Export to Acad hard to clean up

[Andre Baros]

I needed to go back and work on a legacy Acad Project... to create new millwork elevations to drop into existing interior elevations, so I drew the new material in Revit (because it's just faster) and exported out to AutoCAD. We do this all the time for consultants to use as backgrounds, but this was the first time that I had to work with the data in AutoCAD and the problem I found was that I had a LOT of lines on top of each other. Each time I tried to trim something I was clicking a dozen times. The exported file also had a lot of lines sitting end to end.

The usual solution (since we get these all the time from certain consultants) is to run overkill. But overkill didn't work on the Revit entities. What makes them different from native AutoCAD entities to prevent easy cleanup (or better yet, why can't they export cleanly)?

PS. Plans seam to clean up better than elevations or families (families are the biggest offenders).

Thanks,

[mlgatzke]

This is a known "problem" with dwg exports from Revit. The guys at WATG have been fighting with this for quite a while and they are working with Autodesk to find an amicable solution.

As far as why the Revit objects are handled differently from the genuine AutoCAD objects, I'm afraid I don't know. Revit may export the objects with specific object handles that AutoCAD has problems running "overkill" with. I'm sorry I can't help you there.

[Wes Macaulay]

I'm not sure how the problem materializes since some exports to Acad work great - only two lines per wall - no stacked lines, and then other times you get several lines stacked one on another. Might have something to do with multiple wall objects (vertically) visible within the view range... never experimented to see why the problem arises.

[MikeJarosz]

Think in 3D. If you look at a simple 3 dimensional cube in elevation, the top of the cube is actually two lines - the front edge and the back edge. Exporting this elevation view only "smashes" the two lines on top of each other.

One terrible shortcoming of Autocad is its almost complete lack of cleanup utilities. You have discovered overkill, which I believe is actually an add-in, not an intrinsic Acad command. It finds what it can, which, as you have found, is less than perfect. Try running it more than once. Make sure the lines all have the same properties.

What is needed is a utility that can rigorously find multiple coplanar and collinear entities. Maybe one day Autodesk will wake up on this one.

Another trick comes to mind, but I have never tried this technique in Autocad, although it works great in another CAD system I know. A little known feature of Acad it its ability to read a plot file back in as data. Try plotting your ACAD translation to a plot file and read it back in. I'd be curious what you get.

One other thing you can try is hidden line removal (in ACAD). Plot with hidden line removal on, then load back the file and see what happened.

[Andre Baros]

I understand the 3d lines to 2d lines concept, and Revit seams to understand it for basic elements, ie. walls, floors, roofs, but seams to forget it for curtain walls, families, etc. It cleans some stuff up and not others.

Overkill was is built in since Acad2002 or Acad2004 I think, and it goes a long way to solving the problem most of the time. But for some reason it seams to miss some of the Revit entities, again, no problem cleaning up some items and completely ignoring others items.

[DanielleAnderson]

We have had these same kinds of issues with exports and find it just a lot of tedious acad work in the export. I am just curious if anybody has tried to use LSP routines to clean these things up and if so, what has been successful?

[tatlin]

Think in 3D. If you look at a simple 3 dimensional cube in elevation, the top of the cube is actually two lines - the front edge and the back edge. Exporting this elevation view only "smashes" the two lines on top of each other.
This is not quite what happens. Export is smart enough to handle 'simple' cases like this while projecting the 3d model to a 2d plane.

There are some more complicated issues that still need to be dealt with, of course. For these cases, it helps to have specific examples (like the ones from WATG) pointed out and prioritized, so we can work more efficently on getting them fixed.

[MikeJarosz]

Thanks for the correction, Vladimir