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Cellular forums Home > Archive > GPS > February 2007 > gps18 5Hz: raw data or NMEA?
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gps18 5Hz: raw data or NMEA?
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| Giorgio 2007-02-07, 12:33 pm |
| Hi to all,
I've got a problem and I've thought to ask to the readers of this NG that
seems to be very expert :-)
I have to set up a system to track the route of a car. I am not interested
in precision of the absolute position, but in times and routes, so I have
bought 2 garmin gps18 hoping that using two of them I can get better results
without buying some very expensive receiver. My first intention was to keep
one of the two receivers still and the other on the car, save the nmea
sentences and then compare them to obtain a precision better than simple
averaging, but I am not sure that this method will bring me to good results.
According to some rough calculation I made, some bias errors (like the
ionospheric and tropospheric ones) should get smaller (even simply comparing
final coordinates of the nmea sentences), but I'm afraid that some other
error in the measurement can make the result worse. To obtain better results
I should extract the raw measurement data and compare them like dgps: from a
mathematical point of view this should take to better results, but,
considering the low precision level of my receiver, am I sure that the
results will be really better?
Besides I am not an expert programmer, so I should use software like gringo
or asynk... are they suitable for the gps18 5Hz.
Thanks in advance for your replies! Sorry for my bad English.
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| Marc Brett 2007-02-07, 3:33 pm |
| On Wed, 7 Feb 2007 18:15:25 +0100, "Giorgio" < giorgiocorini0@liber
o.it> wrote:
>Hi to all,
>I've got a problem and I've thought to ask to the readers of this NG that
>seems to be very expert :-)
You'll get what you pay for, I'm afraid ;-)
>I have to set up a system to track the route of a car. I am not interested
>in precision of the absolute position, but in times and routes, so I have
>bought 2 garmin gps18 hoping that using two of them I can get better results
>without buying some very expensive receiver.
If you can quantify your requirements, any advice will be a lot more relevant.
According to Garmin, you can get 3 m position accuracy 95% typical, if you use
WAAS. Are you in N. America where WAAS is available? If in Europe, EGNOS will
be operational Real Soon Now. Is this not good enough?
>My first intention was to keep
>one of the two receivers still and the other on the car, save the nmea
>sentences and then compare them to obtain a precision better than simple
>averaging, but I am not sure that this method will bring me to good results.
This is the "poor man's DGPS", and it's not worth bothering with. See, for
example http://gpsinformation.net/main/poordgps.htm
>According to some rough calculation I made, some bias errors (like the
>ionospheric and tropospheric ones) should get smaller (even simply comparing
>final coordinates of the nmea sentences), but I'm afraid that some other
>error in the measurement can make the result worse. To obtain better results
>I should extract the raw measurement data and compare them like dgps: from a
>mathematical point of view this should take to better results, but,
>considering the low precision level of my receiver, am I sure that the
>results will be really better?
>Besides I am not an expert programmer, so I should use software like gringo
>or asynk... are they suitable for the gps18 5Hz.
>Thanks in advance for your replies! Sorry for my bad English.
Non essere spiacente! Inglese siete migliori del mio italiano!
Both Async and Gringo (demo version) are free. Download them and see if they
work for the GPS 18 5Hz. It's been a long time since I read the docs for either
program, but I seem to remember that there are 3 possible receiver model
families to choose from -- try each one and see if it works...
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