What do 'nx' 'ny' and 'nz' mean in exported ply model?


Hello everyone, I’m trying to using the PLY model exported by “Skanect”(in Windows platform), like draw the object scanned using OpenGL or something. And there are 9 elements for each vertex: x, y, z,(the coordinates of each vertex); red, green, blue(color); and nx, ny, nz, with which I’m little confused. Do they mean the direction of each vertex? Are they pointing to the outside of the surface? And, the most important is, how they are calculated?
Thank you very much!



[nx ny nz] is a normal vector associated to the vertex. Its direction is orthogonal to the surface, pointing out, and they are computed during the 3D reconstruction, so they are more accurate than trying to recompute them from the final mesh triangle faces.