Re: Strangeness with speed

[Florian Kiera]

Hey Владимир,

the reason the 2nd TPV message returns speed 0 is because you didnt move 
an inch compared to the previous point. Which speed value do you expect? 
"null" is entirely wrong in this situation as its possible to calculate 
a speed value with the points you have (speed = (p2-p1) / (t2-t1); speed 
= ((61.079583333, 28.254500000) - (61.079583333, 28.254500000)) / 
(11:48:13.000-13:46:18.000); speed = 0/(11:48:13.000-13:46:18.000) = 0)

Besides, its interesting that gpsd is calculating any speed at all with 
the "sentences.nmea" file you gave us, as multiple NMEA sentences are 
from the exact same time. (You're at multiple places at the same time? 
How can that result in a speed value when the time difference is 0? 
(division through 0 returns a valid speed value?))
I simply downloaded the "sentences.nmea" file and used "cat 
sentences.nmea | gpsdecode > test.txt". May I have used it wrong. Wrong 
and wrong might resulted in even more wrong? Might be my bad.

By the way as Gary already mentioned the file you gave us is different 
to the file you used to produce your outputs... you may want to send 
your original file or else nobody can help you with the problem you have 
with your original file.

Regards Florian

test.txt would be to big (672KB) so I quartered the file.

Am 14.02.22 um 15:51 schrieb Владимир Калачихин:
> Hi all and Gary. I have an underground knock.
>
> I have the NMEA file (included).
> I created this file on my app by filtering RMC and GGA sentences and 
> changing the time.
>
> I play this file in gpsfeed, and gpsd understands him perfectly. As 
> result, gpsd return the following:
> {"class":"TPV","device":"tcp://localhost:2222","mode":3,"time":"2022-02-14T11:46:18.000Z","ept":0.005,"lat":61.079016667,"lon":28.256983333,"altHAE":36.440,"altMSL":49.870,"alt":49.870,"track":283.8300,"magtrack":10.7967,"magvar":10.8,"speed":2.212,"geoidSep":0.000,"eph":0.000} 
>
>
> The same result is if I play this file in my app without any changes 
> in data.
>
> But if I during playback changed the time in sentences to now - gpsd 
> returns two differents TPV:
>
> {"class":"TPV","device":"tcp://localhost:2222","mode":3,"time":"2022-02-14T11:46:18.000Z","ept":0.005,"lat":61.079583333,"lon":28.254500000,"track":296.0900,"magtrack":306.8855,"magvar":10.8,"speed":2.531,"geoidSep":16.832,"eph":0.000} 
>
> {"class":"TPV","device":"tcp://localhost:2222","mode":3,"time":"2022-02-14T13:48:13.000Z","ept":0.005,"lat":61.079583333,"lon":28.254500000,"altHAE":54.300,"altMSL":54.300,"alt":54.300,"magvar":10.8,"speed":0.000,"geoidSep":0.000,"eph":0.000} 
>
>
> one of these has speed == 0
>
> Why is it that?
> Is it the time value something special for gpsg?
> Why speed == 0 instead null?
--
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Florian Kiera               Tel:    (0385) 3993 93 58
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test.txt
Description: Text document