I responded directly the other day, but thought I would post to the list
as well. I'm a GPS engineer and spend most of my working time analyzing
data from GPS receivers. I've also tried to use these things for
surveying projects with very limited success.
While it is true that the removal of "selective availability" greatly
increased the reliability of civilian gps, it still requires a great
deal of patience to use this technology for anything like surveying.
What you generally see as a location fix on your hand-held gps receiver
is the result of filtering a large number of individual raw fixes. This
works very well if you are driving down the highway, reasonably well if
you are driving at lower speeds, and tolerably well if you are on foot
or standing still. Even if you dismiss rogue fixes, you're still going
to have a fairly wide circle of uncertainty as you could see if you have
a look at the link below.
A lot of people may tell you different and may have used gps under
conditions where these errors average out, but this is definitely not
the ideal technology for your application. On the positive side, if you
know the precise altitude of your location (which you would usually be
able to determine if your site is also an airfield), you can get a good
fix with fewer satellites and so more quickly or under a wider range of
conditions. But the closest you will still be able to come is probably
setting up the "average position" setting on a Garmin receiver and
spending quite a long time with it at each pylon location.
But I encourage you to try a simple experiment. Take your receiver out
somewhere this afternoon and mark a spot with it. Then come back
tomorrow and mark the spot where the receiver says you were the day
before. Measure the distance between them and think about whether this
would be good enough for setting up a course.
Regards,
Stuart
http://www.visualgps.net/VisualGPS/VisualGPSprt.pdf
Marcel Chichak wrote:
>Quoting Phil Buttolph <pb1@humboldt.edu>:
>
>
>
>>We use GPS to locate dive sites for research...my information may be dated,
>>
>>
>
>I think your information is past its best before date. The military selective
>availability error was turned off about 2 years ago, thereby allowing metre
>horizontal accuracy.
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