Method num_cameras

examples/bal_problem.h:70–70

  int camera_block_size()      const { return use_quaternions_ ? 10 : 9; }
  int point_block_size()       const { return 3;                         }
  int num_cameras()            const { return num_cameras_;              }
  int num_points()             const { return num_points_;               }
  int num_observations()       const { return num_observations_;         }
  int num_parameters()         const { return num_parameters_;           }