Incorrect volume calculation for complex object from 3D-Print toolbox #79394

New Issue

Alexis Maizel · 2020-07-30T15:22:38+02:00

Alexis Maizel commented

2020-07-30 15:22:38 +02:00

System Information
Operating system: macOS 10.14.6
Graphics card: Intel Iris Plus Graphics 655

Blender Version
Broken: 2.83.3
Worked: -

Short description of error
When using the 3D-Print toolbox (or any code using bmesh.types.BMesh.calc_volume()) to calculate the volume of a complex closed object I noticed that the volume calculation is incorrect if the object is moved far away from the 0,0,0 mark and becomes more incorrect the further the 3D object is displaced from the 0,0,0 origin.
No problems if the object is a simple cube. This was readily reported (https://developer.blender.org/T73295) and marked as resolved, but the problem remains for complex objects.

Exact steps for others to reproduce the error
*Add a Monkey head at the 0,0,0 mark in blender.
*Use 3D-Print toolbox to calculate volume, note that the volume is 2255372 cm cubed.
*Use transform location and move object 100m units in x, y & z directions.
*Re do volume calculation in 3D-Print toolbox, the volume should now say 5561196 cm cubed.
*Volume of the standard cube (8000000 cm3) is the same irrespective of the location (indeed fixing the issue raised in https://developer.blender.org/T73295).

Many thanks in advance.

**System Information** Operating system: macOS 10.14.6 Graphics card: Intel Iris Plus Graphics 655 **Blender Version** Broken: 2.83.3 Worked: - **Short description of error** When using the 3D-Print toolbox (or any code using `bmesh.types.BMesh.calc_volume()`) to calculate the volume of a complex closed object I noticed that the volume calculation is incorrect if the object is moved far away from the 0,0,0 mark and becomes more incorrect the further the 3D object is displaced from the 0,0,0 origin. No problems if the object is a simple cube. This was readily reported (https://developer.blender.org/T73295) and marked as resolved, but the problem remains for complex objects. **Exact steps for others to reproduce the error** *Add a Monkey head at the 0,0,0 mark in blender. *Use 3D-Print toolbox to calculate volume, note that the volume is 2255372 cm cubed. *Use transform location and move object 100m units in x, y & z directions. *Re do volume calculation in 3D-Print toolbox, the volume should now say 5561196 cm cubed. *Volume of the standard cube (8000000 cm3) is the same irrespective of the location (indeed fixing the issue raised in https://developer.blender.org/T73295). Many thanks in advance.

Alexis Maizel commented

2020-07-30 15:22:38 +02:00

Added subscriber: @alexis.maizel

Robert Guetzkow commented

2020-07-30 15:28:56 +02:00

Added subscriber: @rjg

Robert Guetzkow commented

2020-07-30 15:28:56 +02:00

This could potentially be fixed by 0ab66dd63f if it has the same cause as #79369. I haven't had time to test this though.

This could potentially be fixed by 0ab66dd63f if it has the same cause as #79369. I haven't had time to test this though.

Philip Holzmann commented

2020-07-30 18:27:29 +02:00

Added subscriber: @Foaly

Philip Holzmann commented

2020-07-30 18:27:29 +02:00

Keep in mind that calculating the volume reliably can only work on manifold meshes.
The default Suzanne mesh is not manifold.

However, it would of course be better if it could compute a reasonable approximate volume even in the non-manifold case.

Keep in mind that calculating the volume reliably can only work on manifold meshes. The default Suzanne mesh is not manifold. However, it would of course be better if it could compute a reasonable approximate volume even in the non-manifold case.

Alexis Maizel commented

2020-07-31 08:49:21 +02:00

@Foaly: Thanks for the note. Indeed, "fixing" the Suzanne mesh to make it manifold does make the volume calculations invariant with regard to location. I guess this is not really a bug but a limitation.

Richard Antalik commented

2020-08-02 00:38:47 +02:00

Added subscriber: @iss

Richard Antalik commented

2020-08-02 00:38:47 +02:00

Changed status from 'Needs Triage' to: 'Archived'

Richard Antalik closed this issue

2020-08-02 00:38:47 +02:00

Richard Antalik self-assigned this 2020-08-02 00:38:47 +02:00

Richard Antalik commented

2020-08-02 00:38:47 +02:00

Following steps now this looks like it's resolved now, so will close regardless of being limitation.

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Incorrect volume calculation for complex object from 3D-Print toolbox #79394