[Openstreetmap] Landsat Update = Datum Shift

[Jeremy Stocks]

Took a look at your Southampton Water problem and the words Datum Shift immediately sprang to mind. I often have to solve these problems of old to new datums. (I am working on a Munich based GIS problem at the moment)

I have spent a long time learning this stuff and am stil not expert at it. I warn you it is more complicated than it looks! If I had time I might be able to help. Sadly I do not! :(

If you are editing OS data it is most likely to be in a very old "topocentric" datum or tie point between the map and the earth.

GPS data is collected with reference to the centre of the earth or "geocentric" data.

Acouple of links for you to check this out.

http://soaring.aerobatics.ws/SOARING/BGA/os-note.html

http://www.gps.gov.uk/guide5.asp

http://www.gpsinformation.org/dale/measure.htm

.....and this paper from the chap who really knows what he is talking about....

www.asprs.org/resources/grids/10-2003-unitedkingdom.pdf

I hope this helps!

Jeremy Stocks.
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