@sdmitch said:

It should if "point" is truly inside the solid. If it is a model point then it will need to be transformed by the inverse of the solid's transformation.

Thanks
Yes the point must be in the solid(group) coordinate space.

I've changed the code a bit to allow shell (outer face) testing
Here it is:

Edited:
After some testing still something was not OK.
I realized that when the ray crosses an edge it hits 2 different planes and through a vertice it can hit an unknown number of faces. The solution I came is that the ray crosses the solid in only one point. So instead of keeping track of how many faces it hits, I register all points the ray hits the solid and then perform a uniq-like operation to the array to count the number of points/hits.
I've updated the code.

For the filtering uniq! doesn't work (guessing because it uses eql? and this is not implemented in Point3d)
Also tried

pts.uniq! {|pt| pt.to_a}

but it didn't worked, but since the raycast is parallel to X axis comparing x coordinate does the trick

def point_insidesolid?(point, solid, exclude_surface=false)		
		vect = Geom;;Vector3d.new(1,0,0)
		pts = []
		solid.entities.grep(Sketchup;;Face).each do |face|
			if(FaceTools.is_pointof_face?(point,face))
				return true unless exclude_surface
				return false
			else
				pt = Geom.intersect_line_plane([point,vect], [face.vertices[0].position, face.normal])
				if(!pt.nil?)
					if(FaceTools.is_pointof_face?(pt,face) && pt.x>point.x)
						pts.push pt
					end
				end
			end
		end
		
		ptsuniq = pts.uniq {|pt| pt.x}

		return ptsuniq.count%2!=0
	end

	def point_insideface?(point,face)
		case(face.classify_point(point))
			when Sketchup;;Face;;PointInside, Sketchup;;Face;;PointOnVertex, Sketchup;;Face;;PointOnEdge
				return true
		end
		
		return false
	end

Is this OK?
The same principle. A raycast from the testing point. I'm only counting how many faces it sees in one direction and only if the point hits the face on the inside (from the testing point)
To also include the outter shell of the solid the point classification must be changed to validade Vertex and Edges hits.

Thanks

Here is the code

def point_insidesolid?(point, solid)
		return false unless solid.manifold?

		#vector that goes through the origin
		vec = Geom;;Vector3d.new(1,0,0).normalize
		counter = 0
		solid.entities.grep(Sketchup;;Face).each do |face|
			pt = Geom.intersect_line_plane([point,vec], [face.vertices[0].position, face.normal])
			if(!pt.nil?)
				if(face.classify_point(pt)==Sketchup;;Face;;PointInside)
					if(pt.x>point.x)
						counter +=1
					end
				end
			end
		end
		
		return false unless counter%2!=0
		return true
	end

I'm cooking something too.
Check out my blog http://paciente8159lab.blogspot.pt/2013/10/sketchup-3d-to-gcode-plugin.html