Signal to noise ratio

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Signal to noise ratio

Robert Luben
I am using GPSBabel (Version 1.5.2 under Linux) to extract data from
QStarz BT_Q1000XT GPS as part of a research study. The GPS comes with its
own Windows based interactive software but since we have lots GPSs to
download and initialize, using GPSBabel in a shell script is the most
efficient and quickest method. The current method is a two stage process -
first downloading to .gpx format and later converting to .csv using
iblue_757.style XCSV Style
(https://code.google.com/p/gpsbabel/source/browse/trunk/gpsbabel/style/iblue757.style).
This works fine except that the variable SNR (signal to noise ratio) is
missing. I guess SNR isn't a very commonly used variable but it we use it
to give an indication of whether the GPS is being worn inside a building.
SNR should appear in the SAT INFO section with multiple SNRs for each
record.  However in iblue_757.style the SAT INFO section has "IFIELD
IGNORE".  SNR is definitely recorded by the machine since the proprietary
software is able to extract it to .csv.

Does anyone know how it might be possible to capture SNR using gpsbabel or
suggest some other way we can capture SNR within a script?

Robert


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Re: Signal to noise ratio

Robert Lipe-4
You're right. SNR is uncommon.  If you're pitstopping the data through GPX, you'll certainly lose it.   When you're indoors, under a bridge, etc. you should see spikes in HDOP and VDOP (horizontal/vertical dilution of precision) and that's more likely to be preserved across formats.  We don't really have a place for a "raw" SNR value in the data structure that's shared between all the readers and writers, so we really can't do much with SNR.

However, there may be an easier way to get it.  This is completely weird in GPSBabel-land and I'd noticed it during code review, i'd probably have removed it.  There is a 'csv' option in the mtk reader that bizarrely writes a csv file that is apparently what the provided app uses.

http://www.gpsbabel.org/htmldoc-development/fmt_mtk.html#fmt_mtk_o_csv for use.

There is code that looks like it's writing SNR.  See
https://code.google.com/p/gpsbabel/source/browse/trunk/gpsbabel/mtk_logger.cc?r=4941#923  The writer is even unit tested somewhat so it's not totally broken, but the test data that we have doesn't have SNR data as one of the columns.

This is such a weird wart in GPSBabel that I can't say if it works or anybody but the original author has ever tried it, but if it plays out, that's probably a winning lottery ticket for you.

RJL

On Fri, Apr 10, 2015 at 7:28 AM, Robert Luben <[hidden email]> wrote:
I am using GPSBabel (Version 1.5.2 under Linux) to extract data from
QStarz BT_Q1000XT GPS as part of a research study. The GPS comes with its
own Windows based interactive software but since we have lots GPSs to
download and initialize, using GPSBabel in a shell script is the most
efficient and quickest method. The current method is a two stage process -
first downloading to .gpx format and later converting to .csv using
iblue_757.style XCSV Style
(https://code.google.com/p/gpsbabel/source/browse/trunk/gpsbabel/style/iblue757.style).
This works fine except that the variable SNR (signal to noise ratio) is
missing. I guess SNR isn't a very commonly used variable but it we use it
to give an indication of whether the GPS is being worn inside a building.
SNR should appear in the SAT INFO section with multiple SNRs for each
record.  However in iblue_757.style the SAT INFO section has "IFIELD
IGNORE".  SNR is definitely recorded by the machine since the proprietary
software is able to extract it to .csv.

Does anyone know how it might be possible to capture SNR using gpsbabel or
suggest some other way we can capture SNR within a script?

Robert


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Re: Signal to noise ratio

Robert Luben
Hi Robert,

Thank you for your very helpful response and explanation.  This seemed
like the perfect solution but unfortunately there is a problem. I compared
the output from GPSBabel with the output from the proprietary software
that comes with our GPS.  The output was identical for all fields except
Signal to Noise Ratio.  Typical values of SNR from the proprietary
software had a nice bell shape distribution with a mean of 27 and an SD of
8. However this was very different to the GPSBabel SNR where 11 was the
most common value and 90% of values were between 7 and 15 but the data had
a huge tail with random values up to 32,000.

To check my method I also compared the SID values (the first number in the
the SID-ELE-AZI-SNR blocks) between outputs.  For SID, GPSBabel matched
the proprietary software exactly so I am confident that my method is
working properly.  Do you have any explanation for the differences in SNR?
I'm happy to send you my data and programs if it helps.


