wrong area and volume (larger convex hull)

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DA523
Posts: 166
Joined: Mon May 25, 2020 4:02 pm

wrong area and volume (larger convex hull)

Post by DA523 »

I am trying to find area and volume of simple XYZ points
I got wrong area because convex hull code make larger perimeter with out any way to correct the hull manually (segment tool does not help)
I can get nice hull with QGIS very easily
but I want same hull result in CC for correct are and volume
please help
how to get same hull in CC or how to modified manually before calculation?
Last edited by DA523 on Tue May 26, 2020 12:14 am, edited 1 time in total.
daniel
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Re: wrong area and volume (larger convex hull)

Post by daniel »

How did you generate the 'hull' here?

And what are these white points? (there are not a lot ;)
Daniel, CloudCompare admin
DA523
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Re: wrong area and volume (larger convex hull)

Post by DA523 »

hulls is generated by CC prior to any 2.5D volume calculation or even mesh
but as you can compare with hull by QGIS
CC hull is larger and can make area and volume +20% ore more (stockpile calculation)
DA523
Posts: 166
Joined: Mon May 25, 2020 4:02 pm

Re: wrong area and volume (larger convex hull)

Post by DA523 »

here I attacked example
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DA523
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Re: wrong area and volume (larger convex hull)

Post by DA523 »

I think forum can only attach one image per post
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WargodHernandez
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Re: wrong area and volume (larger convex hull)

Post by WargodHernandez »

Are you expecting CC to produce a concave hull? I thought we only have convex hull generation. That would explain the difference
daniel
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Re: wrong area and volume (larger convex hull)

Post by daniel »

Well, my question was really "how" did you generate the hull? With the 'Edit > Fit > Facet' tool?

Because there's a way to generate a concave hull, but not as a polygon. And mind also that the 'Facet' tool doesn't generate a flat polygon, but a 2.5D one.

Anyway, I agree with Chris, here it definitely looks like a convex hull, and not a concave one.
Daniel, CloudCompare admin
DA523
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Re: wrong area and volume (larger convex hull)

Post by DA523 »

OK it clear to me the difference between convex and concave
so how to tell CC to use concave not convex to calculate area and volume?
because it is more accurate to use concave
The goal is stockpile volume calculation
daniel
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Re: wrong area and volume (larger convex hull)

Post by daniel »

Well as I said that's not possible for a mesh or facet.
Daniel, CloudCompare admin
DA523
Posts: 166
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Re: wrong area and volume (larger convex hull)

Post by DA523 »

OK, that means CC is bad choice for any volume calculation.
2.5D volume or mesh volume is misleading and must be avoided for any real application.
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