lsd_tracker external pose as initial estimate

ext_pose_example.cc

    SE3 frame_to_kf_init = se3FromSim3(curr_tracking_ref_->keyframe->pose->getCamToWorld().inverse() *
                                       sim3FromSE3(pose, 1.0));
    frame_to_kf_init.translation() *= curr_tracking_ref_->keyframe->pose->getCamToWorld().scale();

    SE3 frame_to_kf_upd = tracker_->trackFrame(curr_tracking_ref_.get(),
                                               trackingNewFrame.get(),
                                               frame_to_kf_init);

pose is the external, ground truth pose.