Navdata framerate

[jocacace]

Hi Guys,

I have a question about the navdata of the robot that come with the "Update" function. What is the framerate of the telemetry data? I am using the code but the update function provide me updated data at very slow frequency (something like 0.5 Hz)... In addition, do you know if there is a sdk documentation where all the kind of provided data are listed?

P.s I am using ubuntu 12.04 to run the code.

Thank you a lot for your support!

[m3d]

The telemetry data should be at 5Hz while video could be up-to 30Hz (typically you will get only first I-frame and say 10 P-frames). Do you have a piece of code I could look at? Do you use video?

[jocacace]

Hi m3d, thank you for your reply. Actually I found a bug in my code, and yes, I can see telemetry data at 5Hz, even thought I am not able to read the complete data set ( for instance seems that I am not receiving battery or state data, but maybe is because I am testing the code without taking off, only using bebop in an Idle state).

My big problem now is with the image... I read the issue #3 , I am working with Linux but I am not able to use cvideo and I decided to try to read the bebop image. Even thought I just put a print into the image callback (so don't handle the frame image at all), seems that I receive a new frame every 1 second. Maybe I haven't understand good the image transmission protocol or the difference between I-frame and P-frame...

Here is the code that I am using to acquire the data (note that I started from "demo.py" program):

def videoCallback( frame, robot=None, debug=False ):
    if frame:
        print strftime("
![screenshot - 04122015 - 09 33 12 pm](https://cloud.githubusercontent.com/assets/10219563/7107163/d29e2e88-e15b-11e4-9be8-0109003ce5bb.png)
%S", gmtime()), " new image"

def demo( drone ):
    print "demo ..."
    drone.videoCbk = videoCallback
    drone.videoEnable()
    try:
        drone.trim()
        while 1:
            drone.update( cmd=None )

    except ManualControlException, e:
        print
        print "ManualControlException"
        if drone.flyingState is None or drone.flyingState == 1: # taking off
            drone.emergency()
        drone.land()

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print __doc__
        sys.exit(2)
    metalog=None
    if len(sys.argv) > 2:
        metalog = MetaLog( filename=sys.argv[2] )
    if len(sys.argv) > 3 and sys.argv[3] == 'F':
        disableAsserts()

    drone = Bebop( metalog=metalog )
    demo( drone )
    print "Battery:", drone.battery

And here is an output (via shell) of the program:

As you can see, "new image" should be print every time a new image has been acquired... and it's printed each second.

Any suggestion? There is something wrong in my code?

Thank you

[m3d]

OK, first of all battery and many other values are reported only on change. I wanted to add ARCOMMANDS_ID_COMMON_SETTINGS_CMD_ALLSETTINGS, but I do not have Bebop now, i.e. how to test it. In your case is 1Hz video expected. I moved video assembly into Bebop class, which means that also parameter if to use only I-frame or also P-frames is now part of Bebop constructor. Use drone = Bebop( metalog=metalog, onlyIFrames=False ).

The motivation for I-frames only is that you can read/display them with OpenCV via temporary file and it is mostly sufficient to "get started" with your image processing.

[jocacace]

Perfect, now everything is more clear! Thank you a lot for your explanation... so, sorry for my other question, but I am quite new of image decoding and stuff like this... This mean that if I want a complete image frame I have to wait 1 second. Is more fast the decoding of the image If I use something like cvideo?

In the original sdk there is a source code example that show how to display the on-board image using mplayer, and in that way seems more fast (like in the android app), but I am not able to understand how to use the acquired image and to implement my algorithm I need an image at leas at 5Hz...

[m3d]

You may try to replay automatically logged video packets via python ./play.py logs/navdata_150412_213255.log If you need at least 5Hz you have to deal with P-frames (there are typically 1 I-frame and 29 P-frames per second). You can probably try mplayer with https://github.com/robotika/katarina/blob/master/samples/video2stdout.py but make sure you redirect the stdout to pipe.

[jocacace]

Just to be sure of the meaning (before close this issue :) )... with python ./play.py logs/navdata_150412_213255.log I can replay the video a posteriori, not while flying, right? I want to implement a visual servoing algorithm, similar that one implemented in demo.py example, where the drone should follow the red cup...

[m3d]

Right I will try to find some alternative for cvideo or make it working under Linux. p.s. I would use https://github.com/robotika/katarina/blob/master/behaviors/navbox.py as more advanced reference, because it uses multiprocessing and the image processing results are automatically logged

[jocacace]

Ok, again thank you! In addition I will try to use cvideo on linux, or I will move on Windows!