[vmtk-users] vmtkbifurcationvectors - Computation of bifurcation points

[Carlos A. B. <car...@gm...>]

Hi vmtk community,
I'm trying to understand the output of the vmtkbifurcationvectors filter.
After following the tutorial I successfully compute the bifurcation
vectors, but I would like to know a litle more about the output,

Suppose I have an Y shaped tree, then the filter gives me a polydata with 3
points (P1,P2,P3), I understand each point is associated to an specific
artery (through the GroupId array), and all three belong to the same
bifurcation (BifurcationGroupId). I can also know the direction by querying
the BifurcationVectorsOrientation array, and angles with the corresponding
arrays. What I found difficult to understand is how this 3 points are
calculated, because all angles and in/out vectors depend on them, so I try
to read he source code first. Please, correct-me if i miss-understood
something:

First the bifurcation is identify,
Then, for each cell i (arterial segment) involved in the bifurcation
    The orientation (in/out) is determined
    The subset of cell points at the begin and end of the segment are
determined (by the radius)
    A weighted averaged is used for computing two points (for the beginning
and end  of the cell) which are called averageTouchingPoint and
averageLastPoint
   Then, depending on the orientation, the bifurcation vector of the cell
is computed by subtracting this points, and one of them is used as the
bifurcation point Pi.


Then, if that is the way of computing P1, P2 and P3, that explains why they
usually don't touch the associated centerline, for example for a C shaped
branch, the bifurcation point will be inside the C, right?

I was thinking also that the bifurcation plane centroid is never used for
computing the bifurcation point nor the bifurcation vectors of each cell,
correct?
For example the bifurcation point could be set to the averageTouchingPoint
and the bifurcation vector computed as bifurcationCentroid -
averageTouchingPoint.

Well Thank you very match for developing VMTK, and i hope you can help me
find out the exact way the bifurcation points are computed.
Regards
Carlos