Knowledgebase: AutoCAD Civil 3D
Dealing with Surface Hide Boundaries when Pasted into Another Surface
Posted by Shane O'Rorke, Last modified by Shane O'Rorke on 30 April 2010 11:40 AM

When you have a Design Surface that includes Hide Boundaries and you Paste it into a (copy of) your Natural Surface, the area in the Hide Boundary does not display the Natural Surface triangulation.  What do I do to fix this?

Unfortunately AutoCAD Civil 3D doesn't respect hide boundaries of a pasted surface the way you may expect - in 2009 and earlier versions it simply triangulated across the hide boundary, and in 2010 there is a 'hole' in the surface where the hide boundary was applied.  Normally when you paste a design surface on top of an existing surface you want the existing surface to display wherever you don't have your design surface, including in the hide boundaries of the design surface.

The answer, in short, is to create a copy of the existing surface, apply the hide boundary as an outer boundary, and then paste this on top of the merged surface.  Essentially this takes a chunk of the existing surface and slams it in the hole.

Starting with three surfaces; Natural Surface, Design Surface and Merged Surface (this is the paste of Design Surface on top of Natural Surface, the steps to infill a hole is:
1. Make sure you can see the polyline used as a Hide boundary for the Design Surface - this will become the outer boundary of your 'infill' surface
2. From the Civil 3D Toolspace, right click on Surfaces and select 'Create Surface'.  Make a new surface and give it a name (eg: Natural Surface Infill).  You may want to set the style to 'no display' so it doesn't show up on screen (maybe change the style once you are sure it looks how you think it should)
3. Expand this new surface to get to the Definition.  Right click on Edit and choose the option 'Paste Surface'  Select the Natural Surface as the surface to paste.
   You now have an exact replica of the existing surface
4. From the Definition of this new surface, right click on Boundaries and select Add.  Make an Outer boundary and tick ON the option for a 'Non-destructive Breakline'.  Select the polyline that represents the hide boundary of the design surface.  You should get a replica of the Natural Surface that sits over the hole
5. Expand out your finished merged surface (eg: Merged Surface) to get to the Definition.  Right click on Edit and choose the option 'Paste Surface'.  Paste in the new surface (eg: Natural Surface Infill).

The Merged Surface should now accurately describe the natural surface levels in the hole of the design surface.  Repeat this process for each hole.

Version: Civil 3D 2010, 09, 08, 07 ,06

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