# Optitrack to RTF integration **URL:** \ **Category:** PX4 Autopilot\ **Created:** [February 10, 2019, 12:14am UTC](https://discuss.px4.io/t/optitrack-to-rtf-integration/9555 "2019-02-10T00:14:58Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![hooverryan](https://discuss.px4.io/user_avatar/discuss.px4.io/hooverryan/32/2960_2.png) [@hooverryan](https://discuss.px4.io/u/hooverryan)\ **Post date:** [February 10, 2019, 12:14am UTC](https://discuss.px4.io/t/optitrack-to-rtf-integration/9555/1 "2019-02-10T00:14:58Z")
I am trying to get my Intel RTF done to fly using position information from an Optitrack system. Ultimately I would like to fly using offboard commands from my laptop in an area with no GPS. First some system information. PX4 version: 1.8.2 Motive version: 1.7.3 Computer OS: Ubuntu 16.04 Drone OS: Ubuntu 16.04 ROS version: kinetic I am using the vrpn\_client\_ros package to stream data from the Optitrack system to my laptop. That appears to be working as I can echo the /vrpn\_client\_node/robot1/pose topic to the screen and it updates as I move the drone. I tried to start mavros on my laptop using the following command `roslaunch mavros px4.launch fcu_url:="udp://:14540@192.168.8.1:14557"` I am certain of the IP address (192.168.8.1), but not about the port, or the syntax. I assume this would connect to the flight controller, and if it could subscribe to the data stream from Optitrack, I would be set. From the I need to remap the /vrpn\_client\_node/robot1/pose to /mavros/vision\_pose/pose using `rosrun topic_tools relay /vrpn_client_node/robot1/pose /mavros/vision_pose/pose` however, the position shown in QGroundcontrol does not update. Any ideas what I am doing wrong? ---
**Author:** ![hooverryan](https://discuss.px4.io/user_avatar/discuss.px4.io/hooverryan/32/2960_2.png) [@hooverryan](https://discuss.px4.io/u/hooverryan)\ **Post date:** [February 11, 2019, 12:46pm UTC](https://discuss.px4.io/t/optitrack-to-rtf-integration/9555/2 "2019-02-11T12:46:20Z")
I found part of the problem. The connection string to start Mavros was incorrect. `roslaunch mavros px4.launch fcu_url:="tcp://192.168.8.1:5760"` Now the problem is the coordinate frame is incorrect from the vrpn\_client\_mode topic. Following the instructions from [External Position Estimation](http://dev.px4.io/en/ros/external_position_estimation.html), I was to flip the Up Axis in the Motive software. However, my version of the Motive software doesn’t have that option (1.7.3), or at least I have been unable to find that option. Any ideas? I’m planning on transitioning to mocap\_optitrack, as the [External Position Estimation](http://dev.px4.io/en/ros/external_position_estimation.html) page suggests it already has the coordinate frame modified. ---
**Author:** ![charles-blouin](https://discuss.px4.io/user_avatar/discuss.px4.io/charles-blouin/32/3932_2.png) [@charles-blouin](https://discuss.px4.io/u/charles-blouin)\ **Post date:** [February 11, 2019, 8:04pm UTC](https://discuss.px4.io/t/optitrack-to-rtf-integration/9555/3 "2019-02-11T20:04:06Z")
I have not seen that issue directly, but you could write a ROS node that corrects the data. If you are not using ROS elsewhere in your project, you could forward the UDP packets using a script on your companion computer. This is what I have done with my mocap system and drone. ROS is great for robotics, but it can add a bit of complexity if only packet forwarding is required. Edit: I mean that you could run a script on the companion computer that listens for the pose packets from the mocap system and rebroadcast them as mavlink messages to the drone. ---
**Author:** ![hooverryan](https://discuss.px4.io/user_avatar/discuss.px4.io/hooverryan/32/2960_2.png) [@hooverryan](https://discuss.px4.io/u/hooverryan)\ **Post date:** [February 12, 2019, 2:36pm UTC](https://discuss.px4.io/t/optitrack-to-rtf-integration/9555/4 "2019-02-12T14:36:47Z")
I modifed the code in the vrpn\_client\_ros package according to the instructions in [External Position Estimation](http://dev.px4.io/en/ros/external_position_estimation.html). I’ll reproduce them here. > If `x_{mav}`, `y_{mav}` and `z_{mav}` are the coordinates that are sent through MAVLink as position feedback, then we obtain: > ``` > x_{mav} = x_{mocap} > y_{mav} = z_{mocap} > z_{mav} = - y_{mocap} > > ``` > > Regarding the orientation, keep the scalar part w of the quaternion the same and swap the vector part x, y and z in the same way. You can apply this trick with every system - if you need to obtain a NED frame, look at your MoCap output and swap axis accordingly. That pretty much took care of it. Now the RTF has the correct position information.