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  1. #1
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    Jul 2009
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    GPS data using positioning module in Python s60

    Hi,

    I am interested in using the positioning module with the internal GPS sensor of N95 8GB. I found the very helpful code example here: http://wiki.forum.nokia.com/index.ph..._read_GPS_data
    However I have some question in relation to the use of GPS data from the positioning module.

    1 - What's the unit of GPS speed obtained from the positioning module. I suppose it is meters/sec but I am not sure.

    2 - What are the units of the GPS Longitude and Lattitude obtained in this code? I suppose they are in degrees but confimation would be very very helpful.

    3 - What is the highest update rate we can obtain from the GPS unit? In the example code 0.2 sec is used to print the GPS data. Does the measurement actually come at 5 Hz?

    4 - At the end of the example code, e32.ao_sleep(1) is used after every loop. Can we actaully use smaller sleep time at this step? Would choosing a shorter sleep time (let's say 0.01 sec) cause any problems for obtaining the GPS data?

    I would be very glad if anyone can help me with these questions.

    Selim

  2. #2
    Regular Contributor
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    Eindhoven, the Netherlands
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    Re: GPS data using positioning module in Python s60

    Hi,

    Quote Originally Posted by selimsolmaz View Post
    1 - What's the unit of GPS speed obtained from the positioning module. I suppose it is meters/sec but I am not sure.
    I think it is either km/h or m/s, I'm not really sure which.

    Quote Originally Posted by selimsolmaz View Post
    2 - What are the units of the GPS Longitude and Lattitude obtained in this code? I suppose they are in degrees but confimation would be very very helpful.
    They are indeed in degrees format using WGS84 datum. Positive numbers designate the northeast hemisphere (east of Greenwich, North of equator).

    Quote Originally Posted by selimsolmaz View Post
    3 - What is the highest update rate we can obtain from the GPS unit? In the example code 0.2 sec is used to print the GPS data. Does the measurement actually come at 5 Hz?
    The spec allows you to set updates in microseconds. I have tested this practically up to 0.2 seconds, which seems to work, but leave little processing power to the rest of the system. Also I'm not sure if I really got up to 5Hz updates. Now I generally use 0.5, which works fine for me.

    Quote Originally Posted by selimsolmaz View Post
    4 - At the end of the example code, e32.ao_sleep(1) is used after every loop. Can we actaully use smaller sleep time at this step? Would choosing a shorter sleep time (let's say 0.01 sec) cause any problems for obtaining the GPS data?
    Setting to 0.2 would work fine, setting to 0.01 may hog your cpu, your mileage may vary. I generally use 0.5, which means that I can still decently show a clock wich updates at least once per second.
    Why would you want to use such a short sleep time?

    Regards,
    Mark.
    Last edited by hurenkam; 2009-07-07 at 15:57.

  3. #3
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    Re: GPS data using positioning module in Python s60

    Quote Originally Posted by hurenkam View Post
    Hi,


    I think it is either km/h or m/s, I'm not really sure which.


    They are indeed in degrees format using WGS84 datum. Positive numbers designate the northeast hemisphere (east of Greenwich, North of equator).


    The spec allows you to set updates in microseconds. I have tested this practically up to 0.2 seconds, which seems to work, but leave little processing power to the rest of the system. Also I'm not sure if I really got up to 5Hz updates. Now I generally use 0.5, which works fine for me.


    Setting to 0.2 would work fine, setting to 0.01 may hog your cpu, your mileage may vary. I generally use 0.5, which means that I can still decently show a clock wich updates at least once per second.
    Why would you want to use such a short sleep time?

    Regards,
    Mark.
    Hi Mark,

    Thanks very much for your detailed reply. It was very helpful. I actually went out in the car and made a measurement of speed and I am confident that GPS speed obtained from positioning module is in [meters/sec] units. Also regarding my questions 3 and 4; I am interested in combining GPS measurements with accelerometer sensor data for a novel navigation related application. The faster I read the sensor data the better it is in terms of my application. I am setting sleep time to 0.01 sec because I want to read the accelerometer data as fast as possible (The highest speed I got is 32Hz-which I obtain at 0.01 sleep time). I am reading GPS sensor and accelerometer sensors in the same loop so this why I asked if it would be a problem set such slow sleep times. I am not an expert Python programmer and I don't know the best programming techniques for this language. Perhaps there is a better way to read the sensors, as seperate threads - though I know nothing about multi-threaded programming.

    Thanks again,

    Selim

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