Question about Normal vector

gerard.degreve

Hi everybody,

I'm a beginner in the study sketchup API's.

I don't understand the following behavior: If I test the normal vector of a face before and after a rotation, it does not seem to change.

Here is my code:

ent = Sketchup.active_model.entities
face = ent.add_face [0,0,0], [1,0,0], [1,1,0], [0,1,0]
face.reverse!
face.pushpull 1

group1 = ent.add_group face.all_connected

puts face.normal

rot=Geom;;Transformation.rotation(Geom;;Point3d.new(0, 0, 0), Geom;;Vector3d.new(0, 1, 0), 30.degrees)
ent.transform_entities rot, group1

puts face.normal,"_______________________"

group1.entities.each{|e| 
	if e.typename =="Face"
		puts e.normal
	end
}

and here is the ruby console return:

load "Tests/testnormalvector.rb"
(0.0, 0.0, -1.0)
(0.0, 0.0, -1.0)
_______________________
(0.0, 0.0, -1.0)
(0.0, 0.0, 1.0)
(0.0, -1.0, 0.0)
(1.0, 0.0, 0.0)
(0.0, 1.0, 0.0)
(-1.0, -0.0, -0.0)
true

The normal vector still point to the same direction. If I loop on each faces.normal of my object, the results are the same as if there was no rotation.

Have I missed something?

My goal is to rotate gradually an entity and stop the rotation when the normal vector of a reference face reaches a certain direction.

I'm using Sketchup 7 pro.

Thank you in advance

Gerard

thomthom

First of all - when making groups using the Ruby API you change the order of who you make things.

You make the group first, then add the content:

<span class="syntaxdefault"><br />ent&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">Sketchup</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">active_model</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">entities<br />group1&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">ent</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">add_group<br /><br />face&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">group1</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">entities</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">add_face</span><span class="syntaxkeyword">(&nbsp;[</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">],&nbsp;[</span><span class="syntaxdefault">1</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">],&nbsp;[</span><span class="syntaxdefault">1</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">1</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">],&nbsp;[</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">1</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">]&nbsp;)<br /></span><span class="syntaxdefault">face</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">reverse</span><span class="syntaxkeyword">!<br /></span><span class="syntaxdefault">face</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">pushpull&nbsp;1<br /></span>

Grouping existing geometry can lead to problems very easily.

Also, #typename is tertrible slow. Read this for more info: http://www.thomthom.net/thoughts/2011/12/never-ever-use-typename/

If you're new to SketchUp plugin development I also recommend you read this:
http://www.thomthom.net/thoughts/2012/01/golden-rules-of-sketchup-plugin-development/

(Still looking at the code and question you asked.)

thomthom

Ah! You're rotating the group itself. The vector you're reading from the face remains contant because within the group itself the face hasn't moved. You get the local coordinate of the face.

If you want the global you need to transform the face normal with the group's transformation as well as the current edit context. http://www.sketchup.com/intl/en/developer/docs/ourdoc/model#edit_transform

More info on instances and definitions in SketchUp:
http://www.thomthom.net/thoughts/2012/02/definitions-and-instances-in-sketchup/

TIG

You put a face in a group.
It has a face.normal.
You then rotate the group:
ent.transform_entities(rot, group1)
the group rotates but its contents stay in the same relationship to the group's axes.
The face is still inside the group's context and it's unchanged, so the face.normal is unchanged, since it's reported relative to the group's axes.
If you rotate the group's contents:
group1.entities.transform_entities(rot, group1.entities.to_a)
Then the face.normal will change.
You can also get the group.transformation and apply that to the face.normal, as face.normal.transform!(group.transformation) etc... You need to decide if you want to transform the group or the face inside it...

gerard.degreve

Got it!

I suspected that the problem was that the normal vector's coordinates are expressed relative to the axes of the object.

Thank you for your explanations and your valuable advice.

Gerard

jolran

if e.is_a?(entity) should work better. Can't put space between certain arguments.

