Quote - "the intersection/bounds checking code doesn't really distinguish the direction of  the ray being cast" - Are you suggesting that it needs to?  Or is this a moot point once the region code is repaired?

Possibly moot, once repaired, but I need to think about that more.

Quote - "if you're not using the  center version, then the direction vector ('ang') needed is just the vertex normal" - So the normal vector itself serves in place of the line?  Nothing needs to replace the removed calculations?  (I've never been able to puzzle out how a vector can be equivalent to a point in some regards, yet possess direction or magnitude....  Cage is a bit slow.)

Yeah, it's not always clear whether a 'vector' is actually being used as a vertex/point or as a direction/normal vector...

To cast a ray, you need 2 things - a starting point and a direction vector.  To get the direction vector (for a line), you subtract the starting point from the ending point and then 'normalize' the result - divide each axis by the magnitude (distance/length) of that line - this produces what's commonly known as a 'unit vector' (Normals are unit vectors).

Unit vector's have the defining characteristic that thier 'length' is 1.0, so they describe a direction only.  If you want a line starting from vertex startV, with a length/distance/magnitude of length along the direction/unit vector angle, you can get the end point of the line with:

endV = startV + (length * angle)

So, if we look back at that code, you can see what's ultimately happening with 'ang' down below there a bit... 

point = [(ang[0]*intersect)+v[0],(ang[1]*intersect)+v[1],(ang[2]*intersect)+v[2]]

...v is the startV point of the line, intersect is actually the length/distance of the line and ang is the unit/direction vector being used to come up with point, which is the endV point of the line.

In the case of casting a ray out from the vertex, the code is doing some redundant stuff to produce what is essentially the normal for that vertex...

v = coord_list(geom2,vi) # get vertex
vn = normals_list(geom2,vi) # get normal
vnv = vecadd(v,vn) # add normal to vertex (effectively the end point of a line from v to vnv along it's normal, with a length of 1.0)
dist = point_distance(v,vnv) # now compute distance of that line (it'll be 1.0)
ang = [(v[0]-vnv[0])/dist,(v[1]-vnv[1])/dist,(v[2]-vnv[2])/dist] # and 'normalize' the vector by dividing each axis by the distance

...and voila! - you're back where you started from - with the normal for that vertex :).

If you are casting the ray out from the center of the mesh, then you're not actually using the vertex's normal, so you create a new angle/vector starting at the center and just passing through the vertex.  You can see similar code being used to determine that angle.

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