Coordinate system CAD collaboration - Revit nightmare

[SamuelAB]

Architects send us up to date CAD plans from Revit every few months.

Here is our issue. We've been working in this manner for over a year and the CAD plans they are sending us sometimes move. Since they are xrefs, we just align them but we want to find the best practice to this so that there is no movement. We could eventually be the ones giving these types of files to other consultants so we want to know what the best way to do this is.

Right now they are exporting Sheets to DWG using Internal Project coordinates.

I know that they should be exporting Views using the Shared coordinate system. When I tried this, all the CAD drawings came in slanted to the true North. I am not sure if I was on to something useful or not.


I've read a tutorial by Wes Macaulay that instructed to import the CAD file and acquire its coordinate system within Revit using the Shared Site (Record current position as..). I did this but everything got screwed up. The exported CAD files were fine but the real North got lost in Revit and the Revit files fully lost its old coordinates. The other Revit linked files could no longer read the correct coordinates of the Revit file and they no longer aligned.

Please let me know if you can assist me and if you require any additional information. Thank you in advance.

[MikeJarosz]

Shared coordinates have been one of the more difficult Revit concepts for new users to master. There have been lots and lots of complaints. I once attended a Revit User group meeting where an experienced Civil Engineer took us through the ins and outs of shared coordinates. I walked out thinking I had finally mastered it. It does have its defenders, but this lecturer had ideas for improvements.

I sometimes think the Acad coordinate system was better. Then I remind myself that the Acad system gets unbelievably messy when you want to work in 3D. It seems that ACAD, instead of using plain vanilla cartesean coordinates, decided to make the z axis a vector. This throws it into linear algebra territory. You now need to learn vector arithmetic like cross products and dot products.

So, in the end I don't think either is very easy.

[Craig_L]

I suggest also that you have them turn the survey point ON when exporting, this will give you a solid point to work from with actual relevant co-ordinates based on the survey information. Assuming they have set this up properly to begin with...If they have project co-ordinates in there, then I suggest to you that this should already be correct, but something worth checking..turn this bad boy on (under visibility graphics - survey - survey point)

[Teresa.Martin]

We are consultants using CAD and working with architects and structural engineers using Revit.

We purchased Revit half way through the project and decided that we would stay in CAD for this project. We do use Revit to create 3d details and explore the building but all of our plans are in CAD.

The architects send us up to date CAD plans from Revit every few months.


Here is my problem. We've been working in this manner for over a year and the CAD plans they are sending us are sometimes move. Since they are xrefs, we just align them but we want to find the best practice to this so that there is no movement. We could eventually be the ones giving these types of files to other consultants so we want to know what the logical way to do this is.

The architects are all new to Revit. I have more experience, but not in this domain (coordinates and CAD collaboration. They will not be able to solve this issue, but I can troubleshoot it within their Revit files and give them the solution (given that I find it).


Right now they are exporting Sheets to DWG using Internal Project coordinates.

I know that they should be exporting Views using the Shared coordinate system. When I tried this, all the CAD drawings came in slanted to the true North. I am not sure if I was on to something useful or not.


I've read a tutorial by Wes Macaulay that instructed to import the CAD file and acquire its coordinate system within Revit using the Shared Site (Record current position as..). I did this but everything got screwed up. The exported CAD files were fine but the real North got lost in Revit and the Revit files fully lost its old coordinates. The other Revit linked files could no longer read the correct coordinates of the Revit file and they no longer aligned.

Please let me know if you can assist me and if you require any additional information. Thank you in advance.


In short, by acquiring the coordinates from the CAD file, you essentially moved/changed the coordinates in the Revit file. Since you acquired the coordinates from the CAD to the Architectural file you would then need to Publish these coordinates back to the linked Revit files so they would all be sharing the same coordinate. That is why they are way out of alignment.

Turn on the Project Base Point and the Survey Point. The Project Base Point denotes the ICS (internal coordinate system) in Revit. This is the origin of the Revit model. In Autocad this would be the WCS. However, unlike Autocad, the coordinates of the WCS do not have to be 0,0,0. They can be any number along the x,y and z.
The Project Base Point icon (blue circle with an x in the middle) denotes the project start up location in Revit. As long is this point has not been moved by unclipping it and dragging it, it will mark the origin in Revit. When you export to CAD using Project Internal Coordinates, this circle with the x will fall on the WCS origin in Autocad.

Shared coordinates, as previously mentioned, use the triangle survey point coming into Autocad as a reference.

I hope this helps!

[SamuelAB]

I suggest also that you have them turn the survey point ON when exporting, this will give you a solid point to work from with actual relevant co-ordinates based on the survey information. Assuming they have set this up properly to begin with...If they have project co-ordinates in there, then I suggest to you that this should already be correct, but something worth checking..turn this bad boy on (under visibility graphics - survey - survey point)
Their project Base point seems to be the 0,0,0 point in their CAD exports when they use Internal Project Coordinates. This seems random, because it changes. Seems like a good enough reason to move away from internal project coordinates.

Unfortunately, I won't be able to have them show the Project Base point or Survey point since they won't want it to show on the construction plans. As well, I believe it would only show up on the first floor plan if it falls within the view range.

[MikeJarosz]

Revit and ACAD are polar opposites regarding coordinates. In Acad, the default UCS has 0 0 0 as the origin and you move the building around on the map. In Revit the building stays put and you move the map around. A lot of people find the Revit approach hard to grasp.