TIG

if e is_a? Sketchup::Face ==NO ==missing '.'
if e.is_a? Sketchup::Face ==YES
or better
if e.is_a?(Sketchup::Face)

jshaz

Hi guys, I'm trying to find the normal of a face that i have selected in my model I thought something similar to this script shown below might do the trick but alas it hasn't. The ruby console says I have an undefined method e. With my limited ruby brain I though this might be helped by making e = [] or e = 0 which of course it did not. I have used similar script to this below for finding areas. Any help or advice is greatly appreciated. Thanks

<span class="syntaxdefault">model&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">Sketchup</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">active_model<br />ents&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">Sketchup</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">active_model</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">entities<br />sel&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">model</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">selection<br />mat&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">sel</span><span class="syntaxkeyword">[</span><span class="syntaxdefault">0</span><span class="syntaxkeyword">].</span><span class="syntaxdefault">material&nbsp;&nbsp;</span><span class="syntaxcomment">#&nbsp;selected&nbsp;items&nbsp;with&nbsp;material&nbsp;we&nbsp;are&nbsp;interested&nbsp;in<br /></span><span class="syntaxdefault">normal_vector&nbsp;</span><span class="syntaxkeyword">=&nbsp;</span><span class="syntaxdefault">0<br /></span><span class="syntaxcomment">#&nbsp;go&nbsp;through&nbsp;all&nbsp;the&nbsp;entities<br /></span><span class="syntaxdefault">ents</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">each&nbsp;</span><span class="syntaxkeyword">do&nbsp;|</span><span class="syntaxdefault">e</span><span class="syntaxkeyword">|<br />if&nbsp;</span><span class="syntaxdefault">e&nbsp;is_a</span><span class="syntaxkeyword">?&nbsp;</span><span class="syntaxdefault">Sketchup</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">Face&nbsp;&nbsp;</span><span class="syntaxcomment">#&nbsp;if&nbsp;e&nbsp;is&nbsp;a&nbsp;face<br /></span><span class="syntaxkeyword">if&nbsp;</span><span class="syntaxdefault">e</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">material</span><span class="syntaxkeyword">==</span><span class="syntaxdefault">mat&nbsp;&nbsp;</span><span class="syntaxcomment">#if&nbsp;e&nbsp;material&nbsp;is&nbsp;the&nbsp;material&nbsp;of&nbsp;the&nbsp;selected&nbsp;entity<br /><br />#&nbsp;normal&nbsp;equals&nbsp;initial&nbsp;normal&nbsp;vector&nbsp;plus&nbsp;the&nbsp;new&nbsp;normal&nbsp;vector<br />#this&nbsp;returns&nbsp;the&nbsp;normal&nbsp;of&nbsp;the&nbsp;selected&nbsp;face<br /></span><span class="syntaxdefault">normal_vector&nbsp;</span><span class="syntaxkeyword">=&nbsp;&nbsp;</span><span class="syntaxdefault">normal_vector&nbsp;</span><span class="syntaxkeyword">+&nbsp;</span><span class="syntaxdefault">face</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">normal<br /><br />end&nbsp;&nbsp;</span><span class="syntaxcomment">#end&nbsp;if<br /></span><span class="syntaxdefault">end&nbsp;&nbsp;</span><span class="syntaxcomment">#end&nbsp;if<br /></span><span class="syntaxdefault">end&nbsp;&nbsp;</span><span class="syntaxcomment">#end&nbsp;loop<br /><br /></span><span class="syntaxdefault">puts&nbsp;normal_vector</span>

Dan Rathbun

this:
normal_vector = normal_vector + face.normal

will not work as expected, if you set normal_vector to reference the integer object 0, because the integer +() method will get called, and it is not likely that it would know how to handle an argument that references a Geom::Vector3d object.

Smarter to create either a unit vector object to start with, or a zero length vector:
normal_vector = Geom::Vector3d.new(0,0,0)

THEN, when you call the +() method using:
normal_vector = normal_vector + face.normal
the special vector addition API method will get called.

In other words your statement is evaluated as if it were written:
normal_vector.=( normal_vector.+( face.normal ) )

This is one of the important things about Ruby... = and + (etc,) are not really operators, they are instance method names.