Revit to CAD Export Precision

[cslaten]

My team has recently encountered an issue where all Revit drawings exported to AutoCAD default to 1/16" precision when the units are viewed in CAD.  My understanding is that this is easily remedied by changing the units to 1/256" after export, but people are fallible and forget to make the change before they start working.

I've read on other forums that the scale of the drawing being exported from Revit influences the unit precision settings of the CAD file, but I've tested this and determined it false.  The default is always 1/16".  Is there a way to change this?  My native AutoCAD unit default is 1/256" so that's not the issue here either.  

I'm beginning to think that this is a baked in Revit / AutoCAD oversight, but hopefully someone out there has figured out how to change the default.

Thanks!

[ToanDN]

Were the elements drawn with smaller than 1/16" precision? If you draw a wall as 10'-10 1/32" long in Revit, what will it become in CAD?

[barthbradley]

Change the precision through DDUNITS in AutoCAD.

[cslaten]

It is still drawn at 10'-10 1/32", however, if you were to measure this distance in the CAD file w/out changing the default units, it measures as 10' - 10 1/16".  It's really only an issue if you have people in the office creating CAD details from your exported Revit drawings.  Unfortunately, that's the case at my firm, at least for the near future.  

[barthbradley]

What's the precision of your AutoCAD units? 1/16th? 

[cslaten]

Yes, this works.  However,  my issue is that you have to do this with every exported CAD file prior to beginning work, and people inevitably will forget to change the units.

My issue is that I would like the default to be 1/256" when exporting to CAD, so that team members do not need to think about going and changing the precision when they get a CAD export from our Revit project.  As mentioned previously, our default new CAD file is already set to 1/256" precision.

[Anonymous]

Revit exports were never intended for being used for production use/editability.  They are more for reference.  1/16" tolerance is the default for OOTB Autocad, so my guess is that it was hardcoded that way for export.

If your template is configured for 1/256" tolerance for units and dimstyles, I would suggest Xref the Revit Export and then bind/explode if you are going to make changes.

Personally...if you are exporting from Revit to CAD for production use, you are better off creating everything in Autocad as Revit exports are terrible when it comes to manipulation.

[cslaten]

Correct, the default precision in the CAD file is 1/16" and you have to manually go and change it when you receive a new export from Revit.

[cslaten]

Yes,  this is what I was thinking as well, although it's just as easy to simply change the precision at that point.  Personally, I would never take things back into CAD from Revit, and always advise against it, but some of our staff only operate in CAD.  

[RobDraw]

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@cslaten wrote:

My team has recently encountered an issue where all Revit drawings exported to AutoCAD default to 1/16" precision when the units are viewed in CAD.  My understanding is that this is easily remedied by changing the units to 1/256" after export, but people are fallible and forget to make the change before they start working.

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Yeah, no one is perfect but they should remember at some point. One would think this is settable during export somehow. Revit has to be using a template of some sort. Where it is, though...

[barthbradley]

Okay, I'm a little confused. If your DDUNITS are set to 1/256" precision, then 1/256" precision will report for a Revit elements, if they are in fact that precise.  But you are saying they are not?  

[RobDraw]

@barthbradley units precision only affects the result when measuring and dimensioning. Changing the precision does not affect the actual length, only the rounding. The issue here is the initial units setting being 1/16" and no way to set it before exporting.

[Anonymous]

This could be a good Revit Idea suggestion to allow for DWG default tolerance exports to be configured in the Revit.ini.

[cslaten]

Bingo

[barthbradley]

Thanks @RobDraw. I understand precision, but what I'm trying to wrap my brain around, is what the correlation is between precision and exporting.  Precision doesn't effect the actual size.   See where my confusion is?  

[cslaten]

Yes, I'll add it.  I think that it should be as simple as adding this as an option to the Units & Coordinates tab on the export options dialogue.

How many votes do you need for Autodesk to consider something?  Most of my ideas get a up votes but nothing that generates enough buzz to be considered....

[RobDraw]

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@barthbradley wrote:

Thanks @RobDraw. I understand precision, but what I'm trying to wrap my brain around, is what the correlation is between precision and exporting.  Precision doesn't effect the actual size.   See where my confusion is?  

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If a user does not change the units precision in the .dwg, then measurements might not be accurate for detailing.

[RobDraw]

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@cslaten wrote:

How many votes do you need for Autodesk to consider something?  Most of my ideas get a up votes but nothing that generates enough buzz to be considered....

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It's not just votes. Somethings are just not possible and will never be implemented even though people say it should be an easy fix. That's why the ideas forum is a joke, IMVHO. 

[cslaten]

@barthbradley you are correct.  It doesn't.  However, when someone begins working on an exported drawing, not knowing that the units have been set to 1/16" and use the measuring tool, they aren't going to know that the dimensions that they are getting back are slightly off.

Now, ideally my Revit team isn't building things to anything less that 1/16" tolerance, but we are a classical firm that deals with very small ornate details.  The various steps in our profiles can sometimes be smaller than 1/16". We actually hold our builders to this (and our clients pay a premium for our eye on such detail).

Part of my job as BIM Director is to try and eliminate these little hiccups that can trip people up in our work flow, and try to make things as fool proof as possible.

[barthbradley]

Ah! So the idea is that it opens in AutoCAD at the correct precision! Got it! Thanks for sticking with me on this one, @RobDraw.  

..p.s. I'll vote on the IDEA @cslaten. Link us to it when it's up and running.