Paul Surgeon wrote:

Thanks, that helps a bit.

Am I correct in thinking that TerraGear/FlightGear stores the scenery in wgs84 lat/long format?
From looking at the code it seems that TerraGear does not store the scenery in the OpenGL cartesian format.

To what sort of precision/accuracy do the "geo" routines work to?
15 decimal places like the data type "double"?

In the docs section of the FG web site there is a section on coordinate systems that explains the general FG scheme.

Scenery is stored in earth centered cartesian coordinates, preserving the natural curvature of the earth surface. The one wrinkle is that we define a "center point" for each scenery tile (which is in the full earth centered cartesian coordinate system) and then the remaining points are just offsets to that center point. This allows us to store the vertices in float format, otherwise we would need to use doubles (which don't play well on earth scales with opengl since opengl reduces everything to float which doesn't directly have the precision we need.)


Curtis Olson HumanFIRST Program
FlightGear Project
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