Acquire shared coordinates from linked cad file problem

[emmanuelbee]

I have linked DWG cad file of my site plan to a revit model, the linked cad file comes in to the revit model with the correct  orientation (true north) but for some reason when i click on acquire coordinates in order to share the linked model's coordinates to the revit model coordinates, it changes the orientation of the linked file's true north to the revit model's project north and then when I try to rotate it back to true north, i get this error message;

' Shared Sites in the link "18006_SITE_00 (Revit Link).dwg" have been modified, but not saved back to the link. Upon reopening, instances of the link will return to their last Saved Positions. You can Save the link later via the Manage Links dialog'.

Why does the orientation of the cad file change after trying to acquire shared coordinates?  I would have thought if anything, once i  click on acquire shared coordinates, the revit model's orientation etc would automatically rotate to match the linked file's true north and not the other way round

[barthbradley]

I am not following. Is the Link correctly oriented to your view's TRUE NORTH (not PROJECT NORTH)? 

[Anonymous]

I'd guess there is a little confusion with which coordinates systems are being used. There's a lot of posts out there regarding the difference between Project Coordinates, Shared Coordinates, and Internal Coordinates, so I won't get into the weeds with that - suffice to say that 'Acquire Coordinates' is all about Shared Coordinates. When you insert a CAD file 'Origin to Origin' the Revit Origin referred to is actually the invisible Internal Coordinate Origin - so inserting your CAD correctly has no correlation to Shared Coordinates.

Second, a CAD file has multiple UCS possibilities. A virgin CAD file actually has no Shared Coordinate UCS system that is linked with Revit. The first time you link a CAD file with 'Acquire Coordinates', a new UCS will be added to the CAD file that records that position, almost like a link that is 'Shared' by both files. If you move one of the files (the CAD file in your case), they are no longer 'Sharing' the coordinate system. Hence the warning message. If you want to have the CAD file stay where you rotate it, then you need to go to 'Manage Links' > Save Positions (it should be checked 'Positions Not Saved.' Otherwise, the CAD file will go back to where it was when you re-open the Revit model.

After you 'Acquire Coordinates' and Save Position in the CAD file, go ahead and open the CAD file and look at the UCS dialogue box. You'll see a new coordinate system that Revit created.

Long story short, by either acquiring or publishing shared coordinates, you are creating a 2-way dialogue between files, not just a one time info transfer. So, you insert Origin to Origin (not sure which CAD UCS to Revit internal origin) and all looks good, then sync up a newly created CAD UCS shared coordinate system to Revit shared coordinates. This is likely the confusion. Since I'm unsure exactly how the CAD or Revit files were created, I can't produce a direct solution, but hopefully that helps.

[barthbradley]

Actually, I think the explanation is much simpler.  The OP hasn't set up True North yet.   Basically, OP acquired coordinates BEFORE orienting/positioning the Link correctly in the Project.  

[emmanuelbee]

Actually i did set up true north before acquiring coordinates, but after i acquire coordinates, it rotates the building and linked file's orientation to the way it would be if i was in project north, even though the view is set to true north and then when I try to rotate the linked file's orientation back to the way it is orientated when you actually open the cad file that is when i get the error message

[ToanDN]

I would unlink the CAD file, rotate the True North to match Project North, link the CAD file in again, rotate it to match your model, then acquire coordinates.

[barthbradley]

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@emmanuelbee wrote:

Actually i did set up true north before acquiring coordinates, but after i acquire coordinates, it rotates the building and linked file's orientation to the way it would be if i was in project north, even though the view is set to true north and then when I try to rotate the linked file's orientation back to the way it is orientated when you actually open the cad file that is when i get the error message

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I thought you did,  @emmanuelbee. That's why my first question. What I meant by it, was you are saying the Link's orientation in your Project North is not the Link's True North. Of course it isn't.  Change your view to True North and now the Link is correctly oriented; No? 

...I just reread your post and you say in it that you are acquiring coordinates AND THEN  orienting the Link in your Project. That's wrong. ORIENT the Link in the Project first, and then Acquire Coordinates. 

...I'm with @ToanDN: start all over with a clean slate.  

[Anonymous]

Not sure if anyone is still watching this but....

Did you pin the CAD file before acquiring coordinates, I find that gives the behavior described.

Dont pin the CAD file until after you have acquired coordinates.