CGTalk - Select Face by Normal

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blenderman0815

12-19-2007, 07:01 PM

Simple Script to select top faces.

myFaceNumbers = polyOp.getNumFaces $
MySelectionSet=#()

for i = 1 to myFaceNumbers do
(
myFace = i
myNormal = polyOp.getFaceNormal $ myFace

if myNormal == [0,0,1] then
(
join MySelectionSet #(myFace)
Print MySelectionSet
)
)

setFaceSelection $ MySelectionSet

Bobo

12-21-2007, 07:44 AM

It is a better idea to calculate the angle between the desired vector (in your case [0,0,1]) and the face normal and compare to a threshold.

theVector = [0,0,1]
theThreshold = 0.01
theAngle = acos(dot theNormal theVector)
if theAngle <= theThreshold do ...

Because Point3 value components are floats, sometimes a normal pointing up might have a floating point imprecision and not be exactly [0,0,1] while still VERY close to it. Also , if you want all normals that are +/- 10 degrees from the reference direction, you can just set theThreshold to 10 and fire away...

blenderman0815

12-21-2007, 08:24 AM

Threshold ! :lightbulb

Bobo reads my thoughts. Exactly what I need, thank you.

Bobo

12-21-2007, 08:29 AM

Threshold ! :lightbulb

Bobo reads my thoughts. Exactly what I need, thank you.

Keine Ursache! :)

Btw, keep in mind that both vectors used in the DOT function should be normalized. Normally, face normals are normalized, but just to be completely sure you can say

theAngle = acos ( dot (normalize theNormal) (normalize theVector) )

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12-21-2007, 08:29 AM

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