Should Revit align its coordinate system with AutoCAD WCS 0,0?

[Wes Macaulay]

Per the thread with regards to Revit and how it creates the coordinate system in the exported DWGs, consider the following, and vote on the issue.

Nasty but necessary long preamble
Most major design firms pick a location in their project which will be the "project origin". Generally, this point is set to be 0,0 in the AutoCAD World Coordinate System.

When one discipline wants to overlay another's work, they can xref the other consultant's work in, insert at 0,0 and know that the work is perfectly overlaid -- no need to insert then move to align grid intersections in the base drawing and the xref.

But here's what happens in Revit: you import data at (say, a circle with center at 0,0) from AutoCAD. Here's the options and what happens. In each case the Link option is selected so we can write back to the DWG if needed.

1 Import DWG Origin-to-origin: the imported circle at WCS 0,0 lands more or less at the centre of the Revit drawing area at Revit's origin. Now use the Report Shared Coordinates tool and snap the the center of the circle -- it will report 0,0. But let's say we don't want this location to be the project origin - we have a grid intersection at another location in our Revit model which we want to be the project origin.

So you use the Relocate this Project tool and move the project from the grid intersection to the center of the circle -- you're essentially telling Revit that you want the Revit coordinate system moved so that the grid intersection is now at 0,0.

Everything moves, including the imported circle. Now use the Report Shared Coordinates tool again, and click the grid intersection -- Revit tells you this is now 0,0.

So you'd expect that if you exported to DWG now, the grid intersection would become 0,0 in the WCS of the exported DWG. It's not -- it's still at the center of the circle.

On to another option...

2 Import DWG using Shared Coordinates: using the same circle, import it as a Link using Share Coordinates. Revit will tell you that the files don't share coordinates, and it will align the DWGs world coordinates with the Revit coordinate system. The circle lands in the same place.

Now relocate the project from the grid intersection to the center of the circle. This time the circle does not move, and the grid intersection is now aligned with the center of the circle. Revit's coordinate system reports that 0,0 is the center of the circle / grid intersection.

Right click on the circle and go to Properties and click the Shared Location button. Choose to Record the location as the 'Default Location' which will modify the linked file.

Go to Manage Links under the File menu and click on the DWG containing the circle, and then click Save Locations. Choose to Save the coordinate system back to the DWG. Open the DWG with the circle in it and note that the Revit-created UCS and WCS are the same... 0,0 is in the same place. Which makes sense. But...

Export to AutoCAD, and 0,0 is now where the circle used to be, not where it is now! Again, this is not what you would expect or want.

So how important is it that Revit write DWGs where the origin of the Revit coordinate system becomes 0,0 in the AutoCAD WCS in the DWGs it exports?

[hand471037]

Another thing to think about is an issue that just came up with a local firm that's looking at using Revit on a large transit project. They want to bring into Revit DWG files that are *miles* wide. This raises issues with the 0,0 and with the fact that Revit seems to have some issues in dealing with such 'wide' DWG's (it always wants to center them upon import for some reason).

So it's not just the 0,0 coordination between Revit and AutoCAD, there's also the issue of 'cropping' the DWG upon import into Revit to just be the bit you need, while still having the rest of the DWG available.

[Wes Macaulay]

Ditto on the large coordinates -- we had that same problem on a large project in Washington. I don't know if the new build fixes that...

[MikeJarosz]

Ditto Freedom Tower. The project surveyors are using NAD83 coordinates with a datum point 189 miles to the southwest, and the building is not orthagonal to this grid. This generates enormous coordinate numbers at our site. Also, an error of one second of rotation about the datum point subtends an arc over four feet at the site.

Since most of the world continues to use ACAD, we MUST have the ability to export a correctly located plan in DWG format, so that consultants can overlay our backgrounds accurately. The good news is: we have discovered that the error in exporting to DWG is consistent, so we wrote a lisp routine to move the exported files to the correct location (in ACAD).

But there has to be a better way...

[mnielsen]

I can second what Wes has said, for he helped us with that same project.
This was a very big issue, and it was very difficult to find this out at the stage of the project we were in, let alone the fact that we convinced the client that the information we created in Revit could be transferred to ACAD seamlessly for the Engineers to use. Regardless, we were able to create a work-around, and show the client that this is a good program for what we were producing.

In all projects, it's imperative for the Architect's files to be able to transfer seamlessly between the programs and information that the other design team members are using. Therefore, the answer to the question regarding whether it is best to export to the WCS or a UCS seems obvious. The implied origin in both programs need to be the same at the primary level - and that is (sorry for using the ACAD term here) the World Coordinate System.

