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.