Face.plane?

thomthom · 25 Jan 2009, 22:25

I'm trying to work out the values of Face.plane. Am I right that the first three numbers is the normal?

But what's the fourth?

Matt666 · 25 Jan 2009, 22:46

Hi Thomthom!
I will try to tanslate an answer from Didier here :
Plane returns an array of four values :

First three numbers is the normal of the face
Fourth number is the elevation (distance Z) of the plane.

Draw a face with Z = 0.
Try to move your face on 1 meter on Z.
Face.plane will return [0,0,1,39.3700787401575] (39.3700787401575 = 1m in inches).

thomthom · 26 Jan 2009, 08:14

I don't think the D is purely elevation. I thought that initially, but when I did some test I saw something: If I drew I single square flat, then copied that upwards, both these squares had the same plane, even though they where at different Z-position. If I added another square to one of them standing 90 degrees upwards, connected, the last number of the plane changed, even though I hand not made any changes to the face itself, only connected another face to it. That puzzles me.

tbd · 26 Jan 2009, 11:47

thomthom: attach the model and the code for testing. a face that have a different Z should have a different plane equation

Didier Bur · 26 Jan 2009, 14:09

Hi,
As said before, Ax + By + Cz + D = 0 is the equation of a plane, where A,B and C are the vector coordinates of the normal to the plane, and D is the shortest distance between a point on the plane and the origin 0,0,0, that's to say it is the intersection of a line normal to this plane (passing through point 0,0,0) and the plane itself.
A,B,C give the plane its "orientation" around the axes, and D its distance to zero.
Hope this helps,

avariant · 26 Jan 2009, 15:00

Isn't it the plane equation: Ax + By + Cz + D = 0 ?
A,B,C is the normal, D is an offset (though I don't think you can say it's the "elevation"; it's more like if you placed the normal vector at the origin, it's the distance along that vector until you intersect the plane. It can be elevation, but could just as easily be along any arbitrary axis).

thomthom · 26 Jan 2009, 15:14

@unknownuser said:

thomthom: attach the model and the code for testing. a face that have a different Z should have a different plane equation

Didn't save it. Can't reproduce it with a new file either. Must be my head going bonkers last night.

thomthom · 26 Jan 2009, 15:15

Thanks for the heads up people.

Wish that API wiki truly was a wiki so that info could have been added there.