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Mancio

Hi,

I'm using  an Emtac BT GPS receiver to acquire gps signals but RTKNAVI does not support NMEA0183 format as Rover input stream. Please can you give me any suggestions to realize an input stream ( for a DGPS application ) without changing the receiver? 


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DavidKelley@ITSware.net

Francesco Mancino:
You do not need to send NMEA from it, you probably need to send RTCM to it.   You probably can not do classical RTK with it.

If you are planning to use a DGPS corrections (not RTK), then it is likely the GNSS chip itself will do the navigation filter for you (in other words it is not externally done with RTKLIB and RTKnavi).  If that is your chosen path, seek for a local RTCM2.x data stream (local meaning <50km or so) and figure out how to send that data directly to you GNSS. 

I am not familiar with the "Emtac BT GPS receiver"  but a quick web search tells me that is uses the older SiRF Star II LP  chip set and therefore it seems to use only WAAS/EGNOS corrections.  You need to research that point first and foremost to be sure that it can accept DGPS from other sources.   As far as I am aware you will not get code and carrier from it, so there is not means to do an RTK style navigation solution.  RTKLIB can do a DGPS navigation solution, if you can get raw code from it.

Regards  DC Kelley


On 9/18/2016 5:34 PM, Francesco Mancino wrote:

Hi,

I'm using  an Emtac BT GPS receiver to acquire gps signals but RTKNAVI does not support NMEA0183 format as Rover input stream. Please can you give me any suggestions to realize an input stream ( for a DGPS application ) without changing the receiver? 




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Re: information

Mancio

David,

thanks for your suggestions. My main problem is the lack of a specific HW ( receiver and antenna ), so I've decided to operate in a Post Processing mode. Here, I have another problem :  I've not RINEX files of local observations  taken by a rover. So I'm thinking to use RINEX observation data of a network station like rover static data and correct them with NRTK-VRS technique. Please,  give me a feedback about my idea.

Thanks in advance.

FM




Da: FOSS-GPS <[hidden email]> per conto di David Kelley <[hidden email]>
Inviato: mercoledì 21 settembre 2016 01.00
A: [hidden email]
Oggetto: Re: [FOSS-GPS] information
 

Francesco Mancino:
You do not need to send NMEA from it, you probably need to send RTCM to it.   You probably can not do classical RTK with it.

If you are planning to use a DGPS corrections (not RTK), then it is likely the GNSS chip itself will do the navigation filter for you (in other words it is not externally done with RTKLIB and RTKnavi).  If that is your chosen path, seek for a local RTCM2.x data stream (local meaning <50km or so) and figure out how to send that data directly to you GNSS. 

I am not familiar with the "Emtac BT GPS receiver"  but a quick web search tells me that is uses the older SiRF Star II LP  chip set and therefore it seems to use only WAAS/EGNOS corrections.  You need to research that point first and foremost to be sure that it can accept DGPS from other sources.   As far as I am aware you will not get code and carrier from it, so there is not means to do an RTK style navigation solution.  RTKLIB can do a DGPS navigation solution, if you can get raw code from it.

Regards  DC Kelley


On 9/18/2016 5:34 PM, Francesco Mancino wrote:

Hi,

I'm using  an Emtac BT GPS receiver to acquire gps signals but RTKNAVI does not support NMEA0183 format as Rover input stream. Please can you give me any suggestions to realize an input stream ( for a DGPS application ) without changing the receiver? 




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Re: information

DavidKelley@ITSware.net
Francesco Mancino:
Well as a practical matter, you really do not to want to record RINEX in the field, it is better (much smaller) to use the device's native binary format or an RTCM3 format and post process that to RINEX. 

> I've not RINEX files of local observations  taken by a rover
I am not sure I read this correctly but the above statement remains true. 

> So I'm thinking to use RINEX observation data of a network station like rover static data and correct them with NRTK-VRS technique.
Should work fine.  For this you need to gather either live caster data (use a free tool like SNIP and have it record whatever NTRIP data stream you need, see: use-snip.com) or use after the fact FTP data.

You may be able to use the FTP files provide by NGS and CORS.  The problem that many people have with those files is that after a week the data is decimated for long term storage, so your 1Hz data becomes 5/15 second data. So it is common to record the live data when you can get it off NTRIP and make your own records.   [Beside SNIP, the BNC tool is also adept at this]  Another issue is that NGS is only interested in high grade base stations about 70km apart, and many states in fact have sites with closer spacings.  As matter of current policy, NGS does not record those.  Its worth the time and trouble to learn about who has local stations you might want to get data from.  If you are limited to L1, you really need to find a station that is <15km from your rovers to do RTK things.