[SamuelAB]

The Project Base Point icon (blue circle with an x in the middle) denotes the project start up location in Revit. As long is this point has not been moved by unclipping it and dragging it, it will mark the origin in Revit.

When you export to CAD using Project Internal Coordinates, this circle with the x will fall on the WCS origin in Autocad.

Shared coordinates, as previously mentioned, use the triangle survey point coming into Autocad as a reference.

I hope this helps!

So CAD drawing exported using the Shared coordinates will use the Survey point as 0,0,0. As mentioned before, exporting using Shared Coordinates produces a CAD drawings that is rotated to true north.

The solution so far seems to be:
Export every view using Shared Coordinates, rotate them within AutoCAD.

I will play around and see if any problems arise.

[SamuelAB]

It kind of makes sense. In CAD it's somewhat easy to just grab everything an move it (assuming you did not leave any layers locked or frozen).

In Revit, it is seemingly impossible to grab everything and move it since the annotations can only be modified within the view and cannot be dragged from the 3d view.


I remember when Collaboration concepts seemed very muddy. Now they seem very simple and even childish. I hope the same happens with these Coordinate Systems.

[MikeJarosz]

In Revit, it is seemingly impossible to grab everything and move it since the annotations can only be modified within the view and cannot be dragged from the 3d view.

Brilliant Observation!!!

Of course, now it makes sense. It would be a nightmare to move everything around in Revit when so much data is view dependent. The solution? Don't move the wine glasses, move the tablecloth.

[SamuelAB]

I've come up with a resolution.

We asked that they lock their Project Base point and send the CAD files as View instead of Sheets while using the Internal Coordinate system.

I am still unsure as to why the 0,0,0 on some drawings (not all) was moving randomly in CAD, but this will hopefully resolve the issue. I am guessing it may have been associated with the fact that Sheets were exported.

If you have any insight as to why it was moving, please let me know.

[MikeJarosz]

I am still unsure as to why the 0,0,0 on some drawings (not all) was moving randomly in CAD

In CAD, it's an old joke that the origin was wherever the crosshairs were when you started the drawing.

Nowadays, with energy analysis, ecotect, navisworks, real shadow studies etc., a building has to be oriented correctly. The CAD old guard is going to have to learn this.

[Ning Zhou]

Revit and ACAD are polar opposites regarding coordinates. In Acad, the default UCS has 0 0 0 as the origin and you move the building around on the map. In Revit the building stays put and you move the map around. A lot of people find the Revit approach hard to grasp.

that's it! as simple as this plain English, i wish i can realize this much much much ... early.


It would be a nightmare to move everything around in Revit when so much data is view dependent. The solution? Don't move the wine glasses, move the tablecloth.

again, i kept wondering why Revit cannot use ACAD coordinates system for very very very ... long time.

[MikeJarosz]

AHA!!!

I think Ning had one of those Revit moments when the lightbulb went on and suddenly it all makes sense!

[gtarch]

I have a question:

Is manually moving the project base point the same thing as using the relocate project tool?

[silexz]

One thing I have noticed while exporting sheets to .dwg is that Revit will use the Internal Coordinates of the FIRST view placed on the sheet.

Sometimes I put a legend onto a floor plan sheet first...then Revit uses that legend view's coordinates for the Origin in ACAD instead of my main plan...hence the change in origins.

For sheets with multiple views on them, Revit gives priority to the first view placed on that sheet when determining which 0,0 to export.

[silexz]

Also a follow-up.

There is an invisible origin in Revit that is not the same thing as the Project Base Point / Survey Point.

You can see where it is by importing a .dwg Origin to Origin with some lines in it that intersect in the .dwg's own Origin aka 0,0.

For whatever reason 0,0 in ACAD is not the same as the 0,0 we create via our Project Base Point in Revit. It's driving me nuts as we speak.

[patricks]

One thing I have noticed while exporting sheets to .dwg is that Revit will use the Internal Coordinates of the FIRST view placed on the sheet.

Sometimes I put a legend onto a floor plan sheet first...then Revit uses that legend view's coordinates for the Origin in ACAD instead of my main plan...hence the change in origins.

For sheets with multiple views on them, Revit gives priority to the first view placed on that sheet when determining which 0,0 to export.

What you're describing is exactly why nobody should ever export SHEETS when sending CAD exports for collaboration to consultants. Views are the only thing that should ever be exported for collaboration.

[silexz]

Unfortunately sheets have the title block, which has some important legal jargon, logos, copyright and issue block information which is important for coordination.

Exporting sheets can be done, you just need the foresight to place the right view first. The other option is to relocate the base point in CAD afterwards. But who wants to do extra work??

[breckbaird]

One technique I have used in the past (for large projects) is to export a model view showing the entire level and export the sheets showing the partial floor plans. Then in AutoCAD I would delete the partial floor plan in model space and replace it with an Xref to the exported DWG of the entire floor. Then the consultants would get one floor plan (for each level) to do their work on as well as the sheets with the necessary legal jargon on it.

There are a few drawback to this method which resulted in some ugly looking drawings when the consultants didn’t take the time to clean up things like matchlines and grid bubbles, but at least the information was accurate and the DWG files always had the same coordinates.