I am trying to convert Lat, Long and Alt (LLA) to Earth Center Earth Fixed (ECEF) because of the lack of XYZ coordinate variables available in the SDK. To do this I needed to know what FS used for a reference ellipsoid, and I came across a possible error. The Creating Terrain and Land Classification document states a polar diameter of 12734.62 km (6367.31 radius). This is grossly out of proportion since even Clarke was much closer back in 1866:Clarke 1866 6356.5838 kmGRS80 1980 6356.75231414 kmWGS84 1984 6356.75231424518 kmIt looks like who ever wrote that FS document just took the polar circumference and just divided it by pi.Can anyone confirm or deny this as an error? If confirmed, do you know what FS does use for the minor axis dimension?Thomas Magma

I believe FS9 uses WGS84.Ian

The SDK states the values Microsoft used. In the absence of any other information why not use those values? Will you be able to tell the difference?

Yes I believe I would notice the difference. It is a difference of up to 10 KM at the poles. That must be a mis-print and I've decided to stick with WGS84.Thomas Magma