Pete wrote:
What cartesian coordinates? Surely the position in the world, whether in the real one or in FS, is by Latitude/Longitude/Altitude. The whole mechanics of FS's position system is based on something abbreviated to "LLAPBH" -- the six degrees of freedone, Lat, Long, Alt, Pitvh, Bank, Heading.
Cartesian coordinates are only valid on a flat space and you also need to specify your origin position (in the real space being simulated) and the relative orientation of the x,y,z axes. If you have your own such reference, then the conversion from LLA is a matter of spherical trigonometry.
To explain my position better (and with all due respect; none of this is meant to sound flippant):
Right or wrong, many sims I've had to work on over the years (including the one that's currently giving me a big headache) have operated in "flat world" in a fairly localized gaming area, over a flat database, using a cartesian grid with some arbitrary origin. Obviously there has to be some mapping involved to relate this flat grid to geodetic earth coordinates, such as UTM, Lambert Conformal Conic, or whatever. Another variable is the datum in use, e.g. WGS-84, which defines the earth's ellipsoid parameters. All of these things contribute to how geodetic earth coordinates, e.g. lat/lon/elevation turn into linear distances, and also affect the reckoning of true heading since meridians are rarely oriented "up and down" the grid.
In other words, except in the most naive case the math is interesting but is also more involved than spherical trig. If you don't have the exact algorithm, map parameters, and datum, then it's nearly impossible to get accurate relative linear distances starting with geodetic (and x/y/z relative linear distances are what I'm ultimately needing).
In the best case everybody agrees on what the earth looks like, and uses ellipsoid databases and the motion models fly over the ellipsoid earth model. Even in that case it's common to still have a cartesian system that's centered on the earth and stuck to it, such as the DIS geocentric coordinate system. I.e. the world doesn't have to be flat for a cartesian system to still be relevant.
The bottom line is that there are still plenty of cases where flat world is still alive and well, and unfortunately I've had one of them dropped in my lap, and it's causing me to need to know exactly how to turn MS Flight Sim's geodetic coordinates into some cartesian system such that accurate relative distances (or more to the point for my current problem, reasonably accurate lines-of-sight) between points can be reckoned given the lat/lon/elevation of those points.
I've encountered at least one amateur source who claimed that MS Flight Sim's databases were indeed flat, and the mapping was some modified Lambert Conformal Conic (see http://www.saunalahti.fi/masunta/FS-ATCation.html in the section titled "Microsoft Flight Simulator 4.0 coordinate system"). But this document is old, for an old version of MS Flight Sim, and the guy that wrote it (whom I exchanged email with this morning) said he never quite figured it all out. He also said that the Mallard guys were the real source of the answer, but I haven't tried them yet.
As thorough as you have been at gathering up all the other data made available by the FSUIPC stuff I assumed that if this data were available you would have included it, but I thought I'd ask anyway.
Thanks for the input.
Rob