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how to use ftpx value in road navigation from serial messages

0 votes


I would like to participate to a robot race with Jevois and a RC car.
For your information, here is video about how the road would look like:

I hooked up Jevois (firmware 1.3) to and ESP8266 and can see serial messages on my phone, but the value I get seem to be fTPX and not VP.

Can you please provide information about how fTPX can be used?
It seems to be filtered target point X but is very different from VP value.

Thanks in advance.

asked Aug 13, 2017 in User questions by candas (120 points)

1 Answer

0 votes

(sorry for the delay as we are just back from vacation)

you should use fTPx as it is a kalman-filtered version of the VP that is also converted to standardized coordinates (independent of camera resolution). So you can just use it as the filtered (smoothed) VP location, with the following conventions:

-1000.0 is at the left edge of the image / field of view

0.0 is dead center

1000.0 is at the right edge of the image / field of view

Given the clearly maked black/white lines at the center of the road in your competition, it might be interesting to also try some line detection code? We have not yet implemented any on JeVois but a google search for "visual line following" returns results that might interest you to program your own JeVois module.

answered Aug 18, 2017 by JeVois (46,580 points)
No worries, hope your had a good time :)
In the meantime I experimented more and figured out -1000 to 1000 when trying other modules with arduino sketch.

My problem is that VP green dot looks fine, but ftpx value is different than what I expect.
I tried to upload a video :

Am I misusing the demo ?

Due to lack of time I wanted to test if road navigation module is good enough, but I will definitely try to write a new module.
You are right, the way you are using the demo is correct and indeed just outputting the VP would be better. fTPX was meant to be used directly as steering command but it does not seem to be working well (the original code was also getting odometry and IMU inputs but those are missing here and maybe that is why fTPX is so messed up). I have committed a change to use VP instead, here:


If you are not yet compiling from source, It will be included in the next microSD card update, likely some time later this week.
Thanks a lot for your help, I was getting crazy.
I have no environment to compile the source but will try to setup a virtual machine