[teqc] Converting Android GPS data to Rinex file format

Gerald Creager gerry.creager at tamu.edu
Wed Oct 13 13:44:10 MDT 2010


While there are some types of post-processing that can be achieved with 
latitude, longitude and elipsoid height, such as long-term averaging, 
these will not yield the same degree of success a least-squares 
approximation of position. In general, as indicated earlier, 
pseudorange, pseudorange-rate, precise timing information, precise 
ephemeris information and spacecraft health go into the more rigorous 
postprocessing methods.

It looks like the Android only provides latitude, longitude, height, 
speed over ground, and heading ($GPRMC) data from the VERY brief review 
I've done (others can correct me). $GPGST might be of some use (I've 
never seen it output by a consumer-grade receiver, though) but I believe 
it's just noise data and not real pseudorange data.

In other words, while you can experiment with some form of 
post-processing, it doesn't look promising.

gerry

Lalitha wrote:
> Thanks Jim for the clear reply. Finally one more question.
> Is there any other methods to achieve post processing dgps corrections 
> other than converting to Rinex format.
> I understand from all of your replies that the underlying raw gps data 
> is must for doing corrections with the base station gps data.
> But still, want to give a try asking if there is any other ways to do it.
> 
> Thanks,
> Lalitha.
> 
> On Wed, Oct 13, 2010 at 10:44 AM, James Johnson <jjohnson at ucar.edu 
> <mailto:jjohnson at ucar.edu>> wrote:
> 
>     Hi Lalitha,
> 
>     It is not possible to generate RINEX from an android phone.  This is
>     because the raw data required for RINEX is not exposed by the
>     Android API.  You can get some information about the SVs tracked and
>     a position, but you can not get the raw Pseudo range data.  The NMEA
>     strings are not useful for generating RINEX as well, simply because
>     the data is not there.
> 
>     Sorry for the sad news.
> 
>     Best Regards,
>     Jim Johnson
>     On Oct 13, 2010, at 11:40 AM, Lalitha wrote:
> 
>      > Hi Homan,
>      >
>      > Tons of thanks for the detailed reply. I've been searching the
>     net and posting in all the android, gps forums for the past 10 days
>     and didn't get any response till now. Thanks to teqc mailing list.
>      >
>      > Q1. I checked the android api for the gps data. It provides GPS
>     Satellite info from which we can get elevation, PRN (pseudo-random
>     number), snr, Almanac, ephemeris data etc.
>      >      Ref :
>     http://developer.android.com/reference/android/location/GpsStatus.html
>      > With these data, will it be possible to generate Rinex file
>     directly from android app?.
>      >
>      > Q2. Also, there is a nmealistener provided in the android api
>     using which we can capture gps nmea strings. Will this data be
>     useful by anyway to translate to rinex format? (Though, I coudnt
>     succeed capturing nmea string using my htc magic phone, I can try
>     with some other phones if this data will be  useful for post
>     processing).
>      >
>      > Thanks,
>      > Lalitha.
>      >
>      > On Wed, Oct 13, 2010 at 9:58 AM, Homan, Thomas
>     <thoman at co.gila.az.us <mailto:thoman at co.gila.az.us>> wrote:
>      > Lalitha,
>      >
>      >
>      > .gpx files cannot be converted to Rinex as they don’t contain the
>     necessary data elements. If I remember correctly, the api only
>     outputs the final latitude and longitude values. I don’t believe the
>     underlying raw gps data is accessible but I’m just getting started
>     on Exclipse.
>      >
>      >
>      > To generate a Rinex file you need to have access to underlying
>     information such as pseudorange, carrier phase and other data from
>     each satellite in the GPS constellation. As an example, below are a
>     .gpx file compared to a Rinex file that I collected in 2005. Each of
>     the 7 satellites visible has a set of 7 data elements logged out of
>     my $$$ survey grade receiver and this happens each logging period.
