In Revit 2010 the shared coordinate system is now more visible to the user. By default you can click the "Reveal Hidden Elements" button to see the coordinate points. I want to go through some typical scenarios where shared coordinates would be utilized, along with a few quick videos to better illustrate the workflow.
Acquire Coordinates
Common scenario for "Acquire Coordinates" would be where a project file exists such as a CAD or Revit file containing the site information. This linked site file is at the correct location, and will serve as the coordinate system basis. The file would be linked into the main Revit project, and the "Acquire Coordinates" option would be used.
Additional information is in the Revit 2010 Help file, under "Acquire Coordinates". Video example below:
Publish Coordinates
This scenario is used where the Revit project will serve as the coordinate basis. This workflow actually modifies the linked file. For a Revit link, the host project's True North and shared origin are recorded in the linked project, based on the current location of the linked instance. For a CAD link, the shared coordinate system will update the UCS in the CAD file. You will be prompted to save these changes to the CAD file before closing out of the Revit project or after moving the link at any point.
Additional information is in the Revit 2010 Help file, under "Publish Coordinates". Video example below:
Project Base Point and Survey Point
The project base point defines the origin (0,0,0) of the project coordinate system.
The survey point represents a known point in the physical world, such as a geodetic survey marker.
When Shared Coordinates are being utilized, you will see the Survey Point change to reflect the shared coordinate system. For example, acquiring coordinates from a linked CAD file will move the survey point to the origin of the CAD file by default.
The Help files have additional information on these topics and more. I would recommend starting on the "Shared Positioning" page and working through the various topics.

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hi ryan, thanks for posting this. can you also provide some insight to how i would be able to import a civil CAD survey, in which their 0,0 is too far away (say more than the 3 or 4 km Revit allowed max), and get the shared coordinates? the purpose being that I would want to export the Revit floor plan into DWG format so that it comes in the correct location for the civil engineer without moving/rotating any xrefs?
Posted by: John P | August 11, 2009 at 04:59 PM
Hi,
It seems possible to work with larger coordinates that the 1 mile radius. Revit can't acquire coordinates from such drawings, but you can specify them at a given point. The problem we have had is linking Revit files that have such DWGs in them, they will not come in in the right place in linked files, and also when such files are edited or updated Revit 2010 will absolutely refuse to reload them. This is a complete pain when exchanging DWGs with other consultant.
DWGs near origin will work fine, but Autodesk have more work to do on DWGs a distance from the origin before you can use them reliably.
Posted by: Andy Harle | December 02, 2009 at 06:08 AM