Visibility of points on an edge - occlusion

Hi all,

I am working on a definition that should provide me with the number of points on a curve that can be seen from a distant point while being obstructed by a surface. I am using the occlusion component for this, but it seems it's not working properly. It might that I'm abusing the component for the wrong purpose or (more likely) that the vector definition is off, but I don't how to fix the definition.

I've attached a file that hopefully explains the problem. I was expecting that the number of rays that were occluded to be the same as the total number of rays. But it appears not to be so. However, if I move the mesh horizontally or vertically, the number changes.

Hope you can help.

Regards,

Roel.