On Sat, 3 Mar 2012 18:47:56 -0000, wrote:

GPS 3 meter error

Yep. However, standing under the tower, in order to take advantage of
this level of accuracy is often impractical. Climbing barbed wire
topped chain link fences is not my idea of fun. I ran into the
problem when I was throwing together a map of the local cell sites:
http://802.11junk.com/cellular/ (from about 2002).
I had a suitable GPS, but I couldn't get anywhere near some of the
towers in order to get an accurate position. I had to record a GPS
location nearby, measure or estimate the distance and direction to the
tower, and then do the math.

I forgot to mumble something about HARN and NAVD88, if the best
possible vertical accuracy is required:
http://www.ngs.noaa.gov/faq.shtml

Also, all the major mount tops have benchmarks pounded into the ground
somewhere. If you can find the benchmark, you have the location, and
sometimes the altitude. For example, for Mt Hamilton:
http://www.waymarking.com/waymarks/WMQ1J_Mt_Hamilton_1960_ECC
The problem is that mountains tend to move every time there's an
earthquake. Even without earthquakes, the distance between Mt
Hamilton and the Farallan Islands moves about 5 cm per year across the
San Andreas fault.

I think this might help if you're trying to locate a tower on Mt
Hamilton:
http://www.ucolick.org/~sla/mtham/gpos.html
"The vertical positions are not as well known and may
be off by 10 meters. "
Well, maybe not...


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558