Hi guys I still couldn't figure this out so I am going ask again. Hopefully someone can enlighten me. :) I have this 3D model of a crumpled page made up many triangles. This is constructed by using a 3D camera which will scan the document and save the structure in wavefront file. After loading it, I need to to flatten this 3D model to produce a flat shape. This requires me doing shape deformations that obey physical laws. Currently I am using gravity as external force to push down the structure and a mass spring system(internal force) to model the rigidity. Since each point is in 3D space, the force is represent as Fx, Fy, Fz and similarly for the position and velocity. However with gravity, I am only able to move the masses vertically downwards since it only affect Fz. As such I cannot conserve total surface area. I understand that as the masses move downwards due to gravity, the spring should be compressed or stretched. However, I am not sure how to calculate this for Fx and Fy since there is no change in distance as it only affects the z axis. Is it a flaw in calculation to resolve the force in 3 directions? Please refer to the link below for illustration: http://www.cs.ust.hk/~brown/text_research.htm Thanks for reading.

The neighbords of your vertices are the ones exerting force. They exert force as 3D vectors. You can not separate this in the three main axes -- you have to treat them as 3D vectors, and sum/average them like that.

Quote: Original post by hplus0603

The neighbords of your vertices are the ones exerting force. They exert force as 3D vectors. You can not separate this in the three main axes -- you have to treat them as 3D vectors, and sum/average them like that.

Do you mean that for each vertex, the spring force Fx = Fy = Fy?