Bug calculating surface area and volume
Closed, InvalidPublic

Description

System Information
Windows 7 Professional and AMD Radeon Graphics Processor (0x6610)

Blender Version
Broken: Blender 2.78a e8299c8
Worked: (optional)

Short description of error

Code for volume and surface area does not match output of volume and surface area calculated using 3D print tools. Working on the cube made in the create panel, when slicing the cube in half and recreating it using the mirror modifier output of the code and 3D print tools matched, but values were double what they should have been, and when a triangular prism was created using the mirror modifier 3D print tool calculations were close to correct, surface area calculated from the code was correct, but the volume calculated using the code was completely off. The reason I started testing this was because I have a 3D model of a whale created using the mirror modifier (set to scale and everything) and the calculations for SA and V seemed completely off. I apologize if this isn't a bug, someone suggested it might be. I'm very new to blender. If you have a suggestion for more accurate SA and V calculations for complex meshes please let me know.

Exact steps for others to reproduce the error
Run code in python in file, check against values from 3D print tools{F1325085}

Based on a (as simple as possible) attached .blend file with minimum amount of steps

Details

Type
Bug
Campbell Barton (campbellbarton) lowered the priority of this task from Normal to Incomplete.Dec 19 2017, 6:56 AM

Attached file is a shortcut, please upload the original file.

Like it was said, we cannot do much without a way of recreating it with a proper blend file.

More than a week passed without a reply.

Due to the tracker policy, archiving until the required additional information / data is provided.

I apologize for the delay, I have been in the field without internet access.

Please let me know if this upload works. I am very new to Blender and therefore am still learning the ins and outs. I'm sorry for any inconvenience this may have caused.

Have a happy New Year,

Steph

Vuk Gardašević (lijenstina) reopened this task as Open.EditedJan 3 2018, 9:59 AM
Vuk Gardašević (lijenstina) raised the priority of this task from Incomplete to Needs Triage.

Since the requested file was provided, reopening the task.
There is a difference between the bmesh volume calculation provided in the blend file script and the statistics for in the add-on.
The mesh is simple and mirrored. Haven't checked which one of those is wrong as how should the modifier case be handled correctly.

As an addition to this problem I've noticed discrepancies when using the area tool from the Measureit add-on, so there is a difference between calculations in bmesh, the measureit addon, and 3D printing add-on, and the area provided by "Face info" in the properties panel. Just wanted to insure you had all of the necessary information.

Thank you,

Steph

BMesh's from_object doesn't apply constructive modifiers (only the option to apply deformation modifiers).

To apply all modifiers you'll need to use Object.to_mesh.

Thank you for addressing this, however I still believe there is an error with the area and volume calculations. As per my previous comment when simply calculating area of a plane there are different calculations using the measureit add-on and area providing by the "Face info" option in the properties panel.