I hope to survey the position of cup and ring stones on Rombald's/Ilkley
moor and other places in the West Riding to an accuracy of 1m. There are
a couple of web sites which list this sort of thing, and I would wish They
have already been surveyed to 10m and have an 8 figure National Grid
Reference (10m) published in Prehistoric Rock Art of the West Riding
http://www.alkelda.f9.co.uk/wybook1.htm giving details of some 600 of these
stones, of which I have a copy on order.

They are however stones, some less than 1m dia. and 1m high, in the middle
of a featureless heather moor, and the heather is normally knee high, and
if it has not been burned recently to provide food for grouse, can be thigh
high. Searching a 10m square area is a bit of a pain, though much less
of a pain than searching a 100m square.

As my ordinary Garmin Etrex often gives a positional accuracy of 4m, and
other GPS receivers are probably just as accurate. If others have a 10
figure (1m) National Grid Reference and a receiver giving 4m accuracy they
should in theory only have to search a 5m square.

I have got myself a username on http://www.gps.gov.uk/ and am ploughing
through the information there.

Has anyone any experience of differential GPS?

--
Dave Fawthrop <dave hyphenologist co uk>
Beware of anyone posting X-No-Archive yes,
they must have something to hide or something to be ashamed of.
Your task, should you wish to accept it, is to determine *what*.

On Sun, 22 May 2005 09:51:56 +0100, Dominic Sexton
<{da-sep03}@dscs.demon.co.uk> wrote:

| In message <(E-Mail Removed)>, Dave Fawthrop
| <(E-Mail Removed)> writes
| >I hope to survey the position of cup and ring stones on Rombald's/Ilkley
| >moor and other places in the West Riding to an accuracy of 1m. There are
| >a couple of web sites which list this sort of thing, and I would wish They
| >have already been surveyed to 10m and have an 8 figure National Grid
| >Reference (10m) published in Prehistoric Rock Art of the West Riding
| >http://www.alkelda.f9.co.uk/wybook1.htm giving details of some 600 of these
| >stones, of which I have a copy on order.
| >
| >They are however stones, some less than 1m dia. and 1m high, in the middle
| >of a featureless heather moor, and the heather is normally knee high, and
| >if it has not been burned recently to provide food for grouse, can be thigh
| >high. Searching a 10m square area is a bit of a pain, though much less
| >of a pain than searching a 100m square.
| >
| >As my ordinary Garmin Etrex often gives a positional accuracy of 4m
|
| That is a guesstimate of the accuracy based on the satellite signals
| used by the receiver. It cannot be relied upon. The only way to really
| know the accuracy at a given point and time is to compare the
| co-ordinates reported to accurate co-ordinates for the point.

The OS give have many stations surveyed to a ridiculous accuracy on
http://www.gps.gov.uk/viewpassiverec...umber=C1SE0945
Registration required. This is the one I will use, being a few km from
where I will be working.

ETRS89 Cartesian ETRS89 Geodetic
X: 3764259.283 m Latitude: 53° 54' 9.3367'' N
Y: -121892.621 m Longitude: 1° 51' 16.8450'' W
Z: 5130708.688 m Ellipsoid height: 426.877 m

National Grid (converted by OSTN02/OSGM02)
Eastings: 409646.018 m
Northings: 445166.928 m
Height: 376.472 m (Orthometric height above MSL, Newlyn Datum)

| >, and
| >other GPS receivers are probably just as accurate. If others have a 10
| >figure (1m) National Grid Reference and a receiver giving 4m accuracy they
| >should in theory only have to search a 5m square.
| >
| >I have got myself a username on http://www.gps.gov.uk/ and am ploughing
| >through the information there.
| >
| >Has anyone any experience of differential GPS?
| >
|
| If you have access to a laptop or PSION 5 you can log the raw data from
| the eTrex and post process it against the data available from
| gps.gov.uk. With 2 to 5 minutes collecting data at each point of
| interest you are likely to be close to 1m accuracy. The longer you
| collect data for the more accurate the end result will be.
|
| See
| http://artico.lma.fi.upm.es/numerico...antonio/async/
|
| and
|
| http://mywebpages.comcast.net/dmilbert/softs/index.html

Thanks Those will take some study.

--
Dave Fawthrop <dave hyphenologist co uk>
Beware of anyone posting X-No-Archive yes,
they must have something to hide or something to be ashamed of.
Your task, should you wish to accept it, is to determine *what*.