Measuring distance between two point on a 3d shape

hi all
I have a 3D shape, how can i measure distance between two points?
I cant choose two points on my shape.
I am willing measure distance between a & b points!!
when i click on my shape, it is selected a point out of my shape.

Capture1111

Hello - use the Distance (Analyze menu > Distance) command and object snaps (Quad or Knot looks like it might work here) for this.

-Pascal