On Mon, 6 Mar 2000, Alain MORY wrote: > I did'nt clearly expose my problem : A wall must be built above a > foundation that has to be exactly oriented face to south. This wall will > contain an iron armature, so that a magnetic compass will not work > exactly near the wall. > So I thought to give an azimuth to the workers, for example by saying : > the wall must be perfectly aligned with this house angle an with this > treee. > > I thought that it was possible to point with the GPS particular points > around the wanted site. > I will take relatively far points to give a better accurate guideline > (e.g. some mountains twenty km far from my wall) > Is it playable ?
This sounds much simpler than what I originally thought! Using a GPS handset to lay out lines at a construction site would be seriously limited by "Selective Access", the intentional pseudo-random "error" built into GPS. Any position you determine may be off by something on the order of 100 meters. Unless you use a very long measurement baseline, that error makes GPS nearly useless for this type of work. However: You mention mountain peaks ~20 kM from the site. That is a good long baseline to work with! If you have survey maps with sufficient accuracy, you need only define your site's location and that of two peaks, and you can lay out the wal very precisely. If you don't have good enough maps, then use the GPS receiver to locate the points. (Of course, that will require you to travel to those mountain peaks, with your GPS!) Dave Bell W121.9N37.3
