   server-side collition detection
  it's quite general question: how to implement server-side collision detection for NPC movement and PC movement verification, for MMORGP.Possible options: to implement it from scratch or to use some physic engine, e.g. Bullet, ODE or even PhysX. Server is running on Linux.In case of implementing it from scratch: what is typical approach? multi-layer heighmap? how labor-intensive is this task? In case of physic engine: is it effective solution for large worlds? Isn't time spend to become familiar with it equal to time required to implement it from scratch?thanks in advance for sharing your opinion   