GPS lock-on time and accuracy

Discussion in 'Questions (Windows Mobile)' started by alfcen, Oct 29, 2007.

  1. alfcen

    alfcen Well-Known Member Licensed User

    Hi Erel
    A user feedback about my B4PPC GPS applications:
    - It takes much longer to get a lock than the other software we were trying.
    - Accuracy 9-25m out on Google Earth. The Garmin was most accurate with +/- 4m.

    I have no statistical data I could provide you with, but if it is not too much trouble, could you please review the gps.dll, in particular the conversion to decimal GPS values?

    I am forced to confirm that, for instance, VisualGPSCE gets a faster fix on GPS than any of my apps in B4PPC.

  2. derez

    derez Expert Licensed User

    GPS lock on time

    Isn't lock on time a function of the GPS reciever that is embeded in the device ?
    I think that all the GPS applications just use the same output stream coming from the reciever, so there sould not be any difference in lock on times.
  3. alfcen

    alfcen Well-Known Member Licensed User

    Yes, David, essentially it depends on the receiver hardware.
    In addition, it is reasonable to assume that decoding of a GPS stream
    in conjunction with the GPS_Decoded event in the gps.dll could
    take influence. Without in-depth knowledge about the dll, this is
    just a theory of mine. Well, a check won't harm, if it doesn't take
    too much time.
    Thanks a lot for your concern.
  4. Erel

    Erel Administrator Staff Member Licensed User

    It is the gps role to get the lock-on.
    When you open the gps port it starts searching for the satellites (if the gps was turned off).
    Maybe other applications first turn on the gps so it will be able to get a fix faster.
    I've checked the decimal values conversation and didn't find anything wrong.
  5. alfcen

    alfcen Well-Known Member Licensed User

    Thanks a lot for your prompt confirmation, Erel.
  6. Scubaticus

    Scubaticus Active Member Licensed User

    Is WAAS enabled on your Garmin? On my one it is and is much more accurate than my CF GPS (don't know if it has WAAS and if so how to enable it through B4PPC.)

  7. alfcen

    alfcen Well-Known Member Licensed User

    Thanks a lot for your concern, Scubaticus

    My user appears to have a Garmin, I don't. As far as I am aware he has a SIRF chip in it. I am not really familiar with most recent GPS receivers, nor do I no what WAAS is. Sorry for my ignorance.

    I asked Erel to check the gps.dll just to rule out errors in the software driver. Everything else depends on the receiver.

    I have a 12-ch CF type GPS receiver which is out a few meters to a few tenths of meters, but delivers better accuracy if you wait a few minutes after the first fix before recording data. For raw GPS data without additional computations, I trust this is quite normal.

  8. Scubaticus

    Scubaticus Active Member Licensed User

    Here is a nice link concerning WAAS.

    I think the more sats. de GPS device sees, the more accurate. I also saw a difference of approx. 250 meters when entering the GPS coords in G-Earth but didn't figure it out yet as I don't use my CF GPS numbers in G-Earth yet.

    There was only a small difference between the values B4PCC on my CF GPS gives me and my Garmin eLegend. with the same difference of position in G-earth.

    When I transfer my data from the garmin and import it into G-Earth, everthing is ok. Not sure why or what, but figure it out some time.

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