# Fiducial Follow error

**URL:** <https://forum.ubiquityrobotics.com/t/fiducial-follow-error/117>\
**Category:** General Questions\
**Created:** [August 23, 2018, 11:55pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-follow-error/117 "2018-08-23T23:55:11Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![acmueller](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/a/74df32/32.png) [@acmueller](https://forum.ubiquityrobotics.com/u/acmueller)\
**Post date:** [August 23, 2018, 11:55pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-follow-error/117/1 "2018-08-23T23:55:11Z")

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I find that the magnitude does not respond to the target 49. I performed the following test after ssh to the robot.  
raspistill -o test.jpg  
Took a look at the test.jpg and it showed nothing unusual. I believe the raspberry pi cameral is functioning as expected

As instructed I ran the command

sudo systemctl stop magni-base

and then the command

roslaunch magni\_demos fiducial\_follow.launch

As soon as I placed the default target “49” in front of the camera the output came to the screen which I attempted to capture partially before killing the  
It appears that the Fid 49 is actually identified but there appears to be an error related to “base\_link” not existing

=========================================

traceback (most recent call last):  
File “/home/ubuntu/catkin\_ws/src/demos/fiducial\_follow/nodes/follow.py”, line 151, in newTf  
tf = self.tfBuffer.lookup\_transform(“base\_link”, self.target\_fiducial, imageTime)  
File “/opt/ros/kinetic/lib/python2.7/dist-packages/tf2\_ros/buffer.py”, line 87, in lookup\_transform  
return self.lookup\_transform\_core(target\_frame, source\_frame, time)  
LookupException: “base\_link” passed to lookupTransform argument target\_frame does not exist.  
Could not get tf for fid49  
[INFO] [978312395.092011143]: Got image 422  
[INFO] [978312395.113678904]: Detected 1 markers  
[INFO] [978312395.115822497]: Detected id 49 T -0.05 -0.11 0.66 R 0.63 3.04 0.09  
[INFO] [978312395.115943851]: angle 3.102972 axis 0.202755 0.978818 0.028400  
978312395066530154 978312395117108941

* * *

Fid 49 -0.046404 -0.106144 0.657721 0.202717 0.978635 0.028395 0.019309

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<div class="post-metadata">

**Author:** ![rohbotics](https://forum.ubiquityrobotics.com/user_avatar/forum.ubiquityrobotics.com/rohbotics/32/222_2.png) [@rohbotics](https://forum.ubiquityrobotics.com/u/rohbotics)\
**Post date:** [August 25, 2018, 8:21pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-follow-error/117/2 "2018-08-25T20:21:45Z")

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Try running it again after rebooting,  
but this time don’t run `sudo systemctl stop magni-base`.

This command is longer needed, and the documentation needs to be updated.

Rohan

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<div class="post-metadata">

**Author:** ![acmueller](https://forum.ubiquityrobotics.com/letter_avatar_proxy/v4/letter/a/74df32/32.png) [@acmueller](https://forum.ubiquityrobotics.com/u/acmueller)\
**Post date:** [August 26, 2018, 6:39pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-follow-error/117/3 "2018-08-26T18:39:22Z")

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Thanks Rohan that sorted out the problem!  
I took the mangi for a little spin around the house and it performed as advertised. Is there a way to gracefully stop the process other than control-c (or via a hardware reset button)? Also once launched, does the raspberry pi need to be connected wirelessly to the ubuntu workstation?

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<div class="post-metadata">

**Author:** ![rohbotics](https://forum.ubiquityrobotics.com/user_avatar/forum.ubiquityrobotics.com/rohbotics/32/222_2.png) [@rohbotics](https://forum.ubiquityrobotics.com/u/rohbotics)\
**Post date:** [August 26, 2018, 7:05pm UTC](https://forum.ubiquityrobotics.com/t/fiducial-follow-error/117/4 "2018-08-26T19:05:46Z")

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Great! Documentation has been updated.

“Ctrl-C” is the graceful shutdown 🙂

They don’t need to remain connected, but if the ssh connection drops, the process will die.

To prevent this, before launching run `screen`, and then run the launch. Then you can detach from this session with “Ctrl-A” followed by “D”.

To reattach (to analyze output or gracefully stop) run screen -r.

Rohan