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Re: [gpsd-dev] RFC: GPSd on Android as a system service

From: Adam Serbinski
Subject: Re: [gpsd-dev] RFC: GPSd on Android as a system service
Date: Mon, 06 May 2019 18:29:48 -0400
User-agent: K-9 Mail for Android

>> >> When we have an elevation of -91, and an ss > 0, it means that we
>> >> are actually seeing a signal from that SV, but haven't YET
>> >> almanac or ephemeris for it.
>> >
>> >No. Absolutely nothing in the u-blox doc to support that. Many
>> >have looked for it many times.
>> Do you mean aside from page 285 of the ublox 8 doc in the UBX-NAV-SAT
>> description where it says specifically "Elevation (range: +/-90),
>> unknown if out of range"?
>No. A single negative stataement on -91 is not enough for me. And
>there are multiple ways the u-blox 8 (the only GPS that does this)
>can report elevation and azimuth. They all say similar.

The unknown is part of the field and applies specifically to that field, not to the rest of the packet.

If you don't believe me, you can always check the flags in the same packet. The qualityInd bits will tell you very specifically if there is an actual signal independent of using, you know, the actual signal strength.

>The NMEA doc also says do not pass on invalid data.

Even if the data was invalid, this isnt NMEA.

>I would need a positive statement that says, "-91 means XXX" before
>it would be valid and worth passiings on.
>> In other words, if it transmits a valid CNO, with an elevation that
>> is outside of the range +/-90, then it simply does not know what the
>> elevation is. The details that it does send are valid.
>Pretty circular reasoning. The doc say -91 is invalid, short a
>contradicting official statement of validity, that is good enough for
>gpsd does not pass on invalid data.
>Not worth trying to figure it out as it is not present in other models
>of u-blox, or any other GPS. gpsd is trying to enforce consistency,
>not pass on unknown, and unknowable, data.
>If you really care, go to the u-blox forums and ask. I'll accept any
>answer they (u-blox staff) give as official. Careful with their
>forums, most answers there are unofficial, and often wrong.
>BTW, this is better handled on gpsd-dev, where it has been discussed

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