 2012 · 3 comments

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Komzpa commented Jan 17, 2012

given: mapnik2 old trunk, SRTM geotiff, stylesheets with rastersymbolizer/colorizer, gdal datasource.

if projections aren't exactly the same, (even if their descriptions don't match which is the case when using nik2img standalone or tirex which resets the projection by itself), raster gets a grid of (probably) bad rounding.

screenshot:
http://latlon.org/~komzpa/screenshots/relief-mapnik-broken-reproj.png

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springmeyer commented Jan 17, 2012

Would it be possible to post a reduced test case?

Komzpa commented Jan 18, 2012

Well, sorry for not chopping it down too much, here is the stylesheet on screenshot above:

http://2.osmosnimki.ru/mapnik-ele-simple.xml

to reproduce, you can just drop entries for CleanTopo and planet_osm_line. To generate srtmm.xml, just take a tiff from http://gis-lab.info/data/srtm-tif/,

gdalwarp -s_srs "+proj=longlat" -t_srs "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs +over" -overwrite -r cubicspline sourcetiff.tif resulttiff.tif

after that, do:

gdalbuildvrt srtmm.xml *.tif

to add those to gdal virtual raster.

seems to me you can also get the same result without reprojecting tiffs to mercator but taking them as-is in epsg4326.

springmeyer removed this from the Mapnik 2.1.1 milestone Sep 6, 2014

springmeyer added the post3x label Sep 6, 2014

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springmeyer commented Sep 6, 2014

closing, will address over at #1049

springmeyer closed this Sep 6, 2014

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