Thank you Wes for posting these threads! ...This is something that has been a big issue for me to deal with in the past year.

[DanielleAnderson]

Amen Mark!

[Wes Macaulay]

The good news is that this should not be hard to fix. The bad news is that it took me this long to test the myriad different ways of dealing with shared coordinates and exporting and importing to and from AutoCAD! :Oops:

[BillyGrey]

On this issue, the WCS does seem to this toddler to be a simple solution to a complex problem.

[Wes Macaulay]

Fedor did post a workaround (thanks, Fedor): if you link in the freshly exported DWG using shared coordinates, and then line up the DWG with your model and save the coordinates back into the DWG, you get a new UCS in the DWG called "REVIT60-DefaultLocation" (shouldn't it say "REVIT61..." guys? :wink: )

The 0,0 in this UCS does in fact align with 0,0 in the Revit coordinate system.

Of course, all your plan drawings have to use this UCS -- yours, and all of your consultants! I have done this before on some crazy AutoCAD projects.

[Wes Macaulay]

It's interesting to see the voting in this thread -- how common is it for people to set up WCS 0,0 as THE reference point in their project in AutoCAD? Given the various drafting styles I see locally, it would be interesting to see how AutoCAD usage and practices might differ across geographical regions.

[bclarch]

Wes,

One of the things that makes this interesting is that this is one of those issues that is very important to those who need it and of no importance at all to those who don't. We do mostly residential work with some light commercial and occassional small office build-outs. We don't use the WCS at all. On the occassions where we do need to coordinate with outside consultants it is easy enough to align things manually. However, I certainly understand the need for automatic and precise alignment of consultant's drawings in large scale projects. Lack of coordination can cause a myriad of problems and manual alignment is a great time waster on large projects.

As a result of considering both sides of the issue, I have not voted in the poll because I am uncertain as to what sort of input the Factory needs on this issue. If they want a true snapshot of how individual firms actually work then I should vote no. If they want to know about issues that we recognize as potential problems, even if they are not an issue to our firm at the moment, then I should vote yes. Interesting indeed.

[UKITManager]

In England, we use the WCS based off our original survey information (a national OS grid reference system) we typically setup the "site plan drawings" off this survey then create numerous UCS to allow for orthographic projection etc. All of our drawings including the elevations are set to 0,0,0 as a datum and we need Revit to accommodate this "round trip" one trick we have used whilst importing is to place a dot at the WCS before linking the drawing into Revit and it can land with the 0,0,0 in the ACAD WCS. Our problem is then getting Revit to Export out the same orientation.

I would also add that Revit needs the ability to tick a box and export dwgs as bound dwgs and not xrefs. May be use a pull down box with either or as a default export method.

[FK]

About that workaround - I don't like that "line up" step during export - I suggested you link origin-to-origin. This way the exported model coincides with the original model. The entire sequence is:

Project setup:

1. Link or import (origin-to-origin) a dwg file that clearly identifies your point of reference (say, a crosshair at the WCS origin).

2. Move/rotate the crosshair into position in the Revit model.

3. Acquire coordinates from the file.

(4. Get rid of the link.)

Export:

1. Export file.

2. Link it back origin-to-origin.

3. Publish coordinates into the file.

(4. Get rid of the link.)

Thus, the WCS of the original file becomes the "REVIT60-DefaultLocation" UCS of the new file. Also, you align files only once, so export is faster and less error-prone.

If you really want to live on the edge, you can try to batch the whole export process with a journal file, but keep in mind that it's totally unsupported. Basically, the sequence "open file, export, agree to overwrite, link, publish, save link, exit, don't save project with unwanted link" should replay reliably, producing updated versions of the exported file (as long as it's not confused about which file is where - you may have to edit the journal). This could be a method to automatically regenerate dwgs from the model. Don't forget that you train unsupported functionality at valuable project files at your own risk and if something goes wrong it's not our fault.

Revit development is aware of the requests to improve this functionality, but does not commit to any specific dates or plans.

[Wes Macaulay]

What I'm planing to tell people to do is have the new UCS Revit creates in the linked DWG used as a block by AutoCAD users. When you insert this block into a drawing, the UCS definition comes with it. As long as that UCS is set current, everything will line up fine.


If they want a true snapshot of how individual firms actually work then I should vote no. If they want to know about issues that we recognize as potential problems, even if they are not an issue to our firm at the moment, then I should vote yes. Interesting indeed.I suppose I would tell people to look ahead and determine if they will ever need to work with the AutoCAD WCS; in most cases I would assume yes. But if you have never used it for years' worth of work, I guess it's safe to say you probably won't need it in the future.

