Bundle adjustment in rpc mode and correct rotation matrix

[lionlai1989]

Hi, the team of sat-bundleadjus:
Firstly, it's an awesome project. I have a question of why the rotation vector and translation vector are set to zero vector when in RPC model and the goal is to correct rotation matrix. The default camera mode is rpc and the default camera parameter to optimize is rotation matrix.

1. In bundle_adjust/ba_params.py, it's setting rotation and translation vector to zero vector.
2. The parameter to be optimized is the first three element of self.cam_params which is the rotation vector. And this to be optimized parameter is stored in self.params_opt which will be used as the variable to be optimized.
3. In bundle_adjust.ba_core.run_ba_optimization, it reads the value of vars_init = p.params_opt.copy(), and then use this as the initial guess to feed into the solver.
   My question is that since the cam_params is a 9-vector, wouldn't the solver will solve all the 9-vector instead of only the rotation matrix?

Best,