Inserting a Spatial reference

[eddlewington]

Full version AutoCAD 2025.

I'm being asked to provide a .dxf with a spatial reference for conversion into a .json file by someone else but don't know where to start.

Currently I have an Ordnance Survey scale base map (Based in UK) and various pieces of geometry on top of the map. Can anyone link me to a guide or explain how I go about generating a spatial reference and including it in the .dxf which I will send for conversion into the required .json format.

Thanks!

[ChicagoLooper]

Hi @eddlewington 

The guidance you are looking for will vary because it depends on the map you start with--there are many, too many, variables. 

Please provide more info. Can you share your Ordnance Survey scale base map for analysis? If it has enough info, hopefully it does, then a procedure can be provided. Without that survey no meaning instructions can possibly be offered.

Also AutoCAD are you running? Version and release year?

Feel free to use private message if you wish.

[eddlewington]

Thanks for the reply:

• AutoCAD Full 2025
• Original File attached.

[eddlewington]

Original file

[ChicagoLooper]

Hi @eddlewington 

Thank you for sharing.

National Trust, Arrington, correct?

You don't need to move, scale, or rotate your drawing. You can save your original drawing to dxf. Also, copy the info that's shown below (blue text) then paste it into Word, Notepad, or directly into the body of an email—it should accompany your dxf when you send it. If you need more geospatial assistance, just ask. 

As noted earlier, your drawing is already spatially accurate. You don’t ‘technically’ need a georef'd dxf file b/c your coordinates are already consistent w/OSGB 1936 grid but I’ve attached a georef’d dxf anyway.

The georeference is

OSGB 1936.NationalGrid (meters)

EPSG 27700

To get a non-gepref’dxf (yes, it’ll work even if your saved dxf is not geospatial):

Use SAVEAS=>then save with .dxf extension (refer to image below). 

Unfortunately AutoCAD  cannot Import nor Export json. So for your specific need the dxf format is the most AutoCAD can do. 

Here's a small portion of your drawing. Bing imagery is in the background.