Python data do not accord with the value that show_extra_face_area displays. #44316

New Issue

perfection cat · 2015-04-09T01:48:20+02:00

perfection cat commented

2015-04-09 01:48:20 +02:00

System Information
Windows XP/SP3 32bits

Blender Version
Broken: version 2.74 (sub 4), branch b'master', commit date b'2015-04-08' b'00:38', hash b'8c539b0', b'Release'
Worked: unknown

Short description of error
Python data do not accord with the value that show_extra_face_area displays.
Exact steps for others to reproduce the error
The value of the area that I can access in Python does not agree with the value of an area displayed by 3DView.

face_area.blend

**System Information** Windows XP/SP3 32bits **Blender Version** Broken: version 2.74 (sub 4), branch b'master', commit date b'2015-04-08' b'00:38', hash b'8c539b0', b'Release' Worked: unknown **Short description of error** Python data do not accord with the value that show_extra_face_area displays. **Exact steps for others to reproduce the error** The value of the area that I can access in Python does not agree with the value of an area displayed by 3DView. ![face_area.png](https://archive.blender.org/developer/F159985/face_area.png) [face_area.blend](https://archive.blender.org/developer/F159987/face_area.blend)

perfection cat commented

2015-04-09 01:48:20 +02:00

Changed status to: 'Open'

perfection cat commented

2015-04-09 01:48:20 +02:00

Added subscriber: @sindra1961

Campbell Barton commented

2015-04-09 02:20:57 +02:00

Changed status from 'Open' to: 'Archived'

Campbell Barton closed this issue

2015-04-09 02:20:57 +02:00

Campbell Barton self-assigned this 2015-04-09 02:20:57 +02:00

Campbell Barton commented

2015-04-09 02:20:57 +02:00

This isnt really a bug.

Whats happening is there are 2 different methods used to calculate area:

View-port drawing accumulates tessellated triangle areas.
The Python API uses the cross product of a polygon divided by its length.

We could use the same method for both but the first method is faster, so its used for drawing.

In you example the faces are non-planar, (not flat) so the answers are slightly different.

closing.

This isnt really a bug. Whats happening is there are 2 different methods used to calculate area: - View-port drawing accumulates tessellated triangle areas. - The Python API uses the cross product of a polygon divided by its length. We could use the same method for both but the first method is faster, so its used for drawing. In you example the faces are non-planar, (not flat) so the answers are slightly different. closing.

perfection cat commented

2015-04-09 02:57:47 +02:00

I understood what you meant.
But is there predominantly more object which is not flat?
Then may I recognize that python data shows the accurate area of the shape?

I understood what you meant. But is there predominantly more object which is not flat? Then may I recognize that python data shows the accurate area of the shape?

Campbell Barton commented

2015-04-09 04:43:45 +02:00

@sindra1961, for non flat faces - the area is undefined. (you get different answers depending on how you calculate it.)

In this case though, I think Python's result is more accurate, since its always the same - independent of triangle tessellation.

@sindra1961, for non flat faces - the area is undefined. *(you get different answers depending on how you calculate it.)* In this case though, I think Python's result is more accurate, since its always the same - independent of triangle tessellation.

perfection cat commented

2015-04-09 05:18:48 +02:00

I thank for what you replied.
I think that nobody is at a loss if python API document has the explanatory note about it.
Finally I thank for your correspondence once again.

I thank for what you replied. I think that nobody is at a loss if python API document has the explanatory note about it. Finally I thank for your correspondence once again.

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Python data do not accord with the value that show_extra_face_area displays. #44316