+Lothar69 Posted July 24, 2003 Posted July 24, 2003 I'm new to Geocaching and GPS units in general. Just received an Etrex-Legend for my birthday a few weeks ago. Located my 2nd chache today that was on a man-made bridge elevated about 30 above ground. I'm curious as to how the GPS adjusts the coordinates, if at all for elevations like this. Initially, when I was on the bridge, the distance meter showed that I was within about 30 feet even though I was actually right next to the container (I didn't see it). When I went down to ground level below the bridge, I was able to get to within 3 feet when standing directly below where I eventually found the cache. I think this knowledge might be very useful in finding future elevated caches. Any help would be great! Quote
+Prime Suspect Posted July 25, 2003 Posted July 25, 2003 quote:Originally posted by Lothar69:I'm new to Geocaching and GPS units in general. Just received an Etrex-Legend for my birthday a few weeks ago. Located my 2nd chache today that was on a man-made bridge elevated about 30 above ground. I'm curious as to how the GPS adjusts the coordinates, if at all for elevations like this. Initially, when I was on the bridge, the distance meter showed that I was within about 30 feet even though I was actually right next to the container (I didn't see it). When I went down to ground level below the bridge, I was able to get to within 3 feet when standing directly below where I eventually found the cache. The difference you're seeing has nothing to do with elevation. There are dozens of possible causes for the difference, including the possibility that in the time it took you to walk under the bridge your GPS was able to get a lock on a few more satellites. "Don't mess with a geocacher. We know all the best places to hide a body." Quote
+The Leprechauns Posted July 25, 2003 Posted July 25, 2003 On a recreational GPSr, a small difference in altitude is irrelevant. A 30 foot change in the indicated distance to the waypoint can happen in an instant based on satellite reception conditions. As you find more caches, you'll see that the hider's GPS margin of error plus your own margin of error can mean that the cache is anywhere within a 50 foot circle of where you're standing when the GPS says zero feet. The fact that it went down to three feet for you is probably just a lucky coincidence. x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x Next time, instead of getting married, I think I'll just find a woman I don't like and buy her a house. Quote
Kerry. Posted July 25, 2003 Posted July 25, 2003 The GPS is working in numbers that to many are meaningless. Basically if a GPSr is raised vertically about a certain point (forgetting the affects of a few other issues) the underlying coordinates change in all 3 directions (XYZ) but the conversion to Lat/Long/height only affects the height (if raised vertically and all other things equal) and the lat/Long being horizonatal coordinates effectively stay the same regardless if one is on the ground or 1000's of metres above the ground. What your seeing is normal and has nothing to do with changing height. Cheers, Kerry. I never get lost everybody keeps telling me where to go Quote
+Dave_W6DPS Posted July 25, 2003 Posted July 25, 2003 I think the reason you had an elevation issue is that the site doesn't include elevation data. All waypoints you download from here have nothing in the elevation. As a result, the point being indicated by the GPS may be off by a bit if the cache is elevated. This is one of the reasons for descriptions and hints.... Dave_W6DPS My two cents worth, refunds available on request. (US funds only) Quote
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