Hi Shawl, >my question is that i want to select a point of the scene as the rotation center of the trackball manipulator . i know how to pick objects ,
I will not answer your question, but will say an approach, which I can think of in principle 2D to 3D an approach is described say here ( just skip this is directx ) http://www.mvps.org/directx/articles/rayproj.htm http://www.mvps.org/directx/articles/improved_ray_picking.htm ( there are few examples to pick objects ), but in case of cloud you most probably will need an octree, which has all points, then you intersect octree cubes and in the smallest cube which is intersected - if theris one point - select it, if there are few = select nearest point to the intersecting line ( see somewhere point line distance ) Regards Sergey
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