Re: [gpsd-users] GPS speed and direction reporting

[Yan Seiner]

Charles Curley wrote:
> On Sun, 16 Oct 2011 10:57:14 -0700
> Yan Seiner <address@hidden> wrote:
>
>   
> > I'm playing with gpsd as a way to record the trips I take...
> > Basically I've hacked gpxlogger to monitor the gps, and every mile or
> > so run a webcam program to take a snapshot of the road.
> >
> > That part works wonderfully.
> >
> > The webcam program also writes the GPS coordinates, time as reported
> > by gpsd, and the direction and speed.
> >     
>
> You wouldn't want to share, would you?
>   

Sure.  The quality of the code is not the best; it needs some work to 
remove cruft and to correctly prototype the functions I added, to make a 
lot of the options I hard-coded user configurable, and to correctly 
attribute the changes (and the bugs I added.  ;-) ).

http://www.seiner.com/cz/gpxlogger.c

Roughly speaking, it initializes the gps, and then enters a loop.  It 
takes a picture every minute or every mile, whichever comes first.  If 
it fails to get a report from the gps for a while, it closes and reopens 
the gps connection (not sure why this is necessary, but it's running on 
a severely constrained access point using OpenWRT, so that could have 
something to do with it.)

Also, fswebcam has the following config file:

device /dev/video0
input 0
delay 1
skip 1
font "LiberationSans-Regular":10
jpeg 95
save /data/pictures/.tmp.jpg

And, if want to use it with OpenWRT, you have to build fswebcam with 
freetype support, and include libfreetype and the font you want to use.

>   
> > it's the last two where that I'm having issues.  gpsd seems to report 
> > about a 5 minute rolling average of speed and direction.  I'm not
> > sure if this as artifact of gpsd or the gps puck I'm using.
> >
> > Is there some way to get gpsd to report a, say, 10 second average?  I 
> > know that the noise in the gps signal will make this more variable.  
> > Right now, gpsd reports a speed of 25MPH a full 6 minutes after I
> > parked the vehicle.....
> >     
>
> You didn't identify your GPS receiver. I have a Globalsat BU-353.
> http://www.usglobalsat.com/p-62-bu-353-w.aspx#images/product/large/62.jpg
> I do not see a lag anything like this. I see a lag in the speed of two
> or three seconds, but that's about it.
>
> I believe all the data are generated by the receiver, and gpsd simply
> reports the data the receiver sends it.
>   
That's what I figured; I was hoping there was a setting I could use.  I 
am using a generic Sirf III puck I got off of ebay about 5 years ago, so 
I guess I should consider myself lucky that it works at all.  :-)

--Yan

--
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