Subject: | |
From: | |
Reply To: | |
Date: | Fri, 5 Jan 2001 22:45:54 +0100 |
Content-Type: | text/plain |
Parts/Attachments: |
|
|
Mark Henderson schrieb:
> 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).
i don't know - never tried it myself, but you might want to check out:
martin van leusen: the viroconium cornoviorium atlas: high resolution,
high precision non-invasive mapping of a roman civitas capital in britain;
european journal of archaeology vol 2 num 3 dec 99; 393-406 - as i remember it,
they were estimating an error of something like 3 mm over 79 hectares - one
technician plotted about 2000 points over the course of a morning, whereas they
had estimated that 2 could working together on an EDM could only have managed
about 1000 over a whole day -
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!).
and they're all pretty useless underwater - you can't use tapes on a windy day,
EDMs aren't so accurate when it's really cold, etc. - there's always some
drawback -
geoff carver
http://home.t-online.de/home/gcarver/
[log in to unmask]
|
|
|