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  1. #1
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    Java ME - how to recon if Assisted GPS/pure GPS is used (for altitude precision usag)

    Hello,

    How can I, from my Java ME application, recognized if Assisted GPS is used when I am creating location based applications?

    The reason why I ask is that I get the feeling that the altitude precision gets better after the application has been running for a while (not diverting som much from point to point). My theory is that it is when the application don't need Assisted anymore, the precision gets better. Is this assumption correct? If not, how can I recognized when the precision is good enough for my application?

    Regards,
    Niklas

  2. #2
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    Re: Java ME - how to recon if Assisted GPS/pure GPS is used (for altitude precision u

    Quote Originally Posted by nicsoft View Post
    How can I, from my Java ME application, recognized if Assisted GPS is used when I am creating location based applications?
    It is not possible to do this. The mechanism of the location technology is hidden from you by the location provider implementation. You can ask the phone to return a provider that has a specific accuracy as regards altitude information (see setVerticalAccuracy() in the Criteria documentation), but the phone may return a null (to say that no such provider exists).

    In general, Assisted GPS is only used at the very beginning of a session to give you a quick idea of where you might be (generally within 1km to 3km). It normally does not include any vertical measurement.

    - Mike
    NAVTEQ Network for Developers
    The community for developing innovative location-based applications
    http://NN4D.com

  3. #3
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    Re: Java ME - how to recon if Assisted GPS/pure GPS is used (for altitude precision u

    Ok, thanks for the answer!

    I assume it is difficult to do what I want to do... I have to in some way find out how good the precision is before I start to use the vertical data collection. A first drop of 50m spoils the entire purpose of the function. I have tried waiting a number of getPositions, but it's impossible to know how many I should skip before the precision is stabilized.

    One other potential solution could be to not starting to measure before perhaps 3 satellites are utilised. But I assume that it is not possible to find out how many satellites are utilised at the moment, is there?

    Thanks again!

    /Niklas

  4. #4
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    Re: Java ME - how to recon if Assisted GPS/pure GPS is used (for altitude precision u

    Quote Originally Posted by nicsoft View Post
    I assume it is difficult to do what I want to do...
    In Java ME it is not just difficult, it is impossible.

    Quote Originally Posted by nicsoft View Post
    One other potential solution could be to not starting to measure before perhaps 3 satellites are utilised. But I assume that it is not possible to find out how many satellites are utilised at the moment
    You may be able to do this in C++, but not Java.

    Quote Originally Posted by nicsoft View Post
    I have to in some way find out how good the precision is before I start to use the vertical data collection. A first drop of 50m spoils the entire purpose of the function.
    You can ask the device to return a Location Provider that has any accuracy you desire using Criteria.setVerticalAccuracy(int accuracy). You just have to decide what to do if the phone says "I don't have one."

    Bear in mind that the best accuracy you will get is 10m to 20m anyway. GPS works by sending signals from multiple angles so that you can triangulate a position. To make this work for height, you would like to see at least one, preferably more, satellites BELOW your current height. Unless you are in a high altitude aircraft (which don't use GPS for altitude measurement) you will never normally see a satellite as being BELOW you.

    - Mike
    NAVTEQ Network for Developers
    The community for developing innovative location-based applications
    http://NN4D.com

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