Support for SirF Binary GPS Sentences

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Support for SirF Binary GPS Sentences

Postby Madhadder » Fri May 14, 2004 8:18 am

With alot of people looking to use or are already using GPS's that use
the SirF Binary format, perhaps it's time that NS/MS start to supports
this protocol.

Yes these GPS's can also out NMEA, with modification but so can the Garmin
GPS's and NS/MS support Garmin Binary also...

What do Ya'll think..

If a Referenc Manual is needed there is one HERE (PDF)

And HERE (PDF) is another
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Postby lincomatic » Fri May 14, 2004 9:41 am

Madhadder wrote:With alot of people looking to use or are already using GPS's that use
the SirF Binary format, perhaps it's time that NS/MS start to supports
this protocol.

Yes these GPS's can also out NMEA, with modification but so can the Garmin
GPS's and NS/MS support Garmin Binary also...

What do Ya'll think..

If a Referenc Manual is needed there is one HERE (PDF)

And HERE (PDF) is another


having worked w/ SiRF binary protocol myself, i have to say that it's a pretty big effort to support it. the problem is that the SiRF binary data are a lot more "raw" then NMEA ... you have to convert X/Y/Z to lat/lon/altitude among other things, and there is a lot of messy work involved.
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Postby Madhadder » Fri May 14, 2004 1:52 pm

How does it compare to Garmin Binary?
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Postby Dutch » Fri May 14, 2004 2:22 pm

Just some simple questions :

WHY should NS support Sirf binary ?

What are the benefits of Sirf Binary over NMEA considering the usage of NS ?

AFAIK all Sirf based consumer GPS's support NMEA output, and there are even Sirf based GPS's which don't output Sirf Binary (such as the Holux GM-270Ultra CF card GPS, which only outputs NMEA, eventhough it's a Sirf II with Sirf Xtrac...)

IMHO it would be time better spent by Marius to work on the WiFi aspect, instead of getting NS to support unnecessary things...

Just my 0.02€'s worth...

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Postby lincomatic » Fri May 14, 2004 2:36 pm

Madhadder wrote:How does it compare to Garmin Binary?


don't know anything about garmin binary...but if i recall correctly, garmin binary processes the data into the kinds of units are easier to deal with (lat/lon/altitude)... maybe someone w/ more knowledge can correct me if i'm wrong.
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Postby Madhadder » Sat May 15, 2004 1:16 am

Dutch wrote:Just some simple questions :

WHY should NS support Sirf binary ?

What are the benefits of Sirf Binary over NMEA considering the usage of NS ?

AFAIK all Sirf based consumer GPS's support NMEA output, and there are even Sirf based GPS's which don't output Sirf Binary (such as the Holux GM-270Ultra CF card GPS, which only outputs NMEA, eventhough it's a Sirf II with Sirf Xtrac...)

IMHO it would be time better spent by Marius to work on the WiFi aspect, instead of getting NS to support unnecessary things...

Dutch


What are the benefits of using Garmin Binary???
I don't know either, but NS/MS also support them, even though garmin
GPS's ALSO support NMEA out...

This is the thing about "Suggestions", they don't have to added unless
Marius wants...
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Postby sparafina » Sat May 15, 2004 5:58 am

Back in the day, I worked with Rockwell binary. I think the advantage was faster position fixes than NMEA. Of course the amount of processing power that they can pack on a chip these days probably makes that moot.

This OT but I was reading about the new fequencies that the Gallileo system will use and it is possible in the near future (2-4 years) that GPS will work inside.
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Postby lincomatic » Sat May 15, 2004 8:17 am

sparafina wrote:Back in the day, I worked with Rockwell binary. I think the advantage was faster position fixes than NMEA. Of course the amount of processing power that they can pack on a chip these days probably makes that moot.

This OT but I was reading about the new fequencies that the Gallileo system will use and it is possible in the near future (2-4 years) that GPS will work inside.


right, that's why i was interested in SiRF binary...but w/ SiRF binary all you're doing is offloading more processing the the host.
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Postby Dutch » Sat May 15, 2004 10:21 am

AFAIK most if not all Sirf based GPS units have a messagerate of 1 hz (once pr. second) in NMEA mode. And we all know that the faster we go, the fewer AP we'll probably find. If we say that the max speed we use when wardriving is app. 50 Km/h that update rate would mean we would move 13,8 meters between each position update.

Do we need more precision than that ?

As Lincomatic correctly say, by using Sirf binary, we suddenly move the Lat/Lon format calculation of the position from the GPS to the computer.
Instead of just parsing the clear text output of the GGA or GGL NMEA messages, NS have to parse the binary data AND calculate the Lat/Lon from X/Y/Z coordinates.

Is that worth it to get positionupdates every half second meaning our max moved distance is now 6,9 meters at the 50 Km/h speed ?
BTW I haven't checked if the 1 hz update frequency limit is lifted when in Sirf binary mode, so don't even know if a faster update rate is available.

Just my 0.02€'s worth...

