Re: [gpsd-dev] ✘xgps

[Eric S. Raymond]

Gary E. Miller <address@hidden>:
> > 3. I'm not sure I understand the Baidu problem.  Yeah it's weird that
> > the BDGSA sentence is claiming 3D fix with one sat, but maybe the
> > firmware is mixing in pseudoranges from the GNSS birds as well.  I
> > see lots of sats in the skyview, so what is the actual bug here?
> 
> The Skytraq NMEA is reporting that is it using several GNSS and one
> Baidu bird for the 3D fix.  But the gpsd json output only shows the one
> baidu bird as used. Looks like the GPGSA data is getting overwritten by
> the BDGSA data.

OK, I had forgotten how this works.  That will happen, but only on the
first cycle.  In your sample, the first cycle looks like this:

$GPGSV,4,1,13,23,66,310,29,03,65,186,34,26,43,081,27,16,41,124,39*7E
$GPGSV,4,2,13,51,37,160,38,04,37,066,25,09,34,291,10,22,26,156,37*71
$GPGSV,4,3,13,06,19,301,,31,17,052,21,193,11,307,,07,11,232,25*4C
$GPGSV,4,4,13,01,03,202,30*4A
{"class":"SKY","vdop":1.40,"hdop":1.10,"pdop":1.80,"satellites":[{"PRN":23,"el":66,"az":310,"ss":29,"used":false},{"PRN":3,"el":65,"az":186,"ss":34,"used":false},{"PRN":26,"el":43,"az":81,"ss":27,"used":false},{"PRN":16,"el":41,"az":124,"ss":39,"used":false},{"PRN":138,"el":37,"az":160,"ss":38,"used":false},{"PRN":4,"el":37,"az":66,"ss":25,"used":false},{"PRN":9,"el":34,"az":291,"ss":10,"used":false},{"PRN":22,"el":26,"az":156,"ss":37,"used":false},{"PRN":6,"el":19,"az":301,"ss":0,"used":false},{"PRN":31,"el":17,"az":52,"ss":21,"used":false},{"PRN":193,"el":11,"az":307,"ss":0,"used":false},{"PRN":7,"el":11,"az":232,"ss":25,"used":false},{"PRN":1,"el":3,"az":202,"ss":30,"used":false}]}
$BDGSV,1,1,02,214,55,153,40,208,01,299,*67
{"class":"SKY","vdop":1.40,"hdop":1.10,"pdop":1.80,"satellites":[{"PRN":23,"el":66,"az":310,"ss":29,"used":false},{"PRN":3,"el":65,"az":186,"ss":34,"used":false},{"PRN":26,"el":43,"az":81,"ss":27,"used":false},{"PRN":16,"el":41,"az":124,"ss":39,"used":false},{"PRN":138,"el":37,"az":160,"ss":38,"used":false},{"PRN":4,"el":37,"az":66,"ss":25,"used":false},{"PRN":9,"el":34,"az":291,"ss":10,"used":false},{"PRN":22,"el":26,"az":156,"ss":37,"used":false},{"PRN":6,"el":19,"az":301,"ss":0,"used":false},{"PRN":31,"el":17,"az":52,"ss":21,"used":false},{"PRN":193,"el":11,"az":307,"ss":0,"used":false},{"PRN":7,"el":11,"az":232,"ss":25,"used":false},{"PRN":1,"el":3,"az":202,"ss":30,"used":false},{"PRN":214,"el":55,"az":153,"ss":40,"used":true},{"PRN":208,"el":1,"az":299,"ss":0,"used":false}]}

However, when the driver first sees BDGSV it learns  that it has to wait for a
following BDGSV for a complete sat picture.  So the second and all subsequent
cycles are reported like this:

$GPGSV,4,1,13,23,66,310,29,03,65,186,33,26,43,081,27,16,41,124,38*78
$GPGSV,4,2,13,51,37,160,38,04,37,066,25,09,34,291,07,22,26,156,37*77
$GPGSV,4,3,13,06,19,301,,31,17,052,20,193,11,307,,07,11,232,27*4F
$GPGSV,4,4,13,01,03,202,30*4A
$BDGSV,1,1,02,214,55,153,40,208,01,299,*67
{"class":"SKY","vdop":1.40,"hdop":1.10,"pdop":1.80,"satellites":[{"PRN":23,"el":66,"az":310,"ss":29,"used":false},{"PRN":3,"el":65,"az":186,"ss":33,"used":false},{"PRN":26,"el":43,"az":81,"ss":27,"used":false},{"PRN":16,"el":41,"az":124,"ss":38,"used":false},{"PRN":138,"el":37,"az":160,"ss":38,"used":false},{"PRN":4,"el":37,"az":66,"ss":25,"used":false},{"PRN":9,"el":34,"az":291,"ss":7,"used":false},{"PRN":22,"el":26,"az":156,"ss":37,"used":false},{"PRN":6,"el":19,"az":301,"ss":0,"used":false},{"PRN":31,"el":17,"az":52,"ss":20,"used":false},{"PRN":193,"el":11,"az":307,"ss":0,"used":false},{"PRN":7,"el":11,"az":232,"ss":27,"used":false},{"PRN":1,"el":3,"az":202,"ss":30,"used":false},{"PRN":214,"el":55,"az":153,"ss":40,"used":true},{"PRN":208,"el":1,"az":299,"ss":0,"used":false}]}

GSVs are reported once per five cycles, so the the xgps sat display will
straighten itself out ten seconds in.
-- 
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>

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