I stopped following this tutorial because the longtitude lines go towards the poles and the distance in meters decreases.
I have pointed that out here, but it seems that this error is still being made.
This error exists no matter how you go about generating the scenery and cannot be corrected. The reason for this is that, as you point out, the globe cannot be defined as a square grid.
However, Condor requires that you define your scenery as a square grid. In lower latitudes, this is not as apparent as at higher latitudes. In addition, using 3DEM, as the manual instructs, and saving as a Terrain Matrix yields a format that is WGS84, also known as EPSG:4326. This WGS84/EPSG:4326 projection is what is required for imagery tile output for Condor. The disadvantage of WGS84/EPSG:4326 is the distortion at the poles.
In the diagram below, you see a UTM grid in lat/lon on the left. The Condor scenery grid is on the right and it is represented only by pixels. What the calibration file does is provide a direct mapping of pixels to lat/lon. Note that it is a BACKWARDS mapping of pixels with the orgin (0,0) being in the lower right and increasing as you go to the LEFT. Note the line 0,0,-40.56582186,-66.18171986 tells Condor that the lower left corner (the orgin) is at -40.5, -66.1 lat/lon. Likewise, the upper left is 230400,322560,-37.6936068,-68.90715888. That is pixels 230400 and 322560 of the SRTM grid. The calibration points file provides a grid of these lat/lon and pixel locations to Condor and I presume it interpolates between them.
You can see from this that Condor does not know anything about lat/lon at all. It only knows pixels, which are square. This means no matter how you calibrate that there is distortion in the imagery and terrain. However, it is spread over a very large space and isn't really noticeable.
UTM uses varying references in an attempt to more closely match the shape of a globe, thus the necessity for different zones. This makes it impossible build a Condor scenery that spans a UTM zone. Using WGS84/EPSG:4326, there is no zone issue.
Maybe this is not the accurate procedure to obtain an scenery.
I'm still not sure how to discover the issue. Did you follow the whole tutorial and then find the distance error? Even with inaccurate calibration points, if you have lat/lon for your airport and your wp it seems like Condor should calculate the distance properly.
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