The other advantage of post processing is you can use better orbital and clock products which you can get from various places (and you can also get live from many NTRIP sources). 

On the whole your approach is quite sound IF  (the big if) your L1 only rover devices can in fact give code (pseudorange) AND carrier data.  If it can only give you code, you are more or less screwed.  [If that is the case, try to send it RTCM2.x data because is probably has some sort of  primitive Hatch filter to do some carrier smoothing and multipath rejection]

Good luck with this. 
Regards, David Kelley

PS: the carrier field in any RINEX file is the "L" (L1 or L2 etc.), if you do not see that field you do not have carrier data, here is a fragment from  a uBlox 6T (an L1 only device).  You can see the carrier for  SV "G20" was missing in this data set  (which was dropping out of view as the high negative Doppler rate and low SNR shows).
     4    C1    L1    D1    S1                              # / TYPES OF OBSERV
  2016     6     7    17    42   46.0000781     GPS         TIME OF FIRST OBS  
  2016     6     7    18     3   27.0000781     GPS         TIME OF LAST OBS   
                                                            END OF HEADER      
 16  6  7 17 42 46.0000781  0 12G 7G 8G26G20G21G15G16G27G18G10S20G 4
  24315075.481   127776517.3292        448.410          29.000 
  22629267.575   118917537.1101       2271.698          32.000 
  21895722.936   115062756.905       -3156.582          42.000 
  25179786.705                       -3549.886          20.000 
  23308387.593   122486312.002       -2759.055          46.000 
  25514482.824   134079506.961         333.453          33.000 
  20601440.208   108261249.8101      -1454.798          43.000 
  20620768.706   108362926.6981        797.603          40.000 
  22056801.307   115909274.4371       -833.425          46.000 
  21617601.357   113601266.278        1698.172          47.000 
  37871568.996   199016439.7911       -286.053          29.000 
  23186586.975   121846252.716       -3871.296          40.000 



On 10/10/2016 5:55 PM, Francesco Mancino wrote:

David,

thanks for your suggestions. My main problem is the lack of a specific HW ( receiver and antenna ), so I've decided to operate in a Post Processing mode. Here, I have another problem :  I've not RINEX files of local observations  taken by a rover. So I'm thinking to use RINEX observation data of a network station like rover static data and correct them with NRTK-VRS technique. Please,  give me a feedback about my idea.

Thanks in advance.

FM




Da: FOSS-GPS [hidden email] per conto di David Kelley [hidden email]
Inviato: mercoledì 21 settembre 2016 01.00
A: [hidden email]
Oggetto: Re: [FOSS-GPS] information
 

Francesco Mancino:
You do not need to send NMEA from it, you probably need to send RTCM to it.   You probably can not do classical RTK with it.

If you are planning to use a DGPS corrections (not RTK), then it is likely the GNSS chip itself will do the navigation filter for you (in other words it is not externally done with RTKLIB and RTKnavi).  If that is your chosen path, seek for a local RTCM2.x data stream (local meaning <50km or so) and figure out how to send that data directly to you GNSS. 

I am not familiar with the "Emtac BT GPS receiver"  but a quick web search tells me that is uses the older SiRF Star II LP  chip set and therefore it seems to use only WAAS/EGNOS corrections.  You need to research that point first and foremost to be sure that it can accept DGPS from other sources.   As far as I am aware you will not get code and carrier from it, so there is not means to do an RTK style navigation solution.  RTKLIB can do a DGPS navigation solution, if you can get raw code from it.

Regards  DC Kelley


On 9/18/2016 5:34 PM, Francesco Mancino wrote:

Hi,

I'm using  an Emtac BT GPS receiver to acquire gps signals but RTKNAVI does not support NMEA0183 format as Rover input stream. Please can you give me any suggestions to realize an input stream ( for a DGPS application ) without changing the receiver? 





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-- 
Regards,
David Kelley
ITS Programs Manager
SubCarrier Systems Corp. (SCSC)
1833 East Foothill Blvd. Glendora, CA USA  91741
626-485-7528 (Cell)      888-950-8747 (Main)
626-513-7715 (Office)    888-613-0757 (Fax)
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