getting cad coordinates and checking export from revit

[Philipp Kühne]

Hello,

I am beginning to grasp the idea of "specifing coordinates at point revit". I am working on quite a large scale project and as usual the point 0,0,0 on the surveyors Cad files is miles away from the actual drawing. The usual solution is to redefine a new UCS close to the drawing, which I did.


It seems to be quite practical to give a point in revit the same coordinations as in a project relevant Cad file. So far okay. However, once rexported into Cad, my file does not appear on the same 0,0,0 as the Cad. In fact the DWG appears always close to the "invisble" origin in Revit - so to say the first position where I put it. Am I missing out on something ? Do I have to unlock the Project Base Point before doing "specifing coordinates at point revit" ? I realised, no matter what coordinates I give within the "specifing coordinates at point revit" the DWG rexported into format DWG stays in the same initial position. Which for me is quite troubling as I have to communicate my plans in CAD to partners, etc....

Any help would be great !!

Thanks

[Steve_Stafford]

You need to specify Shared Coordinates when you export the file(s). It's part of the Export Settings dialog on the Units & Coordinates tab

[Philipp Kühne]

Hi Steve,

Thanks, great- seems to work. I would have never found it !!!

One thing makes me a bit suspicious: If I insert my exported file into the original cad file at first sight everything seems to match. the 0,0,0 is well placed lines are overlaying, etc. However zooming in I detect a tiny offset between the xref (the revit export) and the original cad file. It's around 0,0004m - I know it's rediculously small. If I dimension it, the dimension indicates 0.

In other cases I see an offset measuring it with the "distance" commande results in 0. Is this a problem of sight - let's say graphic card, etc.

I am inquiring because our site is quite large and ingeneers can be quite picky on these tiny offsets.

Thanks again

[Steve_Stafford]

Sounds like you are experiencing large coordinate values and distance from origin. The display of graphics will distort when very large values are involved..

Just to be certain, you could mock it up again in a new project file.

Insert the DWG file using Positioning-Auto-Center to Center
Move the "center" of relevent portion of your site near the Revit origin
Select the Survey Point icon
Unclip the paper clip icon
Drag the icon to a known benchmark (find out the coordinates in acad)
Use Specify Coordinates at Point
Select the survey point
Enter the coordinates.
Save the file
Creat some Revit elements to export
Export using shared coordinates
Check results

[Philipp Kühne]

Hi Steve,

I haven't tried out your counter check. The thing I don't get is that my survey point will become the equilant of 0,0,0 in cad by doing specify coordinates at point. In this particular case the 0,0,0 in cad is miles away - around 600 000 m. So in order to bring the cad drawing in the first place I had to move the drawing close to 0,0,0. How could I in revit define a point in the mids of nowhere to be 0,0,0 ?

Thanks

[Philipp Kühne]

Hi Steve,

This is what made the difference.In the first place I had taken a point as a reference on the dwg which was significant in terms of architectecture (corner of a tower), yet random in terms of geometry and quantity surveyor. So this point was something like 590320,1234 x 132540,0178.... lot's of figures behind the comma.

In a second time I had taken a point without any figures behind the comma and thus on the surveyor grid. Rexporting into dwg I had no difference anymore or very neglectable (0.0001m).

So better take points which are straight !

[Steve_Stafford]

Glad you got it sorted!

[zride91]

I am also struggling with Revit Export to DWG for site coordination. The process is literally driving me insane.

We have a site plan in DWG, where as Walter's case is no where near the origin. I linked it into our Revit 2012 arch model, moved it to where the common point in site and our building matched, moved the project and survey base point to this common location, and specified the coordinates and elevation indicated in the DWG site plan. I have adjusted the elevation and everything looks great in Revit. When I export, I use the shared coordinates, export a 3D view with everythign simplified and all site stuff turned off, and I get a DWG.

**This is where I begin to loose it**

When I open the DWG site plan in AutoCAD 2011, then XREF the exported 3D arch model, the XREF comes in no where near the site plan... However, when I open the exact same DWG site plan in AutoCAD Civil 3D 2011, then XREF the exact same exported 3D arch model, the XREF comes in EXACTLY where it suppose to. ALSO, if I open up the exact same DWG site plan in MicroStation V8i SS2, then reference the exact same exported 3D arch model, it too comes in EXACTLY where it suppose to. Also, if I do this same thing, with the same files while running Civil 3D as AutoCAD, things get placed in the right locations too. It is just when I reference the plan in a Vanilia AutoCAD install!

I can't imagine why things are different in AutoCAD than Civil 3D... If anyone can help me maintain my sanity, it would be much abliged.

Also, just a side note... When we referenced the plan in MicroStation it was off a LITTLE bit originally, but this was due to Survey Feet/Imperial Feet, which was very easily fixed in the Open DWG settings in MicroStation.

[Steve_Stafford]

First guess is import units are set differently.

[zride91]

Steve, import units?

I am not importing anything. The exported DWG is coming in differently to Civil 3D than it is to AutoCAD. Did you mean insert units? If so, that was the first thing I checked too, and they are both the same in AutoCAD and Civil 3D. Thanks for the reply. This may be more of a AutoCAD issue than Revit, so this post may be misplaced. Sorry.