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REVIT : DWG link with georeferenced data

REVIT : DWG link with georeferenced data

Hello,

Full explanations, please have a look to attached file.

Most of the time, Revit using use georeferenced dwg background coming from surveyor.

Below customers follow this workflow:

  • Insert / Link CAD’ to link the DWG with ‘manual center’ as positioning option, and move the DWG around the internal origin
  • choose a surveyor’s terminal as a reference in the DWG and move the DWG to have this terminal on the internal origin – pin the DWG
  • unlock “the survey point” and two solutions are possible:
    • move the survey point to the surveyor's reference
    • move the dwg file the surveyor's reference the the origin
  • use the “Acquire Coordinates” and click on the DWG file
  • go on a section view, use the “Specify Coordinates at Point” and click on a level to give the real altimetry of the surveyor’s terminal

We can now check if the survey point’s coordinates are the same than those of the surveyor’s terminal (X, Y,Z)

By the way, now after acquisition, the survey point finds himself so far from the BIM model (because by default “the survey point” is placed to the 0;0;0). In this case, the customer must move the unlocked survey point (not losing right coordinates) to bring it back on the surveyor’s terminal.

 

Propositions : ==> more info in attached file

1- “The survey point” stays at the same position with right X, Y and Z coordinates :

Regarding workflow described before, it will be very powerful by using “Acquire Coordinates ” feature and by default the “survey point” stays at the same place but acquire X,Y, Z* (not moving to 0;0;0)

* Z coordinates aren’t taking account from the surveyor plan

2- “Specify Coordinates at Point” :

It could be also very useful and time saver to adopt the same mechanism as explained prior for “Specify Coordinates at Point” feature. The “survey point” stays at the same place but acquire Z

3- Export Base point, survey point, internal origin

It could be very useful to export the base point, the survey point and the internal origin in DWG because tiday we have to create specific objects to see their location in a DWG.

2 Comments
samuelsanf
Advisor

My work flow for inserting DWG with coordinates for Revit new projects is:

 

  1. Link the CAD center to center
  2. Rotate the CAD according to desired Project North.
  3. Relcate the CAD as near center position I can (if there is a property line, move one of its vertex to the revit internal origin)
  4. In elevation, section or 3D View move the CAD down (or up) to match default revit "Level 1" with the desired survey elevation (contour) to be used as Ground Floor 0.00 datum (so survey point elevation 0.00 is lower). see mitune 0:22 to 0:27 of attached video.
  5. Pin the CAD.
  6. Acquire Shared Coordinates from CAD.
  7. Remove the shared position to the CAD. Not only is anoying that every time we save/sinchronize the project revit ask to save back the CAD, but saving back the CAD modifies the CAD every time and changes it coordinates accordin to Revit orientation so Revit coordinates changes too, and so on. It's a terrible Issue.

 

With steps 1 to 6 I'm happy. Step 7 is really a problem, revit should not writte back coordinates to the original DWG.

 

The specify coordinates at point let you only change the Z value if you pick a level (XY Plane) in Revit.

 

 

SteveDFThorne
Collaborator

Not sure if this helps you but I have found that I always leave the survey marker unclipped no matter what and it has helped simplify the process. I often wonder if Autodesk should just make it unclipped by default and remove the paper clip all together. It confused me for a couple of years when my survey marker would teleport a great deal  away from 0,0,0 and wreak havoc on zoom extents. Maybe I have forgotten the need for the paper clip after years of having it unclipped by default.

 

Using ACC BIM Collaborate Pro you can only acquire coordinates anyway and not publish them so that helps with another point. I guess this is because of a major performance issue so we may never be able to push coordinates anytime soon when using the newer process. I'm not sure if this applies to AutoCAD files though. 

 

I wonder if it is just my region's coordinate system, but I find I have to create a separate Civil 3D file that has been re-referenced (manually re-located in a structured way) closer to 0,0,0 or when it is linked into Revit all of the linese will go zig zag and have very strange distortion making it hard to align. These means I have only two options for acquiring coordinates: 

  1. I can get them from a Civil Published Surface with the Link Topography tool (which requires that I already set coordinates at point, usually in a civil / landscape Revit file) 
  2. Set coordinates at point

I wish this linking distortion problem was fixed though, because that would be very efficient compared to what I have to do now. 

 

Does your geo-referenced CAD file come in without distortion? 

 

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