This is a response to Noam, post #1119366 - 02/22/08 01:30 PM.

Hi Noam:

I'm glad you can utilize the data that I put together.

I understand what you mean about the original .kml file with the sections in arbitrary order, and also in arbitrary direction. Those were some of the many obstacles I had to overcome in order to synthesize these data.

As for the loops, I'm guessing that the original coordinates were derived from GPS tracks and, when pausing along the trail, the GPS fix wandered around a bit thereby creating 'clouds' where many points were closely spaced and the track formed loops, figure eights, etc.

I work as a software engineer when I'm not hiking so I put together a Python program to process these data. First I searched through all endpoints of the original 4500+ tracks and found those that were closest to each other in order to put tracks together. I thought that was all that would be required but I ended up with lots of errors and strange pairings. Thus began the real trouble.

Essentially all of the anomolies were caused by the loops and clouds of closely spaced points described above. Rather than try to programmatically detect and remove the loops (very difficult) I solved the problem of detecting when lines crossed each other and how to pair them up thereby allowing me to string together long tracks, the ultimate aim, but the loops and clouds remained. I ended up with a few dozen tracks, which I manually massaged to eliminate some and split others into managable sizes, finally ending up with the 39 tracks in the data that I previously posted.

I decided that I wouldn't try very hard to further clean up the 39 full-resolution tracks since they have points that are generally spaced closer together than necessary. Thus many of the loops and point clouds remain.

I translated the full-resolution tracks into .gpx files that may be used with a GPS unit or mapping program. These .gpx files may also be imported into Google Earth. I filtered the .gpx tracks using various criteria, for example spacing the points every 50 feet. This effectively removes the loops and clouds since those points are usually spaced less than 10 feet.

At this time I have an extensive collection of various .gpx files and .kml files for the Appalachian Trail and its shelters. I will be making these files available shortly. I intend to post them on my website guymott.com. (disclaimer: I have no commercial interest, I want to make this large collection of files available to those who can use them in the most effective way possible). Attached is one of these files (in the .zip), a .gpx for the entire Appalachian Trail with points spaced approximately 50 feet and including all shelters with complete information for each shelter.

Again, I'm glad you can make use of these data and I hope that my efforts will help AT hikers and others interested in the Appalachian Trail.

Guy