WARNING: This is for mathematically inclined philosophers with some actual ability in the area of spherical trigonometry. This ignorant mendicant of mathematics has discovered that if your intellect is not as long as the lever of Archimedes (which supposedly could move the world), this problem is likely to kick back and flip your brain out between your ears. Okay, with disclaimers claimed, imagine the Irresistible Force traveling on a course around the world. You have been able to obtain two waypoints along its course, and take it as a given that it is on a great circle route. Coming around on a different course (and also on a great circle route) you have the Immovable Object streaking towards its inevitable meeting with its nemesis (well, okay, our imaginary "Immovable" colossus *is* actually moving in this gedankenexperiment, but don't get sidetracked by minutia, allright? This particular I.O. is godfree-mighty, *a priori* massive, and nothing your puny human mind can imagine is going to budge it, I assure you.) Anyway, you have managed to sample two waypoints along its course too. These two great circle routes are not coincident so there are exactly two possible antipodal points where these unimaginable entities could blow themselves to dust (but only after some really cool special effects, I imagine). Anyway, I'd like to sell tickets to the event and make an obscene amount of money, so I need to know where it will happen. So, to boil it down to a boring math problem, we have two pairs of lat/lon points with each pair defining a different great circle. I'd like to know how to calculate the two points where these great circles intersect. (and yes, I've tried searching the net, and came up with lots on solving spherical right triangles, the Laws of sines and cosines, and even Girard's algorithm for solving the spherical surface area... but nobody seems to be concerned about this vital problem concerning the intersection of two great circles.) Is there anyone out here smart enough to solve this one? Reply publicly or privately; I'll summarize *pro bono publico* in a week or so. TIA, - Bill Thoen ---------------------------------------------------------------------- To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
