Convert Land Plots to a Different Coordinate System

I had a query recently about how to convert digitised plots of land from one coordinate system to another in Civil 3D. This is similar to a previous post, so here is a different way of doing the same thing effectively with possibly less steps.

First open the drawing with the plots to be converted. Set the current coordinate system in the drawing by using the MAPCSASSIGN command. Then export the polygons to SDF(or SHP or whatever you wish) file format by typing MAPEXPORT. Choose the polygons/layers that you wish to export. On the Options tab you can specify a coordinate conversion as part of the export, see below:

Now in a new drawing (with or without the second coordinate system set), type MAPIMPORT and select the file exported previously and it will import your plots to the new coordinates.

Using Civil 3D to Convert Drawing Coordinates

Thanks to Mark Green of Amicus Technology for the following post....

The example used here converts a drawing from Irish National grid (IG75) to the newer ITM grid.

Setting the coordinate system of the Irish Grid drawing

1. Open the drawing you wish to convert from IG75 grid to ITM grid

2. At the command prompt type ADESETCRDSYS and Enter

3. In the Assign Global Coordinate System dialog box click Select Coordinate System

4. In the Select Global Coordinate System dialog box select Eire-Ireland from the Category drop-down list

5. Under the Coordinate Systems in Category list, select Ireland1965.ING Irish National Grid referenced to Ireland 1965 (note that this is IG75 grid)

6. Click OK and OK again

7. Save and close the drawing

Setting the coordinate system for the ITM drawing

8. Start a new drawing using the Acadiso.dwt template

9. At the command prompt type ADESETCRDSYS and Enter

10. In the Assign Global Coordinate System dialog box click Select Coordinate System

11. In the Select Global Coordinate System dialog box select Eire-Ireland from the Category drop-down list

12. Under the Coordinate Systems in Category list, select ITM Irish Transverse Mercator 1995 with ETRS89 Datum:Ireland

13. Click OK and OK again

14. Save the drawing with a new name e.g. project123-ITM.dwg

Converting the IG75 drawing to ITM grid

15. At the command prompt type MAPWSPACE and Enter twice. This opens the Map TaskPane

16. In the Taskpane palette select the Map Explorer tab.

17. Under Current drawing, right-click on Drawings and select Attach

18. In the select Drawings to Attach dialog box, click in Look in to navigate to the folder with the

IG75 drawing

19. Select the drawing, click Add and click OK

20. Under Query library, right-click on Current Query and select Define

21. In the Define Query of Attached drawings dialog box, under Query Type, click on Location

22. In the Location Condition dialog box, under Boundary Type, select All and click OK

23. Under Query Mode ensure Draw is selected and click Execute Query

24. The drawing objects from the IG75 drawing should now appear but with ITM coordinates (check Grid Inquest program to verify)

25. Save the drawing.

Footnote: There is a common misconception that the Irish national grid system in common use is based on the 1965 adjustment. In fact this was only used for a short time and the readjusted 1975 network, referred to as IG75, is the basis for the pre ITM grid system. This misnaming appears in Autodesk MAP 3D and Civil 3D and MapInfo software among others. The difference between the 1965 and 1975 grids is up to approx 13 metres.

In MAP 3D and Civil 3D it is essential to select the coordinate system named

Ireland1965.ING as this is the correct 1975 grid while the coordinate systems named TM1965Irishgrid and TM1965Irishnationalgrid are the 1965 grid.

Civil 3D Point File Coordinate Conversion

Its not uncommon to have a drawing which is at one coordinate system and for the same project to have a survey that was undertaken to a different coordinate system. You need to import the point file from the survey into C3D so that it appears at the coordinate system of the drawing.


Firstly you may have already seen the tick box in the import points dialog box to 'Do coordinate transformation if possible' (see image). Just ticking the box will have no effect without a bit of setting up first. This is where the 'if possible' bit comes into play. In order for C3D to perform the transformation it needs to have a coordinate system defined in both the drawing and on the imported point file. When you import points and tick this box C3D will transform the points to the coordinate system of the drawing.

Assigning the coord sys to the drawing is straight forward. Type MAPCSASSIGN at the command line and select. In my case for Ireland the drawing is to ITM. You can use the filters here to help you search.

Next we need to define the second coordinate system on a new point file format which we will then use to import the point file.

First open the import points dialog - click on points menu<Import/Export points<Import points.

In this dialog box click on the icon in the image below to create a new point file format.This is made easier by making acopy of one that already matches the format of the point file you are going to import.

In the point file format dialog box set your default file extension and the coordinate system of the point file. The next bit is very important... you must make sure that that the columns for easting and northing are set to Grid Easting and Grid Northing otherwise the conversion will not work and cue hours of frustration!

With the point file format set up and back in the import points dialog box browse to your point file, selct the point file format just created and then tick the box to do coord transform and that should be it!