Heather wrote:
>Perhaps each of you with concerns regarding coordinate accuracy have already
>considered this option, but have you thought about using a total station?
>Their accuracy cannot be beaten and while they are not as convenient as
>handheld GPSes, their accuracy would be worth it for those concerned with
>its compromise in using a GPS.


What someone needs to invent is a system in which the numerous USGS datum
points scattered across this continent are used as stations from which a
portable hand-held instrument is used to record field data, rather than
some satelite some whatever miles away.  Oh, wait, they already have!
        Seriously, though, with all this wonder of having accuracy within 50
meters thrills some of us, it is telling the rest of us, who are used to
dealing with mere centimeters, that we have no use of such far out
"precision."  Is there any sort of system that could be available in which
transmitters are placed at three USGS points (at three obtuse points from a
site) and then readings are taken from the site.  Each transmitter will
give a very divergent reading rather than trying to calculate angles and
distances that vary no more than a few degrees.  Any surveyor worth his
salt would tell you that putting your reference points in a tight pattern
or too far away will give you imprecise or rough results.
        It reminds me of an archaeologist that I worked with a while ago who
placed their transit up on the edge of the field over 500 feet from the
site, shot back at several hundred piece-plots of an artifact scatter, then
expected useful results.  The difference in a single minute of angle can be
many many feet in a long shot like that and there isn't an instrument made
that can reliably provide that type of accuaracy.  That is why we will
continue to use the more "manual" proceeduress to assure accuracy in our
recording and that is why we need trained people in the field who know how
to survey properly and get the right results.  This technology is truly a
wonderful thing, but if we have no idea of how to use it properly it can be
dangerous to what we are trying to do.
        I'm sticking with the Theodolite or EDM.  (What we really need are more
archaeologists who have had a few full-fledged courses in surveying - it is
not something you learn in a 6 week field school - learn the concepts not
just the proceedures.)  (I'm also not saying that GPS does not have its
place in archaeology, for it does, just make sure it is suited for the
purpose and used in the right circumstances) (oh, and I reserve a cut in
any profits from the development of such a system using transmitters at
USGS points, lord knows that archaeology doesn't pay, so I gotta make money
somehow)

        Dan W.






>
>> ----------
>> From:         Howard Beverly[SMTP:[log in to unmask]]
>> Reply To:     HISTORICAL ARCHAEOLOGY
>> Sent:         Thursday, January 04, 2001 11:22 AM
>> To:   [log in to unmask]
>> Subject:      Re: GPS
>>
>> GPS can be a very useful tool, but like all others tools it needs to be
>> implemented correctly.  Three of the biggest problems in using GPS that I
>> have encountered include not knowing the datum for the captured
>> coordinates
>> (are then in UTM, State Plane, Decimal Degree, NAD27, NAD83, WGS72
>> HPGN/HARN, meters/feet ..etc); not applying the correction to the data
>> (before selective availability was turned off); and not tracking enough
>> satellites to give an accurate reading (mostly from hilly/heavy vegetation
>> areas).
>>
>> The following link is to an article about the effect of turning off
>> selective availability on GPS.  Also see GPSWorld, June 2000 for another
>> article on the same subject.
>> http://www.geospatial-online.com/0600/0600divis.html
>>
>> This article gives a good brief explanation on how selective availability
>> affected GPS.
>> http://www.geoplace.com/gw/2000/0008/0800gps.asp
>>
>> And this article discusses the difference between accuracy and precision
>> with GPS.
>> http://www.geoplace.com/gw/2000/1000/1000gps.asp
>>
>> Just some thoughts and suggestions for reading.
>>
>> howard
>>
>> Howard Beverly
>> GIS Analyst
>> Archaeologist
>> System Administrator
>> Wilbur Smith Associates
>> Lexington, Kentucky
>> [log in to unmask]
>>
>