CAD X,Y co-ords and OS grids

[yrmuser]

Hi - could someone explain how Ordinate Survey grids relate to X,Y,Z co-ordiantes of model space. We have surveyed positions on a site in eastern europe and the same points on the .dwg site plan match the OS co-ords for that region. Is 0,0,0 in Acad model space relative to the so-called 0,0 of that OS grid?

[Alan Cullen]

No it is not.

You will have to identify a couple of points from the survey that are on your OS grid. Then move/rotate the whole drawing to those correct OS survey points.

[eldon]

If you are not using Latitude and Longitude, you are probably using coordinates from the UTM (The Universal Transverse Mercator Projection). This has 60 individual zones around the world extending 6° in longitude between limiting parallels 80° South and 84° North.

So there are sixty 0,0 coordinates. Each set of coordinates should also accompanied by its UTM zone number, otherwise it is not unique.

The Ordnance Survey grid is a particular one set up for the Britain excluding Ireland. So the coordinates in Eastern Europe have nothing to do with Ordnance Survey.

There is no special relationship between Ordnance Survey and AutoCAD, which has one 0,0 assigned to wherever the user chooses.