Forums >> Revit Building >> Technical Support >> Why does my Imported .dwg dance???

JRPcad

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Hi All,

I'm working on quite a big project where i'm having to create a large block of buildings as an existing Revit Model.

I've finally got to the roofs and have inserted a dwg. of the existing roof plan survey data. for some reason though as I zoom in and out of the plan, the lines dance!!! ie. I know that i have inserted it to land directly on a wall line, at first it looks fine but as i zoom into that wall you can see the lines of the dwg. darting around effectively looking like they are slightly changing position and orientation, it always seems close but never exactly on the lines.

I've got my survey guy to copy it to a completely new file aswell as drawing on a file that i know works perfectly, but still the same problem. can anyone shed any light on why this is happening please?

Thanks in Advance

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WWHub

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Probably the inaccuracies of CAD.  Believe it or not! 

CAD treats each end of line elements as points with their own location defined to XXX decimal places (I don't remember how many).  As such, the lines may look parallel or at the correct angle and will measure correctly in CAD but Revit uses something different.  Not sure exactly how it works but this is why Revit does not like very small measurements.

This is why you can have two apparent parallel lines in CAD that when imported into Revit, you can't place a dimension between them because Revit does not see them as parallel.

I always encourage people that use CAD imports to be very cautious.  Don't just "pick" the CAD lines or if you explode CAD, always check the lines for angle accuracy according to Revit's rules.

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JRPcad

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I'm not sure that is the case, as I have a fair few other drawings in that seem to be fine (no movement at all, when i zoom in the lines stay where they should be)

As it's existing survey data the proper way for me to do this would surely be to pick the lines as i need the revit model to match the survey data, and as I say it's worked perfect so far this has only occured since i've tried to bring in the roof plan.

I've even tested it by removing my original site plan .dwg which i originally used to trace the lines which worked fine originally. However when I try and bring that back in it has the same issues as the roofplan does even though it worked fine before.

This is why i'm assuming the problem lies witin revit somewhere, maybe a setting i need to change??? the problem wasn't around yesterday but is today and it seems like it isn't going to go away.

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JRPcad

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Okay while writing these posts i've sussed what is wrong (well found a work around lol):

It appears there is a fairly major fault with Revit 2012 that maybe needs to be worked out by the Devs fairly quickly, as this could be causing alot of errors in alot of peoples models.

I've found that I was bringing the model in using "Manual Center" this for some reason was causing the lines to dance and move around (only slightly, but still!) when i import using "origin to origin" there is no issue at all, the dwg. works perfectly in Revit.

Hence Can I suggest that if any of you are using "manual Center" when insering/linking, you check and double check your models as they are very likely slightly wrong lol!!!!

As a quick follow up to this, I've just had a quick check of some walls I drawn while the DWG lines were dancing, turns out they ended up 40mm away from where they should have been. quite alot really when you consider a standard wall width.

Edited on: Thu, Sep 15, 2011 at 9:04:05 AM

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scrounger

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I was having the same issue using 2012 and linking/importing via manual origin. Re-importing using 'origin to origin' did not fix my problem, but exploding the CAD file, running a purge and then re-importing did. 

I hope Autodesk can patch this up in 2013. 

-Scrng

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sllana

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Well, I can tell you, Autodesk could not fix that issue in 2013, I cuold fix it exploding the cad file in revit 2012, but now in 2013 couldnt fix it at all doing the same.

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JRPcad

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I've not had the issue yet in 2013,

I found that problems occured due to locked layers also, my advice would be to copy paste all of the information you require to a new file, ensure that all layers you require are on, thawed and unlocked. If you have any blocks within the CAD file explode them and ensure that everything is flat (as it is a 2D drawing), I was finding that varying z values within a 2D CAD import were also causing a lot of issues. Purge and audit the file.

To put basically clean the drawing up, Revit expects a CAD import to be drawn correctly, any messiness in there can throw Revit off track in one way or another.

The situation has deffinately improved a lot in the recent releases though as I'm finding I can rely on the imports more and more without having to go through my cleaning procedures

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WWHub

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I think a lot of these problems occur with a CAD file that has its origin at a large distance away.  Opening the CAD file and wblocking with a closer origin has always seemed to help.

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sllana

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I can add: it is very important to check the orthogonality of the drawing. Some times they are rotated 0.000001 degree or something like that and that makes revit going crazy.

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MirkoJurcevic

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I had similar problem while inserting dwg into Revit. DWG was 'dancing' in the floorplan, it was all messed up.

Problem was that Revit had shared coordinates system that matched the one from dwg (coordinates around 5.000.000 meters E/W and N/S).

While separating parts of dwg file, I discovered that the problem is in AutoCAD blocks that are too far away from the WCS zero (as they should be, because the whole drawing is geocoded).

After exploding the blocks, Purging, Auditing, -PU Regapps, PU and AUdit again, everything works fine.

Before that, I tried every advice from this thread. None was helpful.

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portedaix

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In 2017 the problem is still there. Further to dancing lines, I had filled in volumes becoming huge. I followed all the advices there, problem solved ! Thanks.

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mauriciom3

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Hello!

I have the same problem and then i notice that the CAD that i was importing becomes like a block, so I just "exploded" and then I reload the CAD file the "voila" works.

Regards,

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