Am 31.10.2016 um 12:03 schrieb Tom Chadwin:
Someone using qgis2web has experienced the following error:

QgsCsException: forward transform of
(-18933215.197392, -9254444.351822)
PROJ.4: +proj=moll +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
+ellps=WGS84 +towgs84=0,0,0 +to +proj=longlat +datum=WGS84 +no_defs
+ellps=WGS84 +towgs84=0,0,0
Error: acos/asin: |arg| >1.+1e-14

What causes the error? The QGIS project is in EPSG:54009, and either export
to 3857 or to 54009 gives the error above.

The reason lies in the oddity of the Mollweide projection. At full size, large parts of the image can be reprojected to a point on the Earth. Using gdalwarp, this command line will work:

gdalwarp -overwrite -s_srs EPSG:53009 -t_srs EPSG:3857 infile outfile -wo SOURCE_EXTRA=1000

But with On-The-fly-reprojections you can not enter the SOURCE_EXTRA.

If you need a full Earth view, you have to stick to EPSG:4326 or 3857.

BTW Sphere Mollweide EPSG:53009 works far better than World Mollweide EPSG:54009 when it comes to reprojections.

André Joost

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