Friday, August 27, 2010

Topography and BAD pads

I confess: I have not used site tools in Revit that much. There are a variety of reasons for that: not much opportunity in what I was doing in the past, insufficient tools, etc. But recently I started using them in schematic design, especially because I have made a pact with the devil to obliterate the perception that only SketchUp is adequate for this phase!

Continuing on the usual trend of reporting what doesn’t work in Revit and suggesting possible fixes, I came across a problem today. The same issue in a slightly different context has been reported over the last year by Mr. OpEd. himself, so this bug is not new.

In my case I had a sloping 8” pad for a roadway and another 1’-0” pad for a sidewalk. They share the same edges, yet the toposurface started bleeding through. What is most peculiar is that the surface of the topography itself was actually below the pads, yet it was bleeding upwards to 6” above the hosted level of the pads. This Bleeding exampleelevation turns out to be the underside of the sidewalk pad had it been perfectly flat. As a side note, the green form was built out of a sloping floor to represent grass since we cannot have overlapping pads.

 

This bug is obviously related to sloping pads. In this example, I copied and pasted the slope arrow between the two pads so they would be exactly co-planar, yet the bleeding issue still happened. After a bit of playing around with the thickness of the sidewalk pad and changing the Height Offset from Level parameter (note: I was not going for sectional accuracy here), I got the bleeding to stop. First I changed the sidewalk pad thickness to 1’-2”, then offset the pad downwards and No Bleedingthen back up to the original offset. Behavior is very inconsistent as bleeding stops after making an offset change and reverting to the previous value.

 

 

 

I also noticed that when changing the pad from a thicker to a thinner Not Revittyone or vice versa, the toposurface did not update. As you can see, I changed the sidewalk slab from 1’-2” back to 1’-0” and ended up with a 2” gap. Not Revising Instantly now, are we?

 

Anyway, I kept thinking about this as the issue kept cropping up all over the place while working on the above site model and I was tired of trial and error solutions. Finally I nailed down the problem behavior thanks to the previously mentioned observation about the elevation of the bleeding edge. The next series of images explain the problem and solution.

Bleeding

Bleeding analyzed

Bleeding coagulated

So the key is to model your pad so that without any slope arrow, it is in line with any other pad, at the lowest elevation. Then add the slope arrow to make the pad slope upwards. The slope arrow direction does not seem to matter so in the above example, it could be rotated 180 degrees with the head getting the 10’-0” offset and the tail remaining at 0, and the result would be the same. Hope this is helpful!


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5 comments:

SpunkyMom said...

Thanks! Have had this come up a few times and did not come up with a solution...

Also - very much like your comment:

... especially because I have made a pact with the devil to obliterate the perception that only SketchUp is adequate for this phase!

SpunkyMom said...

Thanks! Have had this come up a few times and did not come up with a solution...

Also - very much like your comment:

... especially because I have made a pact with the devil to obliterate the perception that only SketchUp is adequate for this phase!

David Light said...

Great tip....I have had this issue a number of times and was not sure why it worked and other times it didn't!

ravi chandra said...

Great Tip.. !!! Thank u soo much.. !!!

Anonymous said...

Thanks, it really works !

Jorge

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