Hello to all,

There's something I don't understand (no, many things) and that's about pickray.
Suppose I have a model existing of a single edge. Then I create a ray from the eye through one of the two endpoints of the on screen projection and try to find the intersection of that ray with the edge. Why is the ray (a line) missing the edge? I'm totally confused because I presumed that the result had to be the startposition (or endposition, depending of the screencoordinates) of the edge.

An example

def exp_a
  mod = Sketchup.active_model
  view = mod.active_view
  ents = mod.entities
  ents.clear!
  edges = ents.add_edges([0, 0, 0] , [100, 100, 100]) 
  edge = edges[0]
  pt = view.screen_coords(edge.start.position)
  ray = view.pickray(pt.x, pt.y)
  Geom.intersect_line_line(edge.line, ray)
end

The result is nil.

Can anybody tell me what is wrong with my assumption that in this case the result should be [0, 0, 0]? What is wrong with my understanding of pickray?

Problem solved!!!
It's all about vectors. One of the arguments of the method that is resposable for creating the protrusions must be a vector or the order of the four given points of the rectangle must choosen in a way that the vector can be derived as the difference between the first two points of de rectangle.

` def findface(pt)
arr = Sketchup.active_model.entities.grep(Sketchup::Face)
arr.each {|f| return f if f.classify_point(pt) == Sketchup::Face::PointInside}
return nil
end

def body
ents = Sketchup.active_model.entities
ents.clear!
f = ents.add_face([0, 0, 0], [60, 0, 0], [60, 40, 0], [0, 40, 0])
f.pushpull(-30)
end

def protr(array, extrusion)
ents = Sketchup.active_model.entities
base = ents.add_face(array)
arcvector = array[1].vector_to(array[0])
basenormal = base.normal
depthvector = basenormal.cross(arcvector).reverse
width = array[1].distance(array[0])
depth = array[2].distance(array[1])
basenormal.length = extrusion - width/2
basecenter = Geom::Point3d.new
basecenter.x = (array[0].x + array[1].x)/2
basecenter.y = (array[0].y + array[1].y)/2
basecenter.z = (array[0].z + array[1].z)/2
center = basecenter + basenormal
base.pushpull(extrusion + 1)
ents.add_arc(center, arcvector, depthvector, width/2, 0, Math::PI)
basenormal.length = extrusion + 0.5
findface(basecenter + basenormal).pushpull(-depth)
ents.add_circle(center, depthvector, 1)
findface(center).pushpull(-depth)
end

def test
body
protr [[22.0, 8.0, 30.0], [22.0, 20.0, 30.0], [10.0, 20.0, 30.0], [10.0, 8.0, 30.0]], 14.0
protr [[35.0, 8.0, 30.0], [47.0, 8.0, 30.0], [47.0, 20.0, 30.0], [35.0, 20.0, 30.0]], 14.0
end`

The troubles appear in the following simplified case.

def example
  ents = Sketchup.active_model.entities
  ents.clear!
  # body
  pt0 = [0, 0, 0]
  pt1 = [10, 0, 0]
  pt2 = [10, 6, 0]
  pt3 = [0, 6, 0]
  ents.add_face(pt0, pt1, pt2, pt3).pushpull(-8)
  # protrusion 1
  pt0 = [2, 2, 8]
  pt1 = [4, 2, 8]
  pt2 = [4, 4, 8]
  pt3 = [2, 4, 8]
  ents.add_face(pt0, pt1, pt2, pt3).pushpull(6)
  center = [3, 2, 10]
  ents.add_circle(center, [0, 1, 0], 0.5)
  # protrusion 2
  pt0 = [7, 2, 8]
  pt1 = [9, 2, 8]
  pt2 = [9, 4, 8]
  pt3 = [7, 4, 8]
  ents.add_face(pt0, pt1, pt2, pt3).pushpull(6)
  center = [9, 3, 10]
  ents.add_circle(center, [1, 0, 0], 0.5)
end

I succeeded in writing a method that is able to place the spikes at all six (maybe more) sides of the body, no matter how the body is transformed in 3D. The problem is how to determine the face on which the circles (drilling holes) are placed. In the mean time I have found a solution that exists of an extra boolean parameter in the parameterlist of the method. But that's not a satisfactory solution: the choice of the parametervalue is a matter of trial and error (not such an attempt with just two possibilities). The method that generates the spikes now is something as 'dosomething(face, extrusion, semaphoor = true)'. I was hoping that all your answers lead me to the conclusion that the trial and error parameter 'semaphoor' is redundant.

Finally: the solution

The face I used was part of another face. And in that case it seems that the control over the order in which the vertices of the smaller face appear is taken over by the other face. Your answers helped me to discover that phenomenon. Is this assumption correct?

Thank for your help. I think your answers bring the solution within sight. My apologies for the rather stupid 'dosomething' method. At least I should have written 'dosomething(face, ..)'. And there exactly lies the bottleneck. Even if all the entities are erased at the very beginning of 'helpme' the problem still occurs in the method 'dosomething(face, ..)'. But I can smell the scent of a solution.

Thanks TIG
I think the solution indeed lies in matching - what you called - points and vpoints. I'm going to give it a try. It is a lot of work because my method 'dosomething' really exists of a couple of tranformations that required already all my knowledge of maths!!!

Still not happy with your answers.
Take a look at the next method, based on my old one.

` def helpme(a0, a1, a2, a3)
ents = Sketchup.active_model.entities
face = ents.add_face(a0, a1, a2, a3)
for i in 0..3
puts face.vertices[i].position
end

dosomething

end`

There are eight possibilities to define the rectangle but the output of the method will give seven times the same answer and exactly once a different one. I need all eight different answers. The dependency of clockwise/ccw is not really the problem because the method 'dosomething' already copes with this item.

@slbaumgartner said:

You provided the points in anti-clockwise order as seen from above, which means the normal vector to the face would point upward (+z). Entities#add_face automatically forces the normal of a face drawn at z=0 to point downward, which causes your vertices to be traced in the opposite (clockwise) order. You can reverse the face after drawing it to correct for this, but there is no option by which you can turn off this "feature".

Thanks for your quick response! It helps a lot but still it is not the total solution. A clockwise definition with four points can take place in four different way's, depending on which point is the first one. I tried the four possibilities in my little method. The response is still a bit confusing!!! I need the exact order.

Hello to all,

I have a problem and wonder if someone can help me. A small example will illustrate the problem:

` def helpme
ents = Sketchup.active_model.entities
a0 = [0, 0, 0]
a1 = [5, 0, 0]
a2 = [5, 3, 0]
a3 = [0, 3, 0]
face = ents.add_face(a0, a1, a2, a3)
for i in 0..3
puts face.vertices[i].position
end

dosomething(face)

end`

There is a difference in the order of the four points shown in the output and the order of points, used in the definition of the face. The outcommented method needs to do something based on the original sequence. A solution or at least a hint would be appreciated.