And when it comes to creating data, we are all certainly at our own risk -- no matter what app we use! I sometimes have a brief panic attack when I think of all that intangible digital data out there, just waiting to blow up.

[sbrown]

FK, Thanks for your help on this.

I just want to understand the process here, so please verify below that I'm understanding your post.

Project setup:

1. Link or import (origin-to-origin) a dwg file that clearly identifies your point of reference (say, a crosshair at the WCS origin).

2. Move/rotate the crosshair into position in the Revit model.

(does it matter if the model has been rotated to true north?, Should the model not have been rotated.

3. Acquire coordinates from the file.

(4. Get rid of the link.)

Export:

1. Export file.

The plan? should it be project north or true north?

2. Link it back origin-to-origin.

I assume the exported revit plan.

3. Publish coordinates into the file.

Publish into the exported revit dwg plan?

(4. Get rid of the link.)

[FK]

2. Move/rotate the crosshair into position in the Revit model.

(does it matter if the model has been rotated to true north?, Should the model not have been rotated.
Actually, the existing shared coordinates that the file has do not matter at all - they'll get clobbered. Once you acquire coordinates from the dwg, its position and orientation will specify where shared origin and true north are. Probably there will be less chance of confusion if you display your plan oriented to project north.


1. Export file.

The plan? should it be project north or true north?
Well, export what you need to export from the model - perhaps a plan view. I think project north should work fine, and true north may or may not get rotated twice - not sure.


2. Link it back origin-to-origin.

I assume the exported revit plan.
Yep.


3. Publish coordinates into the file.

Publish into the exported revit dwg plan?

Yep. And make sure it gets saved (File->Manage Links->Save Locations, Remove).

[jwilhelm]

Lets stop making Revit "Like" Autocad, I personally chose Revit because Autocad sucks, lets not compromise Autocad to accomodate the use of autocad files in Revit, if your gonna use Autocad, use Autocad.

[mmulvey]

I wouldn't go so far as to say AutoCAD "sucks" - it's success over the years is proof that it has met most people's needs adequately.

Even if it is not perfect - admittedly, its far from it - we should not be too proud to take ACAD parts, procedures, ideas and incorporate them into Revit where appropriate to build a better product that will benefit all of us.

The original authors of Revit had good reasons to deliberately distance themselves from ACAD wherever possible. Those reasons no longer exist.

[Steve_Stafford]

Whether we like AutoCAD or not is irrelevant...it is still used by many of the people we will do projects with. You can either make the interaction pleasant or unpleasant. Even if you are very selective and demand all consultants use Revit...somewhere, sometime, someone will need a dwg file.

Improving the fundamental relationship between Revit and AutoCAD will do much to improve the reputation and perception of Revit in our industry.

[LRaiz]

I wouldn't go so far as to say AutoCAD "sucks" - it's success over the years is proof that it has met most people's needs adequately.
....
The original authors of Revit had good reasons to deliberately distance themselves from ACAD wherever possible. Those reasons no longer exist.

Original authors never tried to distance Revit from ACAD whenever possible. We realized that ACAD as a horizontal drafting tool is here to stay for a very long time and Revit never attempted to compete in pure 2d non-parametric drafting. We tried to address ACAD limitations when the tool is applied to a complex problem of building design (e.g. layers standards, annotations that are not aware of view scales, lack of view coordination, absence of dimensionally driven geometry, absence of parametric geometry, lack of element interaction and change propagation, model/paper space complexities, multiple file management, etc.). In short Revit, was focusing on different issues.

Right from the beginning we realized that we live in ACAD ecosystem and must coexist and inter-operate nicely as far as drafting is concerned. That is why starting with Release 1 we paid a lot of attention to dwg import and export. There is more room to improve in this area and the factory is aware of it.



Improving the fundamental relationship between Revit and AutoCAD will do much to improve the reputation and perception of Revit in our industry.
We agree. Furthermore, we understand that improving this relationship will do much to contribute to Revit's commercial success.

[Wes Macaulay]

Here's a PDF I created which will hopefully help everyone out with regards to this topic.

[beegee]

Very nice work Wes.

Thanks for taking to time to do that.

[FK]

That's a very nice PDF that totally ignores my new and improved process posted here. ;-) It forces you to manually align files every time you want to export.

[Wes Macaulay]

:Oops: You're right Fedor!

Here's the version using your suggestion. It's a much better solution.

