I have a raster (JEPG) image from a full planet surface (in this case Jupiter).

I use QGIS and its plugin Georeferencer to add control points on the image. I use the four corners. Then I use Gdal to warp the new georeferenced image into north azimuthal projection. But the final image isn't a circle at all! So I probably missed something during the process.

Here is the full process I followed:

  1. Open the raster in Georeferencer QGIS's plugin
  2. Set the coordinate reference system as WGS84 (EPSG:4326)
  3. Select four points (corners) of the raster and set the destination value:
    1. Select upper left corner and set X/Y to -180/90
    2. Select upper right corner and set X/Y to 180/90
    3. Select lower left corner and set X/Y to -180/-90
    4. Select upper right corner and set X/Y to -180/-90
  4. Configure the transformation setting to the following parameters:
    • Transformation Type: Polynomial 1
    • Resampling method: cubic
    • Compression: None
  5. Georeference image.
  6. Warp into azimuthal projectino with gdarwarp : gdalwarp -t_srs "+proj=aeqd +lat_0=90 +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs" jupiter_georef.tif jupiter_circle.tiff

Unfortunately, the final image doesn't match a full circle.

The georeferencer screen : Georefrencer screen

Output: Output

I also tried to use QGIS to warp the georeferenced image by changing the coordinate system. The output is better but the circle is cropped by a square and it has a thin line missing. enter image description here

Any clue to solve this problem?

  • You might need to use the correct Spatial Reference.You might want Jupiter 2000 spatialreference.org/ref/iau2000/59901 – Mapperz Sep 30 '20 at 15:46
  • I don't think the problem comes from the Jupiter spatial reference or Earth one. As the raster image could be any planet surface and in first approximation it's a sphere, it must works for any kind of rectangular images. – Elendil Oct 1 '20 at 16:10

Finally I managed to make a simple polar projection without georeferencing the raster image. For that I used ImageMagick with the following command line:

convert raster_input.jpg -virtual-pixel HorizontalTile -background Black -distort Polar 0 -fuzz 50% -trim polar_output.jpg

I know there is another solution with Gimp through the Filters > Distort > Polar Coordinates tool. But I chose the ImageMagick approach as I have several image to treat and its easiest to script it.

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