PolygonMesh#normal_at == [0, 0, 0]?

[Jim]

I'm trying to create a PolygonMesh from faces (works,) but does anyone know why the mesh normals are all Vector3d(0, 0, 0)?

model = Sketchup.active_model
entities = model.entities
selection = model.selection

mesh = Geom;;PolygonMesh.new
faces = entities.select{|e| e.is_a?(Sketchup;;Face)}

faces.each { |face|
    verts = face.outer_loop.vertices
    pts = verts.map{|v| v.position}
    mesh.add_polygon(pts)
}

mesh.count_points.times do |i|
    n = mesh.normal_at(i+1)
    p n
end

[thomthom]

Not sure... maybe it's populated only when you extract a mesh from existing faces....?

[TIG]

I you use mesh=face.mesh 4 what are the normals ?

[Jim]

Thanks, but how can I get more than a single face into the mesh using this?

@unknownuser said:

Why do you expect mesh = Geom::PolygonMesh.new to create normals for you?

If a mesh exists and has polygons, the normals can be calculated. I was hoping this would be done by SketchUp internally. I'm not even sure of the meaning of "normal" in this case - does it mean vertex normal, face normal, or something else.

[tomasz]

@unknownuser said:

Face.mesh
The mesh method creates a polygon mesh that represents the face. See the PolygonMesh class for more information.

Valid flags are:

0: Include PolygonMeshPoints,
1: Include PolygonMeshUVQFront,
2: Include PolygonMeshUVQBack,
4: Include PolygonMeshNormals.

mesh=face.mesh 4

Why do you expect mesh = Geom::PolygonMesh.new to create normals for you? You have passed just points. I guess normals simply aren't initialized or default to 0,0,0.

[tomasz]

@jim said:

Thanks, but how can I get more than a single face into the mesh using this?

Polygonal mesh is a set of triangles. You could write a method to merge several faces into one polygonal mesh. There is no such a solution in Ruby API.

[tomasz]

@jim said:

I'm not even sure of the meaning of "normal" in this case - does it mean vertex normal, face normal, or something else.

From my experience and understanding the "normal" here is a normal of a vertex in a face. If a face has one edge smoothed, it can result in two normals at those two vertexes different then face.normal.

[TIG]

What I'd normally do is get each face's mesh [with normals etc] then export each face in the mesh with its normals.
Why do you want to export a mesh made from a combo of faces ?
Aren't you going to export the faces of each face's mesh one by one anyway ??

[tomasz]

I guess Jim wants to weld all vertices... or at least export one material as one mesh.

[Jim]

Just looking for a shortcut way to get vertex normals. I know it can be done in Ruby, but was hoping SketchUp did it faster when using a PolygonMesh.