Author Topic: Projected surface area mismatch  (Read 65 times)

gvdpeor

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Projected surface area mismatch
« on: October 29, 2018, 11:17:19 PM »
I've been getting an error when using triangle volume to compute volume between two surfaces. My Original surface is larger than my design surface by several times but I continue to get 'Projected surface area mismatch' errors when I attempt an almost exact calculation. My design surface is just a cut into the original surface and is not complicated at all.
Any idea what could cause that?

Lars

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Re: Projected surface area mismatch
« Reply #1 on: October 30, 2018, 07:09:37 PM »
Probably some problems with overlapping triangles. Check your indata, crossing breaklines may cause the problem. The original surface should be larger than the design so that is correct.

The "Almost Exact" option projects the design triangles to the original surface and then add all projected triangles as breaklines to the original surface and creates new triangles. This method makes it possible to create prismoids that match both surfaces. The error should contain a value of the size of the mismatching area, if this is small you may consider if you can use the volume anyway.

gvdpeor

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Re: Projected surface area mismatch
« Reply #2 on: October 30, 2018, 07:16:29 PM »
OK. Thanks for your input. I'm using an OG surface generated from contours so it is complicated and hard to debug. The error is around 1% so I will assume the result is reasonable.

Lars

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Re: Projected surface area mismatch
« Reply #3 on: October 30, 2018, 07:29:38 PM »
You can check your contours for duplicate points, there is a tool for that in CadTools. Duplicate points can be a problem.