On Fri, 10 Apr 2015, Robert Lipe wrote:

> You're right. SNR is uncommon.  If you're pitstopping the data through GPX, you'll certainly lose it.   When you're indoors, under a
> bridge, etc. you should see spikes in HDOP and VDOP (horizontal/vertical dilution of precision) and that's more likely to be preserved
> across formats.  We don't really have a place for a "raw" SNR value in the data structure that's shared between all the readers and
> writers, so we really can't do much with SNR.
>
> However, there may be an easier way to get it.  This is completely weird in GPSBabel-land and I'd noticed it during code review, i'd
> probably have removed it.  There is a 'csv' option in the mtk reader that bizarrely writes a csv file that is apparently what the
> provided app uses.
>
> http://www.gpsbabel.org/htmldoc-development/fmt_mtk.html#fmt_mtk_o_csv for use.
>
> There is code that looks like it's writing SNR.  See
> https://code.google.com/p/gpsbabel/source/browse/trunk/gpsbabel/mtk_logger.cc?r=4941#923  The writer is even unit tested somewhat so
> it's not totally broken, but the test data that we have doesn't have SNR data as one of the columns.
>
> This is such a weird wart in GPSBabel that I can't say if it works or anybody but the original author has ever tried it, but if it
> plays out, that's probably a winning lottery ticket for you.
>
> RJL
>
> On Fri, Apr 10, 2015 at 7:28 AM, Robert Luben wrote:
>       I am using GPSBabel (Version 1.5.2 under Linux) to extract data from
>       QStarz BT_Q1000XT GPS as part of a research study. The GPS comes with its
>       own Windows based interactive software but since we have lots GPSs to
>       download and initialize, using GPSBabel in a shell script is the most
>       efficient and quickest method. The current method is a two stage process -
>       first downloading to .gpx format and later converting to .csv using
>       iblue_757.style XCSV Style
>       (https://code.google.com/p/gpsbabel/source/browse/trunk/gpsbabel/style/iblue757.style).
>       This works fine except that the variable SNR (signal to noise ratio) is
>       missing. I guess SNR isn't a very commonly used variable but it we use it
>       to give an indication of whether the GPS is being worn inside a building.
>       SNR should appear in the SAT INFO section with multiple SNRs for each
>       record.  However in iblue_757.style the SAT INFO section has "IFIELD
>       IGNORE".  SNR is definitely recorded by the machine since the proprietary
>       software is able to extract it to .csv.
>
>       Does anyone know how it might be possible to capture SNR using gpsbabel or
>       suggest some other way we can capture SNR within a script?
>
>       Robert

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Re: Signal to noise ratio

Robert Lipe-4
It's possible that the provided software is doing some clever post-processing of the data.  As shown in the link I gave you to the code, we don't do anything other than read the bytes and put them in the output.

If you have additional documention on what those fields mean from the unit or have additional processing on what we could do with those fields to be more helpful, I'd welcome a patch.

RJL

On Tue, Jun 30, 2015 at 12:02 PM, Robert Luben <[hidden email]> wrote:
Hi Robert,

Thank you for your very helpful response and explanation.  This seemed
like the perfect solution but unfortunately there is a problem. I compared
the output from GPSBabel with the output from the proprietary software
that comes with our GPS.  The output was identical for all fields except
Signal to Noise Ratio.  Typical values of SNR from the proprietary
software had a nice bell shape distribution with a mean of 27 and an SD of
8. However this was very different to the GPSBabel SNR where 11 was the
most common value and 90% of values were between 7 and 15 but the data had
a huge tail with random values up to 32,000.

To check my method I also compared the SID values (the first number in the
the SID-ELE-AZI-SNR blocks) between outputs.  For SID, GPSBabel matched
the proprietary software exactly so I am confident that my method is
working properly.  Do you have any explanation for the differences in SNR?
I'm happy to send you my data and programs if it helps.


On Fri, 10 Apr 2015, Robert Lipe wrote:

You're right. SNR is uncommon.  If you're pitstopping the data through GPX, you'll certainly lose it.   When you're indoors, under a
bridge, etc. you should see spikes in HDOP and VDOP (horizontal/vertical dilution of precision) and that's more likely to be preserved
across formats.  We don't really have a place for a "raw" SNR value in the data structure that's shared between all the readers and
writers, so we really can't do much with SNR.

However, there may be an easier way to get it.  This is completely weird in GPSBabel-land and I'd noticed it during code review, i'd
probably have removed it.  There is a 'csv' option in the mtk reader that bizarrely writes a csv file that is apparently what the
provided app uses.

http://www.gpsbabel.org/htmldoc-development/fmt_mtk.html#fmt_mtk_o_csv for use.

There is code that looks like it's writing SNR.  See
https://code.google.com/p/gpsbabel/source/browse/trunk/gpsbabel/mtk_logger.cc?r=4941#923  The writer is even unit tested somewhat so
it's not totally broken, but the test data that we have doesn't have SNR data as one of the columns.

