Is there someone who can tell me about local coordinates and global coordinates. What is the difference?
I have reported down a piece of code of Yasim\Model.cpp with some questions attached (**....**) // Returns a unit "down" vector for the ground in out, and the // distance from the local origin to the ground as the return value. // So for a given position V, "dist - (V dot out)" will be the height // AGL. **what is height AGL?** float Model::localGround(State* s, float* out) { // Get the ground's "down" vector, this can be in floats, because // we don't need positioning accuracy. The direction has plenty // of accuracy after truncation. out[0] = -(float)_ground[0]; **why is it inverted?** out[1] = -(float)_ground[1]; out[2] = -(float)_ground[2]; Math::vmul33(s->orient, out, out); // The distance from the ground to the Aircraft's origin: ** what is the meaning of this operation, what is _ground[3]?** double dist = (s->pos[0]*_ground[0] + s->pos[1]*_ground[1] + s->pos[2]*_ground[2] - _ground[3]); return (float)dist; } // Get a ground plane in local coordinates. The first three // elements are the normal vector (**where is the origin of this vector?**), the final one is the distance // from the local origin along that vector to the ground plane // (negative for objects "above" the ground) **Why negative?** float ground[4]; ground[3] = localGround(s, ground); float alt = Math::abs(ground[3]); _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel