For one reason or another drawings sometimes need to be moved from one coordinate system (datum) to another.  A classic example may be moving from a NAD 27 datum to a NAD 83.  Whatever the case may be, how might one perform this translation as accurately as possible?

To answer that I turn to good old Map 3D.  As you may know both AutoCAD Land Desktop and AutoCAD Civil 3D are built on top of AutoCAD Map 3D, so if you have either product, you also have Map 3D.  Users of Map 3D naturally know it’s power, whereas I have found many civil engineering professionals nearly forget about the Map menu altogether.  While it may seem odd, we’re actually going to start the translation from a blank drawing.

  1. Start a blank drawing
  2. Using the "Map Classic" workspace, go to Map > Tools > Assign Global Coordinate System.  From here we’re going to assign the datum to translate your existing drawing to. 

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    In this example I have a drawing in NAD27 Virginia State Plane South (VA-N), and want to move things to NAD83 Virginia State Plane South Feet (VA83-SF).  That being the case I will enter VA83-SF as my code.  The [Select Coordinate System] button will also allow you to browse for any of the included coordinate systems.

  3. With my coordinate system set, I will now open the Map Task Pane.  If it is not already open, you can use the MAPWSPACE command to turn it on.

  4. From the "Map Explorer" tab Right-Click on "Drawings" and select "Attach"

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  5. The resulting dialog will allow you to browse to your original drawing in the other coordinate system. Once you have found the drawing you with to convert, select it and press the [Add] button.

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  6. With our drawing attached, we can now go about configuring a query.  To do this right-click "Current Query" from the Map Explorer Map Task Pane, and select "Define".

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  7. From the resulting Define Query dialog, click the [Location] button under "Query Type", and then [Ok] to accept the "All" Boundary Type.  What this means if we’re going to query the original drawing in its entirety. With the "Query Type" defined, select "Draw" as the "Query Mode"

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  8. After defining the query, press the [Execute Query] button.  Once AutoCAD Map 3D finishes processing, do a Zoom Extents and you should see your translated drawing.

It’s worth mentioning that some LDT/Civil 3D objects don’t like being moved like this.  I have run into issues with AeccPoints, as well as Civil 3D Parcels.  Civil 3D Parcels for instance refuse to move away from where they were first defined.  In such cases your only real option is to explode the parcels, perform the translation, and then redefine the parcels using Civil 3D.