Results 1 to 13 of 13
  1.    #1  
    So, I use my GPS all the time (typically for GolfPinFinder -- awesome app!) and it works great (with occasional hiccups).

    However, while driving today I was using the GPS Dashboard Free version that reports your speed, direction and altitude. Speed and direction were right on, but the altitude is **WAY** off.

    I compared this to the GPS in my car and it was off by about 150 feet. So then I looked up the altitude of the local airport drove there an my car GPS was almost right on (off by a couple feet), but my Pre was still off by around 145 feet.

    So, I started thinking it was the GPS Dashboard Free app that was doing the calculation wrong. I tried doing ##477# and got a fix and the altitude that it was report there was incorrect too!! Of course that altitude is shown in meters, but a simple conversion showed it was off the same. The fix said the error for both horizontal and vertical was 3 meters.

    What gives? Anyone else notice that altitude is off too?
  2. moserjj's Avatar
    Posts
    468 Posts
    Global Posts
    470 Global Posts
    #2  
    What was your altitude reading over by the airport? My office is right off Melby, 2 blocks from there (assuming you're profile location is accurate and you're talking EC, WI) and I too was trying out GPS dashboard (to record my bike rides to work). Was about 850ish for the accuracy, didn't bother to see if that was accurate or not. I've got several devices, I'll try them tomorrow and see if there are any discrepancies.
  3. #3  
    I actually noticed the exact same thing a few months back. I live right on the shoreline, so I know that I'm almost exactly at sea level; but when I fired up GPS Dashboard Free, it was giving me a completely incorrect altitude reading. I assumed the same thing, that GPS Dashboard Free was calculating incorrectly and gave the app up for a bad job.

    Its an interesting issue... I wonder if it could have anything to do with the Pre using aGPS rather than standard GPS. I know there is a hack out there that allows you to use GPS without the tower assist. I would be interested to see if the reading would be any different in that case.

    Anyone out there using a pre thats modified to run GPS rather than aGPS? If so, hows your altitude accuracy?
  4.    #4  
    Quote Originally Posted by moserjj View Post
    What was your altitude reading over by the airport? My office is right off Melby, 2 blocks from there (assuming you're profile location is accurate and you're talking EC, WI) and I too was trying out GPS dashboard (to record my bike rides to work). Was about 850ish for the accuracy, didn't bother to see if that was accurate or not. I've got several devices, I'll try them tomorrow and see if there are any discrepancies.
    Yes, that is Eau Claire, Wisconsin. However, right now I am in Bloomington, Il.

    I'm proud to know that you live there and have developed such an AWESOME app!!!
  5. #5  
    Quote Originally Posted by Mikey47 View Post
    So, I use my GPS all the time (typically for GolfPinFinder -- awesome app!) and it works great (with occasional hiccups).

    However, while driving today I was using the GPS Dashboard Free version that reports your speed, direction and altitude. Speed and direction were right on, but the altitude is **WAY** off.

    I compared this to the GPS in my car and it was off by about 150 feet. So then I looked up the altitude of the local airport drove there an my car GPS was almost right on (off by a couple feet), but my Pre was still off by around 145 feet.

    So, I started thinking it was the GPS Dashboard Free app that was doing the calculation wrong. I tried doing ##477# and got a fix and the altitude that it was report there was incorrect too!! Of course that altitude is shown in meters, but a simple conversion showed it was off the same. The fix said the error for both horizontal and vertical was 3 meters.

    What gives? Anyone else notice that altitude is off too?
    i dont believe so... this was in mid air...
    Attached Images Attached Images


    thank you mytether
  6.    #6  
    Quote Originally Posted by jonathanlc2005 View Post
    i dont believe so... this was in mid air...
    That's cool, didn't think it would work in mid-air like that in a jet.

    However, the error that I am talking about is around 150 feet. You really would not be able to tell there is a 150 foot error while riding back in the seats of a jet. Now if you took it up to the pilot and asked for his altimeter reading .
  7. #7  
    GPS altitude can be tricky --

    Altitude Accuracy

    And an interesting experiment --

    GpsPasSion Forums - * Altitude Comparison *

    Dave
  8. #8  
    Quote Originally Posted by zeakthegeek View Post
    Its an interesting issue... I wonder if it could have anything to do with the Pre using aGPS rather than standard GPS. I know there is a hack out there that allows you to use GPS without the tower assist. I would be interested to see if the reading would be any different in that case.

    Anyone out there using a pre thats modified to run GPS rather than aGPS? If so, hows your altitude accuracy?
    This.

    http://forums.precentral.net/palm-pr...ed-cached.html

    More specifically, could those of you, who believe you're having problems, modify your Pre to use standalone GPS rather than aGPS?? ... and then report back with your findings here?

    I'm almost positive that it'll help your situation out. I can't tell how it affects altitude accuracy, honestly, because mine's already been modded and I'm not going back.
  9.    #9  
    Quote Originally Posted by sparksd View Post
    GPS altitude can be tricky --

    Altitude Accuracy

    And an interesting experiment --

    GpsPasSion Forums - * Altitude Comparison *

    Dave
    Thanks sparksd!! Altitude is just an interesting side note for me with GPS, my vehicle usually stays in constant contact with the ground so altitude is not that important.

    What I though was funny was this quote from the second link you provided:

    Quote Originally Posted by SomePersonOnOtherBoard
    One thing is clear from this little test. To all those pilots who have asked in the forums about using these consumer GPS units for altitude readings - DON'T DO IT. I used to fly gliders at one time and I clearly would not want to rely on this type of data in a critical situation. For the rest of us, altitude readings are fun, but that's about it.
  10. #10  
    Mine's been off ever since I first cared to look. When I'm driving along the QEW on the southern shore of Lake Ontario it always says that I'm around 45m, but Lake Ontario itself is already 75m so the highway on shore should be even more than that.

    I've just always figured it's something in the math that makes altitude harder to calculate accurately than position. From a triangulation perspective (which I know isn't really how GPS works) satellites are found in any direction (360 degrees) on a ground plane but only 180 degrees in a vertical plane, probably 120 at best in the real world of buildings and tree lines. That's a lot less variation to calculate against...
    Yeah, uhh... it's Kevin. (KevinT was already taken.)

    PalmPilot Professional, Palm V, Kyocera 7135, Treo 600, Treo 650, Treo 700p, Palm Prē & Prē 2, HP TouchPad & Veer
  11. #11  
    Sounds like they are using different representations of the shape of the earth. Many standalone GPS provide height above the reference ellipsoid and also height above mean sea level (MSL). Both are an approximation normally done to minimise error accross the globe. The OS guide linked below has a pretty good explanation. There is no difference between assistedGPS (aGPS) and normal standalone GPS in this regard.

    Welcome to OS Net
  12. #12  
    Well, in the thread I linked to above... I thought that some people mentioned they get more satellites to "lock-on" to.

    If that is the case, which I think it is... standalone GPS would most definitely give you SOMETHING better than aGPS, which requires a data connection. What kind of accurate GPS device requires a cellular data connection?

    Again... not saying that the altitude won't be way off... but it should be MORE accurate then leaving the stock restrictions be that your carrier applied to your device.
  13. #13  
    aGPS just give it a kickstart to improve the time to first fix and indoor sensitivity. The height discrepancy is just the reference ellipsoid being used.

Posting Permissions