Find angle between two different objects from intersection of the lines

问题

I have some knee segmentation images here is an example

My goals are:

1. Generate green colored dot in each object automatically.
2. Create a line which is across each object and black colored dot from intersection of cross sign automatically.
3. find the angle from intersection of these lines.

Illustration of my goals is done here

I've created cross sign in each objects (femur and tibia), but the problem is I don't know what to do to achieve the next steps.

Please, I need your help. MATLAB or C implementation will be pleasure. Thanks

回答1:

your angles are very distorted because you can not determine the cross position precise enough and also if the bone is slightly deformed or aliased you got low precision output.

I would instead:

1. cast horizontal scan lines (yellow)
2. find first (red) and last (green) bone point along it
   • first point by scanning from left
   • last point by scanning from right (to avoid problems with fractures or segmentation gaps)
3. compute mid point between them (blue/magenta)
   • ignore too close red/green points by some treshold
4. regress lines per each bone midpoints
5. compute angle
   • by atan2,atanxy
   • or by acos(dot(linedir1,linedir2)) if angles are constrained enough

[Notes]

• to increase accuracy you can ignore too distant start/endpoints too
• and this also flags that next bone is starting

来源：https://stackoverflow.com/questions/30462831/find-angle-between-two-different-objects-from-intersection-of-the-lines