Differential GPS (Yes this is recreational)

Discussion in 'UK GPS' started by Dave Fawthrop, May 22, 2005.

  1. 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*.
     
    Dave Fawthrop, May 22, 2005
    #1
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  2. On Sun, 22 May 2005 09:51:56 +0100, Dominic Sexton
    <{da-sep03}@dscs.demon.co.uk> wrote:

    | In message <>, Dave Fawthrop
    | <> 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/viewpassiverec1.asp?recnumber=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/miembros/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*.
     
    Dave Fawthrop, May 22, 2005
    #2
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