Forums >> General Discussion >> Revit Project Management >> export revit model with exact measurements

methynn

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Joined: Sat, Aug 17, 2013
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Hi,

I have a question about exporting revit models. When I try to export models in 2d dwg everything works fine.

All dimensions are exactly the same when opened in sketch up. But the measurements on the exported 3d model is

changed. For example a 600cm wall dimension is like 599.98856 etc. I am trying to open the revit model in sketch up.

Any ideas?

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WWHub

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Joined: Tue, May 16, 2006
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The problem may be the way you created the model.  If you 'sketched' all items rather than placing them by dimension, then you may have some built in errors that don't show up in Revit's dimensions.   Try clicking on the wall you used in your example and in the highlighted (blue) 600cm dimension type in "600.0" to set it exactly at 600.  Now see what happens.

We have seen that todays computer savy users don't understand the importance of being exact when they model. 

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methynn

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Thenks for the reply. I tried your method but still the same. I ve discovered that  when export in .ifc

some of the problems are gone. Thickness of a 150mm generic floor is 150.000001.

I think its about conversion algorithms. Cant find a solution. By the way I am exporting as .dwg 2004

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MichaelJarosz

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There is a difference between dimensioning and measuring. Measuring with the Revit ruler gives an exact number. An exact number in Revit is an entire discussion by itself. A dimension is a ROUNDED number. Do this: make an dimension style named EXACT. Set the primary units to inches and the rounding to custom .0001. That is about as exact as any building measurement will ever be. Then set the alternate units to your usual dimensioning standards, like feet and fractional inches with 1/8" rounding. Now, change your dimension styles to the new exact dimension style. If you see a primary dimension like 60.003 and an alternate as 5'-0" you will see where the inaccuraces in your model are. Most people forget that dimensions are rounded. If it says 5'-0", then it must be. right? But it ain't neccessarily so! Also when working with a clumsy system like feet and inches, what kind of number is 10'-3 7/8" divided into 5 equal parts?

The next issue most users have a hard time with, but the fact is most computers cannot do exact precision computations. They use what is called floating point numbers, which are inherently inexact. That's how you get numbers like 15.0000001. If you are interested, Google "floating point representation of numbers". Then of course, none of the computations are done in base 10 anyway, so there are some surprises in binary computation and the conversion of binary to decimal to feet and inches.

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