Mark Branstner- I agree with your two points, but I think the really
important conclusion about the use of GPS for fine grained mapping of
centimeter or sub-centimeter relative accuracy is the time it takes to
collect the data using a Trimble.  Collecting 100 or more points for
each point and then correcting the data by post processing can be far
more time consuming than using an EDM, tape and compass grid, plane
table and aledaide or other method.  The cost of labor then is more the
consideration than the cost of the instrument if one is plotting more
than ten or so artifacts in a relatively compact (say less than 100 m
diameter area).  There is however a middle range of site types where I
have found the Trimble to be my instrument of choice.  For plotting
sub-datum points for 30 or so rock art panels dispersed over a 500m x
500m area and for collecting locations of sub-datum points for
structures on historic sites where there are 10 -50 features in a 250 m
x 250 m area the Trimble is more efficient than other non-GPS methods
for a similar level of relative location accuracy between features.  In
both the rock art project and the historic site project we were able to
rapidly place sub-datums and then make detailed maps within these large
areas using tape and compass methods, which were adequate for our
objectives.  Finally, I hardly need to point out that any GPS is pretty
worthless in a rock shelter or a deep canyon and I have been led to
believe in some tall timber/close crown cover environments (the last not
a major problem in my part of Nevada!). -Mark
Mark Henderson
Ely, Nevada

[log in to unmask] wrote:

> Heather,
>
> I think there are two questions/methodologies being argued here:
>
> (1)   Actual internal site mapping, which is in most cases better served by
> the total station or standard surveying technique approach, and
>
> (2)   Mapping site locations within the broader landscape, which is
> typically
> better served with good GPS data, without the necessity of shooting-in from
> some known point.
>
> Clearly, we are approaching the point where actual excavations and internal
> site structures may be mapped in with GPS, but I think that most of us
> would
> want sub-centimeter accuracy for such a recording technique.  Given that
> Trimble GeoExplorer III is suggesting only barely sub-meter accuracy for
> around $3500, the cost is going to have to come down a long ways before
> this
> is really an option.
>
> Mark Branstner
> Great Lakes Research, Inc.