On Mon, 1 Sep 2008 05:50:42 -0700 (PDT), Silvar Beitel
wrote:

Let me repeat a question I asked before, but was lost in other stuff.

What possible items would you want to do a rough location/elevation on
for a civil engineering project early on that you would do a more
exact location on later? Please bear in mind that you did mention
sewer elevations in a previous post in this thread.

Silvar Beitel wrote:

My brother the civil engineer asked me (the supposed family GPS
expert) about the following scenario (to help in developing initial
site plans without immediately having to go to expensive centimeter-
accurate surveying GPSs and/or bringing in and paying real surveyors,
which would come later on in the process):

Take a pair of cheap identical datalogging GPSs. Park one at a
reference point and let it sit there logging. Send cheapo employee
around with the other unit to the points of interest in the site.
Gather the two and dump out their logs. Match the timestamps, check
that both units used the same satellite set at the same times
(probable over a limited area, like a large construction site?), and
calculate all the relative offsets between the points of interest and
the reference. How accurate would those offsets be? Especially
altitudes (important for things like sewer lines)?

I'm guessing pretty accurate, like down to the resolution of the
units. Say 6 inches for a GPS that reported minutes with 5 digits to
the right of the decimal point.

Thoughts?

--
Silvar Beitel

Basically, it doesn't work. I was skeptical of what is talked about in
this link, but it is true....

http://www.oreillynet.com/pub/a/wire...9/two_gps.html

Also see:

http://www.gpspassion.com/forumsen/t...OPIC_ID=109246