Getting normal to cylinder face

[peterjohnson84]

Hi there,

I am having some trouble with some code I'm writing and was wondering if there was a simple solution that I'm unaware of.

My aim is to find vector the normal to a cylinder face (where the cylinder has beeen 'stored' as a group) and from that, work out the orientation of the cylinder group. So far, I have been able to do this for a cylinder which I created. However if I rotate the cylinder and perform the same operation, the normal vector does not change with the rotation i.e. if I create a cylinder aligned along the z axis - circle.normal will always give (0,0,1) despite any rotation i perform on the group.

I assume the information about the rotation is stored somewhere and from this I could work out the cylinder orientation - but I'm at a loss to work out how to do this.

Any help with this would be greatly appreciated.

[TIG]

Try adjusted_normal=face.normal.transform!(group.transformation)
where 'group' is the container of the circle-'face' on the end?

[peterjohnson84]

Cheers TIG, that did the trick.

[bentleykfrog]

Just answered my own question, transformation is relative to the parent.

Here's some more compact code:

normal = entity.normal
for i in (0..(path_to_entity.length-2)) do
  e = intersect_path[i]
  normal = normal.transform! (e.transformation)
end

[bentleykfrog]

@tig said:

Try adjusted_normal=face.normal.transform!(group.transformation)
where 'group' is the container of the circle-'face' on the end?

Sorry for digging up an old topic, but will this work with nested groups/component instances?

normal = entity.normal
i = 0
path_to_entity.each {|entity|
  i +=1
  break if i >= path_to_entity.length
  normal = normal.transform! (entity.transformation)
}

Or does transform represent a transformation from the models axes? (ie, just require normal = normal.transform! (entity.transformation)

Just for background, I'm trying to get a model based vector of the face normal as in peterjohnson84's example