[sac-forum] Re: GPS

On Tue, 30 May 2006 14:34:37 -0700, Stan Gorodenski wrote:

> This may appear off topic but it revolves around astronomy on my lot. I 
> would like to know accurately the location of the sides of my lot, i.e., 
> perpendicular to the road. I have discovered that there is a 'surveyor' 
> type GPS unit that is accurate to 1/300ths of a foot. However, I doubt I 
> could rent one because I think they are very expensive. Do GPS's exist 
> for the non-surveyor citizen that is accurate to within plus or minus 6 
> inches or a foot?

GPS surveying is typically done with differential GPS.  This has one unit
that sits on a survey mark, broadcasting to the other its offset from the
GPS location.  This can be extremely accurately.

You might try using two GPS's over two survey marks, at the same time
(two people) and test how accurate this can be.  Even a test case at
either end of a 100-foot rope would provide interesting data (can you
measure the rope?).  More than likely, you'll need a pair of identical
GPS units to eliminate any software bias with the signal capture (eg does
the unit capture when you press or release the capture button).

There was an article in EVAC's newsletter around 1995 +/- 2 years from
Sam Herchak.  He reported on a large number of captures to work around
selective-availability.  There was a plot with the results.  This was
with just until though.

        -Paul

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