[FK]

Purrr-phect! :p

While you are in that "Manage Links" dialog, you want to delete the link - you no longer need it.

[push84]

hi Wes Macaulay,
I must thank u for starting this topic, because in our firm i am starting to use revit for big project (i am using revit for last 2 yrs but not bothered abt usc until now) according to ur pdf i created circle in my site plan at ) 0,0 UCS and imported to revit with origin to origin option but my file got collapsed(see the attachment) totally because the site is located too for from centre!! (its a 6 Km township project). but with centre to centre option i am able to bring the site into revit (without circle at 0,0). i am been braking my head regarding this coordinates for past 1 week, we need this coordinates to be corrected because our other then us everyone is in still CAD platform, so they will exref our revit exported cad files. could any one help me to solve this issue! Please guys if iam not able to solve this issue, my company wont allows me to implement revit for now.

Is there any other way to work around so when I give my revit exported dwgs to others will have the same ucs as master plan has?

[pfaudler]

If the site is too far then you have to change origin in masterplan to bring near to origin and record the difference between new origin and original origin in cad protocol for that project. the whole team then work with new origin but when it comes to setting out on -site based on revit exported plans with new origin, we can xref with the difference added in x and y coordinates to get the masterplan.

Please see the recent post on this subject. "Revit 2009 prject origin"
Regards

[push84]

Hi Rahul,
i could not find the Post "Revit 2009 Project", could you please provide me the link of it?

[push84]

Please find the attachment of 2 cad files, the grid file is the original autocad file and the other one is exported cad basement file. Now The coordinate at grid intersection 1 and A is N 2613535288mm E 629102306mm.
1. How do I export my revit file to the same coordinate? Because other consultants needs with original coordinates.
2. Should we export from revit with project north or true north? My true north is rotated 17 deg, when I export my revit with true north all my annotations are not rotating as per true north. How do correct this one? When i use project north then the WCS of auto cad is different, i have to rotate and move to its location!! is this the way revit works???

Thank you
push

[pfaudler]

Hi,

Here is the Link:http://forums.augi.com/showthread.php?t=90756&highlight=Revit+2009+project+origin

In order to export your plans, you have to go to the specific plan view and export using "shared coordinate" under export option dialogue box. If you export using Revit drawing sheet then the plan will not have shared coordinate in exported DWG.

Thanks

[push84]

Hi rahul,
I have read through the project orgin revit 2009.
I imported the cad file which had site far away from its origin into revit using origin to origin option, it crumbled (see the attachment) so i tried importing using centre to center option, its coming fine into revit......now i went to tools, shared coordinates and acquired coordinates by selecting the imported cad file.......then i exported my revit file into auto cad using the shared coordinates in export options (not from sheet)and Xrefed the exported revit cad file into my original cad file (which has site for away from its origin)......but my buildings comes near the 0,0 of auto cad!!!!! With regards to this I have two issues
1. is there anything wrong in the procedure?
2. How do u manage ur files to work with coordinates? Or do u mov every time in cad after exporting from revit?

[martin.grandbois]

Hi,
From my experiences, it seems that using "Acquire coordinates" from a far away origin CAD file just doesn't work at all...

What seems to work for us is to move the Cad file so it's origin are near 0,0 origin using a line in Cad. Then we make a block of this line and keep it with our Revit files so at anytime, when exporting from Revit, we can insert the line and move the Cad back to it'S original location. Then we insert the moved Cad file into Revit and use "Acquire Coordinates" after that, the Revit project coordinates is linked with the coordinates of the moved Cad file.

[push84]

Hi,
From my experiences, it seems that using "Acquire coordinates" from a far away origin CAD file just doesn't work at all...

What seems to work for us is to move the Cad file so it's origin are near 0,0 origin using a line in Cad. Then we make a block of this line and keep it with our Revit files so at anytime, when exporting from Revit, we can insert the line and move the Cad back to it'S original location. Then we insert the moved Cad file into Revit and use "Acquire Coordinates" after that, the Revit project coordinates is linked with the coordinates of the moved Cad file.


Hi martin thank you for ur reply,
Actually i got confused in ur last sentence, correct me if i am wrong, We have to move our site in cad( which is too far from its origin) with the line and we should make that line as block file for future, then we can import this moved cad file into revit with origin to origin option and acquire coordinate from imported cad file in revit and model it revit. Once model is over export to cad then in cad with the help of the block line(which we created at the beginning) we will relocate in cad to its original location. thats it

[martin.grandbois]

Right, that what in intend to say...