Forums >> Revit Building >> Technical Support >> AutoCad Units Inaccuracy

JDAGEN

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Joined: Fri, Apr 17, 2009
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I am working on our first firms Revit Project. Our designers who do not know Revit have been working on a floor plan in AutoCad which is linked into the Revit model. As they make plans to the Cad file we update the Revit model. One thing we have noticed is that the AutoCad plan is notoiuosly off in several areas by incriments of /256". I have worked in Autocad for years and never seen anything like this. Has AutoCad always been this inaccuate? Is this a known issue between AutoCad and Revit or is it user error? Should linking Cad plans this way be avoide?

Thankyou in advance.

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WWHub

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Joined: Tue, May 16, 2006
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Revit only handles units to 1/256".  As a consequence, some AutoCAD drawings may be rounded.  But, overall, we find that most AutoCAD drawings are bad because they are drawn to units different than how they are dimensioned. We don't like to import CAD drawings unless we clean them up first.

I really like the fact that REVIT doesn't draw anything smaller than 1/256 and I really like that you can't over-ride a dimension.

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JDAGEN

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Joined: Fri, Apr 17, 2009
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Do you round project units or dimension units in evit, or do you draw everything to /256"? I am still trying to understand if Autocad is that inaccurate or if it is user error. It appears AutoCad rounds and approximates so that when an osnap appears to be to a point on a line it is actually off be hundreths of an inch, even if units are set to 1/16". It also apears that the same is true with typing in dimensions. I didn't create the original cad plan, but it looks like someone would have to try to mess it up this badly.

Thanks for your help.

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mrmoo

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Joined: Thu, Sep 13, 2007
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its not that AutoCAD is inaccurate, its that its too accurate for its own good.  check to see that your cad drawing's dimensions are truly accurate (i think thats where WWHub is going).  it is very easy to fake-out autocad; you really can't do that with revit.

 though i will say that it would be nice to be able to enter numbers into dimensions - not to override the dimension - but to treat it as text; say with quantities.

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