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Surface boundary - zero volume

Question asked by Stevie McCafferty on Oct 29, 2019
Latest reply on Oct 29, 2019 by Tim McClannahan

I have seen a recent post with a similar issue to this, but am wondering if there is an improved workflow that might help avoid this happening in the first place...

 

When trying to calculate a surface to surface volume constrained to a boundary, I am getting zero volume, and zero triangulated area.  When I make a duplicate of the boundary, and re-attempt the exercise, I get normal volume and triangulated area reported.

 

What is causing the error in the first boundary, and is there a way to easily avoid this (noting previous comments suggesting a small horizontal offset... while this does appear to work, it is not ideal in all cases - and for very large boundaries, even a small offset can result in a change in area that leaves work open to scrutiny).

 

I have attached an extract of the project file in question.  Calculating volumes from surface "Made Ground" to surface "FGL-450mm Oct19".  The problem occurs when using boundary on layer "SiteDBoundary" (Problem Boundary), but is ok when using boundary on layer "SiteDBoundary-COPY" (Copy Boundary).

 

Appreciate your thoughts / insight - many thanks in advance.

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