At 15:27 20/06/03 -0600, you wrote:
>How accurate and repeatable are currently available GPS devices?
Mark,
As someone else suggested, this is an equation where money plays a large
part. If you want true centimetre accuracy from gps then differential gps
is the way to go. See http://www.trimble.com/gps/dgps.html . It is not
cheap...
An interesting new handheld instrument is
at http://www.leica-geosystems.com/gpsgis/gs20/ . This one offers submetre
accuracy, could be enough for your requirements. There's an interesting
graphic of the relative accuracy of various handhelds in the pdf spec sheet
linked to that page. Needless to say it favours their instrument. One
again, not cheap but better priced than the full dgps setup.
Another route is a theodolite. See http://www.theodolite.com/ . Two people
using a theodolite and prism could give you more accuracy than you need at
a more affordable price, particularly if you can find an older (superceded)
instrument which would be quite adequate. To see what has superceded it
look for Robotic Total Station on the website. One man operation and the
option of machine control. That is the option I would pursue if money were
no object, less money than dgps and no issues with satellite visibility.
Finally, if you have three people and three ranging rods you could do all
you need by intersecting sight lines using fixed background objects for
lining up. I was going to suggest trees as suitable backlining points until
I saw the web picture, mountain peaks might be more appropriate. A bit time
consuming but nobody could fault it on cost grounds. An alternative to
backsighting would be to use compasses. You would need to compensate for
variation each year but quite workable.
Try asking at sci.engr.surveying where you will probably find someone who
knows what he's talking about.
Happy surveying,
Nick Brearley
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