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pythondictionarygoogle-mapsmap-projections

Changing image projection using Python

Image corner coordinates are known:

  • Top left: (70.20315, 20.92749)
  • Top right: (70.20315, 31.45240)
  • Bottom left: (59.70571, 20.92749)
  • Bottom right: (59.70571, 31.45240)

(Basically map over Finland and a little bit of Sweden/Norway/Russia)

I couldn't find a way to change image projection to Google maps overlay image, preferably using Python.

It's possible to do that with pyproj and PIL, but I wasn't able to figure out how to do that. I also found GDAL, and more specifically gdalwarp, but couldn't find options for changing projection in a correct way.

Example image

Solution

  • (Copy-paste from gis answer)

    Extensive trial-and-error showed it worked fine without specifying source projection. Same can be achieved using only GDAL Python API. Steps to reproduce:

    Adding control points to TIF (of course, first convert mapimage.png mapimage.tif):

    gdal_translate mapimage.tif mapimage_georeffed.tif -gcp 2300 2300 31.45240 59.70571 -gcp 0 0 20.92749 70.20315 -gcp 2300 0 31.45240 70.20315 -gcp 0 2300 20.92749 59.70571 -a_srs +proj=longlat

    Then, GDAL python bindings include gdal2tiles.py, which autogenerates tiles on right projection for maps, and also sample map pages.

    For the record, I'm not absolutely positive projection is exactly correct, but over that area it seems to be at least good enough.