This is such a weird wart in GPSBabel that I can't say if it works or anybody but the original author has ever tried it, but if it
plays out, that's probably a winning lottery ticket for you.

RJL

On Fri, Apr 10, 2015 at 7:28 AM, Robert Luben wrote:
      I am using GPSBabel (Version 1.5.2 under Linux) to extract data from
      QStarz BT_Q1000XT GPS as part of a research study. The GPS comes with its
      own Windows based interactive software but since we have lots GPSs to
      download and initialize, using GPSBabel in a shell script is the most
      efficient and quickest method. The current method is a two stage process -
      first downloading to .gpx format and later converting to .csv using
      iblue_757.style XCSV Style
      (https://code.google.com/p/gpsbabel/source/browse/trunk/gpsbabel/style/iblue757.style).
      This works fine except that the variable SNR (signal to noise ratio) is
      missing. I guess SNR isn't a very commonly used variable but it we use it
      to give an indication of whether the GPS is being worn inside a building.
      SNR should appear in the SAT INFO section with multiple SNRs for each
      record.  However in iblue_757.style the SAT INFO section has "IFIELD
      IGNORE".  SNR is definitely recorded by the machine since the proprietary
      software is able to extract it to .csv.

      Does anyone know how it might be possible to capture SNR using gpsbabel or
      suggest some other way we can capture SNR within a script?

      Robert


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Re: Signal to noise ratio

tsteven4-2
Robert Luben,

What formats can you download from the device?  nmea?  mkt binary? gpx?  nmea is well documented and easy to read, although we currently don't support the GPGSV sentence.
Can you supply a short sample of each and the SNR you get from the proprietary software?

Thanks,
Steve

On 6/30/2015 11:18 AM, Robert Lipe wrote:
It's possible that the provided software is doing some clever post-processing of the data.  As shown in the link I gave you to the code, we don't do anything other than read the bytes and put them in the output.

If you have additional documention on what those fields mean from the unit or have additional processing on what we could do with those fields to be more helpful, I'd welcome a patch.

RJL

On Tue, Jun 30, 2015 at 12:02 PM, Robert Luben <[hidden email]> wrote:
Hi Robert,

Thank you for your very helpful response and explanation.  This seemed
like the perfect solution but unfortunately there is a problem. I compared
the output from GPSBabel with the output from the proprietary software
that comes with our GPS.  The output was identical for all fields except
Signal to Noise Ratio.  Typical values of SNR from the proprietary
software had a nice bell shape distribution with a mean of 27 and an SD of
8. However this was very different to the GPSBabel SNR where 11 was the
most common value and 90% of values were between 7 and 15 but the data had
a huge tail with random values up to 32,000.

To check my method I also compared the SID values (the first number in the
the SID-ELE-AZI-SNR blocks) between outputs.  For SID, GPSBabel matched
the proprietary software exactly so I am confident that my method is
working properly.  Do you have any explanation for the differences in SNR?
I'm happy to send you my data and programs if it helps.


On Fri, 10 Apr 2015, Robert Lipe wrote:

You're right. SNR is uncommon.  If you're pitstopping the data through GPX, you'll certainly lose it.   When you're indoors, under a
bridge, etc. you should see spikes in HDOP and VDOP (horizontal/vertical dilution of precision) and that's more likely to be preserved
across formats.  We don't really have a place for a "raw" SNR value in the data structure that's shared between all the readers and
writers, so we really can't do much with SNR.

However, there may be an easier way to get it.  This is completely weird in GPSBabel-land and I'd noticed it during code review, i'd
probably have removed it.  There is a 'csv' option in the mtk reader that bizarrely writes a csv file that is apparently what the
provided app uses.

http://www.gpsbabel.org/htmldoc-development/fmt_mtk.html#fmt_mtk_o_csv for use.

There is code that looks like it's writing SNR.  See
https://code.google.com/p/gpsbabel/source/browse/trunk/gpsbabel/mtk_logger.cc?r=4941#923  The writer is even unit tested somewhat so
it's not totally broken, but the test data that we have doesn't have SNR data as one of the columns.

This is such a weird wart in GPSBabel that I can't say if it works or anybody but the original author has ever tried it, but if it
plays out, that's probably a winning lottery ticket for you.

