Monday, 13 February 2012

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!


  1. Muchas Gracias,

    This post has been very useful for me :)

  2. And here I am, years later, finding the article incredibly useful still. Thanks very much!