Question about the vector direction

wing8b

Hi, I am new to Sketchup and Ruby, and I am now using SketchUp 7.

I wonder why the following 2 scripts would have the same result. I suppose them should be in opposite direction...

Script#1:
` centerpoint = Geom::Point3d.new

Create a circle perpendicular to the normal or Z axis

vector = Geom::Vector3d.new 0,0,1
vector2 = vector.normalize!
model = Sketchup.active_model
entities = model.active_entities
edges = entities.add_circle centerpoint, vector2, 5
face = entities.add_face edges
status = face.pushpull 100, true`

Script#2:
` centerpoint = Geom::Point3d.new

Create a circle perpendicular to the normal or Z axis

vector = Geom::Vector3d.new 0,0,-1
vector2 = vector.normalize!
model = Sketchup.active_model
entities = model.active_entities
edges = entities.add_circle centerpoint, vector2, 5
face = entities.add_face edges
status = face.pushpull 100, true`

Can anyone advise me on that? Thanks!

Chris Fullmer

Yes, it does exactly what you think it should. The vector in script 1 points upwards, while the other points downwards.

But in SketchUp, any face that is created on z = 0 (the groundplane) that face is always facing downwards. So that effectively overwrites the vector you used in making the circle. In both scripts, try changing the first line to

centerpoint = Geom::Point3d.new(10,10,10)

So that it creates the circle up off the groundplane. Then you will see the results you expect where script 1 the tube goes upwards and script 2 the tube goes downwards.

Hope that helps,

Chris

Chris Fullmer

A good practice might be to test the normal of the face after it is created. If it's z direction does not match the vector's z direction (vector points upwards but face points downwards) then you should reverse the face, and then proceed with the rest of the script.

MartinRinehart

This bit of code is unusual:


vector = ...
vector2 = vector.normalize!

By convention, Ruby methods that end with a "!" work directly on the calling object's data. So vector.normalize! normalizes vector. You now have the normalized data in vector and a second reference to it in vector2. Not sure that was what you intended.

I added a comment to the Vector3d class doc to clarify this. (If you learned from the doc you were misled.)