RJL

On Fri, Apr 10, 2015 at 7:28 AM, Robert Luben wrote:
      I am using GPSBabel (Version 1.5.2 under Linux) to extract data from
      QStarz BT_Q1000XT GPS as part of a research study. The GPS comes with its
      own Windows based interactive software but since we have lots GPSs to
      download and initialize, using GPSBabel in a shell script is the most
      efficient and quickest method. The current method is a two stage process -
      first downloading to .gpx format and later converting to .csv using
      iblue_757.style XCSV Style
      (https://code.google.com/p/gpsbabel/source/browse/trunk/gpsbabel/style/iblue757.style).
      This works fine except that the variable SNR (signal to noise ratio) is
      missing. I guess SNR isn't a very commonly used variable but it we use it
      to give an indication of whether the GPS is being worn inside a building.
      SNR should appear in the SAT INFO section with multiple SNRs for each
      record.  However in iblue_757.style the SAT INFO section has "IFIELD
      IGNORE".  SNR is definitely recorded by the machine since the proprietary
      software is able to extract it to .csv.

      Does anyone know how it might be possible to capture SNR using gpsbabel or
      suggest some other way we can capture SNR within a script?

      Robert



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Re: Signal to noise ratio

Robert Luben
In reply to this post by Robert Lipe-4

It may be post-processing, but the GPSBabel csv output looks a little odd
with some SID-ELE-AZI-SNR blocks starting with a hash and some not and
large numbers appearing in the last block. Occasionally the last block
will have a double dash (eg 13--25024).  I have pasted below equivalent
lines from the two csv outputs which are pretty typical to show you what I
mean. (Proprietary SNR: 00,37,29,24 etc, GPSBabel SNR: 11,11, ...,31028)

Proprietary:
1, T, 2015/01/01, 12:01:01, 2015/01/01, 12:01:01, 0, DGPS, 52.00000000, N,
1.20000000, E, 79.034 M, 2.504 km/h, 0.000000, 0, 0.000, 1.50, 1.20, 0.91,
7/11,
21-00-00-00;05-00-00-37;07-00-00-29;13-00-00-24;19-00-00-24;28-00-00-22;15-00-00-35;27-00-00-00;30-00-00-27;20-00-00-00;10-00-00-00,
0.29 M

GPSBabel:
1,T,2015/01/01,12:01:01.000,DGPS,52.000000,N,1.200000,E,79.034 m,2.504
km/h,1.50,1.20,0.91,7(11),21-11;#05-11;#07-11;#13-11;#19-11;#28-11;#15-11;27-11;#30-11;20-11;10-31028,
0.29 m,

I have compiled a few times with a modified mtk_logger.cc to understand
the code a bit better - I'll post a patch if I get anywhere.

tsteven4, I have tried several output formats (including GPX and nmea),
but SNR is not shown. I am using the csv option of mtk, which is the
closest to what I need, like this:

gpsbabel -t -w -i mtk,csv=test.csv -f /dev/ttyACM0 -o gpx -F test.gpx



On Tue, 30 Jun 2015, Robert Lipe wrote:

> It's possible that the provided software is doing some clever post-processing of the data.  As shown in the link I gave you to the
> code, we don't do anything other than read the bytes and put them in the output.
>
> If you have additional documention on what those fields mean from the unit or have additional processing on what we could do with those
> fields to be more helpful, I'd welcome a patch.
>
> RJL
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Re: Signal to noise ratio

tsteven4-2
Robert,

The hash indicates the satellite is used.  Perhaps it would be enlightening to add -D 6 to your command line.  If you could sent that output, and the gpsbabel created csv file, and the proprietary csv file maybe we can figure something out.  Is gpsbabel creating a data.bin file in the current directory?  If so it may be useful to have that as well.  None of the sample bin files we have in our regression have SID-ELE-AZI-SNR data, so it wouldn't be surprising if something doesn't work.

Steve

On 7/3/2015 11:06 AM, Robert Luben wrote:

It may be post-processing, but the GPSBabel csv output looks a little odd
with some SID-ELE-AZI-SNR blocks starting with a hash and some not and
large numbers appearing in the last block. Occasionally the last block
will have a double dash (eg 13--25024).  I have pasted below equivalent
lines from the two csv outputs which are pretty typical to show you what I
mean. (Proprietary SNR: 00,37,29,24 etc, GPSBabel SNR: 11,11, ...,31028)

Proprietary:
1, T, 2015/01/01, 12:01:01, 2015/01/01, 12:01:01, 0, DGPS, 52.00000000, N,
1.20000000, E, 79.034 M, 2.504 km/h, 0.000000, 0, 0.000, 1.50, 1.20, 0.91,
7/11,
21-00-00-00;05-00-00-37;07-00-00-29;13-00-00-24;19-00-00-24;28-00-00-22;15-00-00-35;27-00-00-00;30-00-00-27;20-00-00-00;10-00-00-00,
0.29 M

