Recently I made a ridge flight out of Ridge Soaring in PA, using a Cambridge GPS-Nav for data logging. Having finished the flight with a (safe) land-out, I later wanted to examine in detail what my logged flight path looked like in relationship to the terrain of the ridge. The Cambridge software has no terrain map, but it does include a utility that can turn a log file into a .IGC format that SeeYou can display, and SeeYou has some contoured terrain maps. But this still did not give me what I was after. I found that the contour information in SeeYou's maps was far too coarse.
But I also have a copy of DeLORME's Topo USA 3.0, a program that creates wonderfully detailed, shaded, contour maps on the computer screen or printer. It comes on a series of CD-ROMs or a single DVD disk. I found that TopoUSA has the capability to import a series of fixes as a latitude/longitude text file and will then place a designated symbol at each of those fixes when displaying a map of the relevant area. You can even design your own symbol! I wrote a routine that converts an IGC file into a TopoUSA compatible format, used it on the IGC file of my flight, them imported it into TopoUSA. Eurika!. Finally I was finally able to see exactly where I was flying, relative to the terrain. By correcting the data logger's pressure altitude at each fix based on the known take-off elevation, then subtracting the terrain elevation at each fix (available from TopoUSA), I can calculate fairly accurately (probably within 50 ft or so), how high I was above the rocks or trees at each fix of interest.
If anyone else would like to display flight logs in TopoUSA (highly recommended and instructive for any flight in which terrain is a significant factor) you can email me directly and I will return a copy of the file conversion routine, plus some additional notes on how to proceed. Please DON'T request these via the news group.
If you don't already have TopoUSA, you can see a demo of it at DeLorme's website
www.delorme.com. Disclaimer: I have no connection to DeLORME, except as a delighted customer.