>      >
>      >
>      > Peruse the api docs and see if there is access to the underlying
>     data and not the final coordinates. If not, then you might be out of
>     luck. One thing you might explore is if the android OS supports
>     inserting DGPS correctors so you could get real time sub-meter
>     accuracies.
>      >
>      >
>      > Hope this helps some.
>      >
>      >
>      > Tom
>      >
>      >
>      > GPX
>      >
>      > <?xml version="1.0" encoding="ISO-8859-1"?>
>      >
>      > <gpx xmlns="http://www.topografix.com/GPX/1/1"
>     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.1"
>     creator="Doug Forster's map viewer"
>     xsi:schemaLocation="http://www.topografix.com/GPX/1/1
>     http://www.topografix.com/GPX/1/1/gpx.xsd">
>      >
>      > <wpt lat="-42.48781" lon="172.29404">
>      >
>      > <ele>1273</ele>
>      >
>      > <name>NwDvls</name>
>      >
>      > <cmt> 30/01/10 19:14</cmt>
>      >
>      > <desc>New Devils Den Biv</desc>
>      >
>      > <sym>Anchor</sym>
>      >
>      > <extensions>
>      >
>      > <type xmlns="Freshmap">Place</type>
>      >
>      > <TrackColor xmlns="Freshmap">0</TrackColor>
>      >
>      > <FontSize xmlns="Freshmap">90</FontSize>
>      >
>      > <GPSColor xmlns="Freshmap">14</GPSColor>
>      >
>      > <Layout xmlns="Freshmap">5</Layout>
>      >
>      > </extensions>
>      >
>      > </wpt>
>      >
>      > </gpx>
>      >
>      >
>      > Rinex
>      >
>      > 05 10 12 14 44 45.0000000  0  7G 1G24G23G20G16G25G11
>      >
>      >   18540407.76711  14441990.35651  22140106.912    22140108.9425  
>     22140103.6715
>      >
>      >      -1502.342       -1170.656
>      >
>      >   18405511.80411  14342294.04151  23619878.513    23619880.7005  
>     23619875.3565
>      >
>      >        382.895         298.360
>      >
>      >   18279304.44211  14260112.94351  22317896.240    22317897.3485  
>     22317888.9405
>      >
>      >       2122.449        1653.856
>      >
>      >   18331079.75811  14289623.90551  20672596.529    20672597.6675  
>     20672590.3895
>      >
>      >       1386.704        1080.549
>      >
>      >   18282886.39611  14256935.72751  21779940.978    21779941.1535  
>     21779934.4995
>      >
>      >       2177.108        1696.448
>      >
>      >   18595837.79911  14470056.42251  21824971.770    21824972.4395  
>     21824966.6485
>      >
>      >      -2263.324       -1763.629
>      >
>      >   18612482.40511  14492926.57751  23828871.571    23828874.4325  
>     23828869.0685
>      >
>      >      -2470.753       -1925.262
>      >
>      >
>      > From: teqc-bounces at ls.unavco.org
>     <mailto:teqc-bounces at ls.unavco.org>
>     [mailto:teqc-bounces at ls.unavco.org
>     <mailto:teqc-bounces at ls.unavco.org>] On Behalf Of Lalitha
>      > Sent: Wednesday, October 13, 2010 9:03 AM
>      > To: teqc at ls.unavco.org <mailto:teqc at ls.unavco.org>;
>     gpstech at ls.unavco.org <mailto:gpstech at ls.unavco.org>
>      > Subject: [teqc] Converting Android GPS data to Rinex file format
>      >
>      >
>      > Hi,
>      >
>      > How do i convert the gps data I get from Android GPS Receiver
>     into Rinex file format in order to do Post processing corrections.
>      > I can write the gps data into .gpx format using the android api
>     provided. I use HTC Magic phone with 2.2 api version.
>      > I cudnt find option for android in the teqc toolkit. Can anyone
>     help how do I convert to Rinex?
>      > Also I'm looking for the post processing softwares or service
>     available for evaluation. I could find only one free evaluation
>     software 'PPro2' from Kinematic GPS.
>      > Is there any other free post processing software present?
>      >
>      > Thanks,
>      > Lalitha.
>      >
>      >
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>      >
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-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843


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