3

I'm trying to georeference a geological map of Egypt from 1981, but I don't know which CRS to chose, either the transformation type nor the resampling method...

And once the georeferencing of the map is made, is there any way to convert it to another CRS? For example, WGS 84 or another one more standard?

I'll let you the image of the map where the only information given is that it uses the Lambert Conformal Conic Projection.

enter image description here

2

You've got so many lat-long points to georeference it probably doesnt matter much what you use. I just created eight points at some graticule grid points and warped the raster to EPSG:4326 (lat-long). The results look pretty good.

enter image description here

If what you really wanted to do was assign the correct CRS of the original image to it then you'd have to work out what the standard parallels and the spheroid parameters of the map were, and how real distance scales to pixels. If you're going to warp it to lat-long grids you may as well do as I did and warp it when you reference it.

  • 1
    Since the map is dated 1981, it is most likely not WGS84. It might be Egypt 1907 EPSG:4229, Egypt 1930 or ED50. asprs.org/a/resources/grids/11-2008-egypt.pdf or the EPSG registry have the shift parameters for those. – AndreJ May 23 '16 at 7:41
  • 1
    Searching for "Egypt" in the EPSG registry database was the first thing I did, and none of those are Lambert Conformal Conic projections, so don't help us understand the mapping of geographic coordinates onto the conical projection we see here. One of them may well define the meaning of the lat-long coordinates here, but at this scale I suspect they are sub-pixel differences compared to the gross problem of working out how the cone was constructed and the sphere or spheroid projected onto it. – Spacedman May 23 '16 at 7:46
  • 1
    You might be right on the precision. The central meridian of the projection seems to be 31°E, which is the only meridian straight vertically. The spheroid might well be one of the GCS I mentioned. – AndreJ May 23 '16 at 7:56
  • I tried georeferencing using Egypt 1930 and had very good results. Thanks for your help. – Bastien Sgls May 29 '16 at 9:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.