Geographical locations not scaling correctly autoCAD

[Fred_vanEesteren]

I've been trying to use the Geographic locations to put a map in the background of surveyed data, however, when completing the process of geolocating, the Bing maps are not scaling correctly. The Initial insertion point matches my surveyed point but the further away from the point you go, the worse the match compared to my surveyed data.

I don't think it's a Coordinate reference system mismatch as my data was captured using OSTN15 and therefore I selected this CRS when geolocating.

[pendean]

Show your work: share that DWG file here please.

[Fred_vanEesteren]

insertion point is correct but as you can see the further away you get the more the Bing map deviates from my surveyed data

[pendean]

I may be missing it, do you mean if I do this for example or something else (they appear consistently off all the time)

Your DWG file's units are set to millimeter, was that deliberate?

[Fred_vanEesteren]

Correct, all of these features should line up with the image (bunker  outlines)

no it's not deliberate that my drawing set to mm, but I've changed it to meters with the same outcome.

[Pointdump]

Hi Fred,
Welcome to the Autodesk Forums.
OSTN15 is not a Coordinate System. It is a Geodetic Transformation between the Datums used by ETRS89(GRS80 Ellipsoid) and OSGB36(Airy30 Ellipsoid). The mismatch you're experiencing is a difference of Datums. Things look pretty good on my screen. "OSTN15.NationalGrid" shows up on my Status Bar but I can't find it in my MAPCSLIBRARY.
Dave

[Fred_vanEesteren]

Hi Dave,

Any idea how i can remedy this?

[Pointdump · Accepted solution]

Fred,
Vanilla AutoCAD is not dealing with the Datum Transformation necessary to match your linework with Bing.
If you have a current subscription to AutoCAD, you can grab Map 3D at no charge. That's your best bet.
Dave