re surface normal orientations in pscti aqe travis csd harris com srp travis csd harris com stephen pietrowicz writes how do you go about orienting all normals in the same direction given a set of points edges and faces this algorithm works well for me algorithm to attempt to find outward facing normals first mark all faces as unknown then create an edge dictionary that allows you to find all of the faces sharing a given edge where an edge is two integers representing the two shared vertices pick an arbitrary face and mark it counter clockwise using the edge dictionary orient all surrounding faces based on the orientation of this face and recurse for all surrounding faces consistently orienting the entire surface find the average of the vertices in this surface using that point calculate a volume measurement taking into account the face s orientation if the volume turns out to be positive assume the faces are oriented correctly if it is negative reverse their orientations mark them clockwise if any faces are still unknown after this choose another face and go through the algorithm again at the end faces marked clockwise must have their indices reversed before facet normals are found note if you are running on silicon graphics machines and buy the iris inventor d toolkit developers package you have the source to this algorithm see usr src inventor tools ivnorm if you re not sorry i can t give out the source and even if i could it relies heavily on inventor gavin gavin sgi com
