Pyproj Azimuthal Equidistant (AEQD) transformation always gives a small rotation as compared to country-specific CRS transformations #1362
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I have no idea if this is expected, but... My suggestion is that you should make a https://stackoverflow.com/help/minimal-reproducible-example with real coordinates and show the transformation. You could probably pick a single coordinate that shows the unexpected rotation (like one of the corners of your polygon) when compared with the other transformation. You could also include the center/reference coordinate as one of these example coordinates. Once you have shown that you get the unexpected results in pyproj, convert your example to using |
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I am calculating building polygons from a satellite image.
This works accurately when using a country-specific CRS.
I would like to use a customer CRS, specific to the location at hand, but find that the resulting GPS coordinates are always slightly rotated.
The process I use is:
What I observe is that I get a small rotational difference when using different CRS transformations. Of course, some difference is expected when using different transformations as there is no single way to 'unwrap' the earth to a surface. My assumption is that a country-specific CRS (for a small country such as the Netherlands) should be very similar to using a custom CRS at the exact GPS position (because the datums are very close and the coverage of the country-specific transformation is quite small, in the order of ~400x400km).
After playing with a couple of locations all over the world, it seems that when using the Azimuthal Equidistant (AEQD) transformation, I end up with a small rotation as compared to the country-specific EPSG.
Concretely, I have two examples here from the Netherlands and France.
As you can see from the animated GIFs, the centerpoint of the projection is exactly the same, but there is a minor difference in rotation.
The country-specific EPSGs are most accurate (or at least seem to be).
More details:
Conclusion: after spending a significant amount of time debugging this, I think this might be a bug in the PROJ (or pyproj) library, which could result from a numerical issue. However, I want to rule out that I missed something in the process. Also posted this in the stackexchange geo forum (https://gis.stackexchange.com/questions/470746/pyproj-azimuthal-equidistant-aeqd-transformation-always-gives-a-small-rotation)
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