GPSBabel:
1,T,2015/01/01,12:01:01.000,DGPS,52.000000,N,1.200000,E,79.034 m,2.504
km/h,1.50,1.20,0.91,7(11),21-11;#05-11;#07-11;#13-11;#19-11;#28-11;#15-11;27-11;#30-11;20-11;10-31028,
0.29 m,

I have compiled a few times with a modified mtk_logger.cc to understand
the code a bit better - I'll post a patch if I get anywhere.

tsteven4, I have tried several output formats (including GPX and nmea),
but SNR is not shown. I am using the csv option of mtk, which is the
closest to what I need, like this:

gpsbabel -t -w -i mtk,csv=test.csv -f /dev/ttyACM0 -o gpx -F test.gpx



On Tue, 30 Jun 2015, Robert Lipe wrote:

It's possible that the provided software is doing some clever post-processing of the data.  As shown in the link I gave you to the
code, we don't do anything other than read the bytes and put them in the output.

If you have additional documention on what those fields mean from the unit or have additional processing on what we could do with those
fields to be more helpful, I'd welcome a patch.

RJL


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Re: Signal to noise ratio

tsteven4-2
Robert,

Please try this patch.  I think your trouble, at least with the little bit of the csv your shared below, is because you are not logging azimuth and elevation, but you are logging snr.  In this case we correctly figure out the sid size, but we don't pull the snr data from the proper location.  We really need a small sample with these options to add to our regression.  When you download data from your device a data.bin file should be created.  However, it is created in the QDir::tempPath() directory.  I think you will get a message "Download * -> *" that will tell you the full path to the data.bin file if you use command line option "-D 1" or higher.

The tempPath shoud be here:
On Unix/Linux systems this is the path in the TMPDIR environment variable or /tmp if TMPDIR is not defined. On Windows this is usually the path in the TEMP or TMP environment variable. Whether a directory separator is added to the end or not, depends on the operating system.

Steve

On 7/3/2015 5:07 PM, tsteven4 wrote:
Robert,

The hash indicates the satellite is used.  Perhaps it would be enlightening to add -D 6 to your command line.  If you could sent that output, and the gpsbabel created csv file, and the proprietary csv file maybe we can figure something out.  Is gpsbabel creating a data.bin file in the current directory?  If so it may be useful to have that as well.  None of the sample bin files we have in our regression have SID-ELE-AZI-SNR data, so it wouldn't be surprising if something doesn't work.

Steve

On 7/3/2015 11:06 AM, Robert Luben wrote:

It may be post-processing, but the GPSBabel csv output looks a little odd
with some SID-ELE-AZI-SNR blocks starting with a hash and some not and
large numbers appearing in the last block. Occasionally the last block
will have a double dash (eg 13--25024).  I have pasted below equivalent
lines from the two csv outputs which are pretty typical to show you what I
mean. (Proprietary SNR: 00,37,29,24 etc, GPSBabel SNR: 11,11, ...,31028)

Proprietary:
1, T, 2015/01/01, 12:01:01, 2015/01/01, 12:01:01, 0, DGPS, 52.00000000, N,
1.20000000, E, 79.034 M, 2.504 km/h, 0.000000, 0, 0.000, 1.50, 1.20, 0.91,
7/11,
21-00-00-00;05-00-00-37;07-00-00-29;13-00-00-24;19-00-00-24;28-00-00-22;15-00-00-35;27-00-00-00;30-00-00-27;20-00-00-00;10-00-00-00,
0.29 M

GPSBabel:
1,T,2015/01/01,12:01:01.000,DGPS,52.000000,N,1.200000,E,79.034 m,2.504
km/h,1.50,1.20,0.91,7(11),21-11;#05-11;#07-11;#13-11;#19-11;#28-11;#15-11;27-11;#30-11;20-11;10-31028,
0.29 m,

I have compiled a few times with a modified mtk_logger.cc to understand
the code a bit better - I'll post a patch if I get anywhere.

tsteven4, I have tried several output formats (including GPX and nmea),
but SNR is not shown. I am using the csv option of mtk, which is the
closest to what I need, like this:

gpsbabel -t -w -i mtk,csv=test.csv -f /dev/ttyACM0 -o gpx -F test.gpx



On Tue, 30 Jun 2015, Robert Lipe wrote:

It's possible that the provided software is doing some clever post-processing of the data.  As shown in the link I gave you to the
code, we don't do anything other than read the bytes and put them in the output.

If you have additional documention on what those fields mean from the unit or have additional processing on what we could do with those
fields to be more helpful, I'd welcome a patch.

RJL


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