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Postby sparafina » Sat May 15, 2004 10:59 am

Dutch wrote:AFAIK most if not all Sirf based GPS units have a messagerate of 1 hz (once pr. second) in NMEA mode. And we all know that the faster we go, the fewer AP we'll probably find. If we say that the max speed we use when wardriving is app. 50 Km/h that update rate would mean we would move 13,8 meters between each position update.

Do we need more precision than that ?


I think you just made the point why we need more position fixes. It is accepted practice (never tested to my knowledge) that 30 mph. That means you are moving .5 miles in one minute. Keeping in mind that consumer GPS accuracy (+-15 meters) is based on fixes acquired from a fixed position, I guestimate that moving adds about 10-15 meters of error to the position fix. So the more position fixes you have, the more accurately you can locate AP's.


As Lincomatic correctly say, by using Sirf binary, we suddenly move the Lat/Lon format calculation of the position from the GPS to the computer.
Instead of just parsing the clear text output of the GGA or GGL NMEA messages, NS have to parse the binary data AND calculate the Lat/Lon from X/Y/Z coordinates.


I think this is incorrect, the position fixes are still calculated by the receiver's firmware. You are just moving parsing the binary stream to the program.

Is that worth it to get positionupdates every half second meaning our max moved distance is now 6,9 meters at the 50 Km/h speed ?


This really depends on what you want the tool to do. If you are using it for "fox and hound" type location in a moving vehicle then maybe. For general purposes I don't think its necessary to have sub-second position fixes. Then again, I like having as much data as I possibly can get, but that's just me.

Personally, I think XML output is a more important feature than supporting binary GPS formats.
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Postby lincomatic » Sat May 15, 2004 2:40 pm

sparafina wrote:I think this is incorrect, the position fixes are still calculated by the receiver's firmware. You are just moving parsing the binary stream to the program.


i wasn't saying that position fixes aren't calculated by the receiver in SiRF mode.... just that it needs further processing to get lat/lon out of it.

take a look @ the SiRF binary protocol. the only positional info you can get out of it is in X/Y/Z (ECEF) format.... Message ID. 2: Measure Navigation Data Out.
so the program has to convert that to get L/L/A. i am not a GIS person ... it took one of my engineers several weeks of work to figure out how to to that. here is an example of the complexity involved:

http://www.eas.purdue.edu/~calais/teaching/eas591t/EAS_591T_2003_lab_2.htm

for my own application we also needed to extract other stuff like velocity & heading...so for NS it would be a lot easier. but i think we both agree that it's really not worth Marius's effort to write a bunch of binary parsing and hairy arithmetic routines just because someone doesn't feel like switching their GPS to NMEA mode.
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Postby sparafina » Sat May 15, 2004 7:17 pm

lincomatic wrote:i wasn't saying that position fixes aren't calculated by the receiver in SiRF mode.... just that it needs further processing to get lat/lon out of it.


Oh I know that you know what you were talking about. How Rumsfeld is that?

While the conversion of the binary stream to lat/long is not trivial (mostly tedious). I would be very impressed if anyone coded up the math to process GPS signals. Anyone who can do both the signal processing and the geodesy is scary smart.
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Postby lincomatic » Tue May 18, 2004 2:26 pm

Dutch wrote:Is that worth it to get positionupdates every half second meaning our max moved distance is now 6,9 meters at the 50 Km/h speed ?
BTW I haven't checked if the 1 hz update frequency limit is lifted when in Sirf binary mode, so don't even know if a faster update rate is available.

Just my 0.02€'s worth...

Dutch


using the SiRF configuration utilities, AFAIK, it's impossible to lower the update rate to <1Hz. and i agree, for the purposes of NS, a faster update rate is useless. i doubt that marius even samples it faster than that in the program to begin with.
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Postby lincomatic » Tue May 18, 2004 2:30 pm

sparafina wrote:Oh I know that you know what you were talking about. How Rumsfeld is that?

While the conversion of the binary stream to lat/long is not trivial (mostly tedious). I would be very impressed if anyone coded up the math to process GPS signals. Anyone who can do both the signal processing and the geodesy is scary smart.


help me get it out of my head...i've had it stuck in my head for 2 weeks now from all the incessant newscasts (sing to the tune of elmo's world): "lala lala, lala lala, Rummy's World, (Rummy's World), lala lala, lala lala, Rummy's World ..."

there are some really crappy trimble chipset-based units that use host-based processing. i had horrible performance w/ them on an ipaq. losing the fix every few seconds, stupid inertial fix algorithm (like SiRF x-track), besides having to waste memory for the driver and CPU bandwidth for the calculations... BAD DOG! BAD!
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Help me for sirf protocol!!!

Postby fabdominici » Wed Sep 15, 2004 6:44 am

Which is the system reference for satellites position of message id 30 (0x1E) in a SIRF protocoll?
I've this problem because I download satellites positions and pseudorange but I don't find my position after a system solution.
My software version is: 220.006.000ES-LD03
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