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Whats the difference SiRF, SiRF II, NMEA?

 
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mshah
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PostPosted: Sun Sep 14, 2003 8:04 am    Post subject: Whats the difference SiRF, SiRF II, NMEA? Reply with quote

I've been wanting to get a PocketPC GPS system for a while and I think I will settle for the TT Navigator 2 (but will wait for a few more people's opinion first).



I am also deciding about whether to go for the TT Nav 2 included GPS receiver or go for another GPS receiver like the bluetooth one (I've read the previous thread about the difference between the two), but what I am after is an explanation between the different protocols.



Reading the news article "New Tomtom GPS Receiver" which was posted on 12 March 2003. It Names all these protocols:

  • NMEA-0183 v2.0
  • SiRF Binary protocol
  • SiRF II chipsets
  • GGA
  • GSA
  • GSV
  • RMC
  • VTG
  • GLL
  • SiRF Binary plus proprietary messages
  • and I'm guessing if there's a NMEA-183 v2.0 there's probably a v1.0 too?




So my questions are:

  1. What are the difference between these?
  2. Which one's of them is the best?
  3. Which one is the most supported?
  4. By choosing one of them, does that restrict the options for future upgrade in GPS software?
  5. What is the accuracy and speed of aquisition between them all?




Thanks for your help.
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Dave
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PostPosted: Sun Sep 14, 2003 8:04 am    Post subject: Whats the difference SiRF, SiRF II, NMEA? Reply with quote

Milan, the only protocols that are available are NMEA0183, SiRF, SiRFI, SiRFII, SiRFIIe, SiRFIIe/LP and SiRFIIt. All GPS Receivers support NMEA and a flavour of SiRF. Most support SiRFI where the newer ones will support SiRFII/SiRFIIe.



GGA, GSA, GSV, RMC, VTG, GLL are part of the NMEA standard. They allow different options within NMEA to customise the data coming back and to tweak it.



  1. 99% of GPS Software programs support NMEA, some do support SiRF, but beware some programs like TomTom Navigator do not like working in SiRF west of meridian due to bugs in the software
  2. As per 1, NMEA is the industry standard that is primarily used. Some people prefer SiRF, it has a faster re-acquisition time, but we're talking milliseconds, which really isn't comparable when using a GPS system in car.
  3. NMEA
  4. No, think of 56k modems, you had X2 and K56flex, both were good, but eventually the industry had, had enough and decided one shold prevail, X2 prevailed and was named V.90. One may eventually become the standard here, but if it doesn't, all GPS Receivers created for well over the past year support both NMEA and SiRF formats
  5. Pretty much identical unless you're going to time milliseconds on a stop watch, then you have human error for starting and stopping the button. Acquisition time is down to the receiver, the electronics within it and how they can interfere with each other. Rule of thumb is most receivers will acquire a signal in less than a minute, most around 50 secs on a cold start (8+ hours powered off), if you're luckily and have a clear view of the sky the quickest time a cold start will give you is 30 seconds. A warm or hot start you should see around 20 and 5 seconds respectively.
Don't read into the hardware too much. Check out our TTFF Comparison table if you're still a little worried, and also our GPS Hardware Page which will show you which hardware will work with which PDA.



The slowest receivers I've come across of all are the Navman 3000/3400 sleeve and the Pretec LP. You'll see this reflected in our TTFF Comparison table.
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mshah
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PostPosted: Sun Sep 14, 2003 8:04 am    Post subject: Whats the difference SiRF, SiRF II, NMEA? Reply with quote

Thanks for the help Dave.



So what's the general compatibility between The Emtac bluetooth GPS receiver and TomTom 2. From what I can find they both support NMEA and SiRF II. Which one would I use when setting them up? Thanks again.
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Dave
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PostPosted: Sun Sep 14, 2003 8:04 am    Post subject: Whats the difference SiRF, SiRF II, NMEA? Reply with quote

Ask me in a few days as I'm getting my hands on one for a week. Mike uses the Emtac/Socket BT with TomTom Navigator 1 and it works flawlessly, so I don't forsee any problems.



With TomTom Navigator 2 you would want to use NMEA. All of the GPS Receivers pretty much come configured for NMEA out of the box.
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mshah
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PostPosted: Sun Sep 14, 2003 8:04 am    Post subject: Whats the difference SiRF, SiRF II, NMEA? Reply with quote

I take it the accuracy between NMEA and SiRF II is the same then?
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Dave
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PostPosted: Sun Sep 14, 2003 8:04 am    Post subject: Whats the difference SiRF, SiRF II, NMEA? Reply with quote

It's pretty much identical. They're using the same satellites, the only way you'll get better accuracy is by using DGPS/WAAS/EGNOS by utilising ground stations for better accuracy.
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mshah
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PostPosted: Sun Sep 14, 2003 8:04 am    Post subject: Whats the difference SiRF, SiRF II, NMEA? Reply with quote

Ok now I'm confused. What is DGPS/WAAS/EGNOS? Is it something I should have to look into with my solution comprising of Emtac GPS with TT Nav 2 and Ipaq 3870? Are these more accurate solutions more for businesses or are they used for in-car navigation?
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Dave
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PostPosted: Sun Sep 14, 2003 8:04 am    Post subject: Whats the difference SiRF, SiRF II, NMEA? Reply with quote

Sorry, DGPS/WAAS/EGNOS is a way of bringing a greater accuracy to GPS within just a few feet, but it requires being able to have generally what is called a WAAS enabled receiver. WAAS is Wide Area Augmentation System. This is used by the US and the satellites we use, Europe are bringing online EGNOS which is effectively the same thing.



It's something to look into if you want pin-point accuracy and you're not in a city amongst large buildings or driving in a car. What happens is you not only receive signals from satellites in the sky, but also from ground stations which can then triangulate you on the ground giving a much better accuracy with GPS.
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fysmd
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PostPosted: Sun Sep 14, 2003 8:04 am    Post subject: Whats the difference SiRF, SiRF II, NMEA? Reply with quote

Are there any of these ground stations in the UK? My Garmin gizmo supports WAAS.



Ian
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