Thursday, March 15, 2012

Interactive Terrain Shaping - Combining Cut and Fill

In an earlier post, I created a building pad by creating a fill grid from a bounded flat plane.  This was slick and simple because the entire plane was above the existing ground surface - it was in fill.  But what if part of the plane is in cut and part in fill?  That's what I'd like to dive into in this post.  You should check out the earlier post before continuing because I don't lay it out step by step in this post.
I've broken out the old standby Shaker surface that has been in the LDT and Civil 3D tutorials for as long as I can remember.  I like this one in this case because its a nice, steep slope.  I'll start the explanation with the work canvas already in place.


I'll create a flat plane and a fill grid, just like before.

Now, using a very similar process, I'll create a cut grid from the same flat plane.

The I'll use the Top Envelope command to add the fill grid to finished ground.  Before this step, Finished Grid = EG surface.  In this example, the fill zone is a fairly small area on the lower left corner.


Finally I'll use the Bottom Envelope command to add the cut grid to the Finished Grid.  Before this step, Finished Grid = EG surface + Fill Grid.  The result is the combination of cut and fill applied all at once, just like you'd expect.

I tried this out using the Add Fill and Remove Cut custom commands and they did speed up the process a little but it was still two separate operations for cut and fill.  I like doing it first using basic elements to gain an understanding, then using the custom commands to do it quicker but still understand what's going on.




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