can you use a gps to form a straight line betwenn two known points... just got a piece of property and need to put up a fence .... lots of trees so i need to get a line of sight without too much cutting.... thanks.dave
Joined: 05 Jun 2008 Posts: 12415 Location: New Jersey
Fri Sep 12, 2008 2:03 pm
I'll second what has been said. I own wooded land and have played around a lot with various GPS'es to survey it. You will get a pretty good idea of your boundaries, but nothing very accurate. If you mark 4 or 5 waypoints along your property line, it's very unlikely that they will all form a straight line. Then if you return the next day to the exact same points, they will be different.
Visualize a circle with a radius of 10 meters (~33 feet), with the true location of a point at the center. At any given time, the GPS will give you readings which should fall somewhere within that circle. The worst case would be readings at opposite sides of the circle, so from one day to the next, these readings could differ by as much as 66 feet and still fall within the advertised accuracy of the GPS.
Now my property borders on a densely wooded state forest where few people go, and there were no existing property line markers. Not likely that anyone will care much if my line is off by 20 feet. But if there was another house on the other side of the line, that would be a different story.
I believe there is computer software which lets you take readings over an extended period of time and get a very accurate fix, but that won't help if you're trying to walk around and find your property line.
Here's what I'd suggest if you just want to play around a little. If you go on Google Earth, are there some landmarks which would let you draw your property lines on the map? I was able to do that since the lines are defined by a relationship to a couple roads. I was able to get the coordinates of the property corners fairly accurately that way, and I then created waypoints on my GPS to match them. I then created a "route" on the GPS which passed through these points.
After doing this, I could walk around the woods and see my position displayed in relation to the pink route line (I was using a Garmin GPSMap 60csx). Still subject to the accuracy limits discussed above, but it gave me a pretty good idea of where the line was in the dense woods.
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