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GPS MISCONCEPTIONS

Discussion in 'Phantom 2 Vision + Discussion' started by CapnBob, Dec 18, 2014.

  1. CapnBob

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    There seems to be a popular misconception that GPS satellites are geostationary.
    Unlike TV sats (DirecTV, Dish, etc.) GPS sats are not geostationary, or "hovering" over the same spot on earth, they move around the planet.
    As they orbit, the number of birds in view at any spot on the planet naturally fluctuates with time.
    This is exacerbated because the planet is also rotating under the sats.
    As of last year, there had been 68 GPS birds launched compared to the original 24, so coverage is getting better.

    If you take a reference, and do nothing but wait an hour and then take another reference, you will normally indicate a different number of birds.

    This is why I see some frustration in these forums. Some claim a "fix" because they took a reference, did something, and then their number went up, while others are puzzled, because they did the same thing and their numbers went down. Elapsed time is generally the culprit.
    Day-to-day measurements in one spot will see variations in the number of sats available.
    Now throw weather, sunspots, RFI, multipath reflections, and a lot of other variables into the mix.

    In a perfect scenario, you would always get enough sats to fly, but very few of us have a horizon-to-horizon field of view.

    This gif indicates a "normal" fluctuation over time at 45° Latitude. Watch the blue spot on the globe as it goes through the day; you will see a variation between 6 and 12 sats as a norm. However, where you are, and your surroundings have a huge impact. OR: "Your mileage may vary".
     

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  2. happydays

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  3. Mako79

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    they should have stolen the Russian sats and added glonass for redundancy..
     
  4. CapnBob

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    Nice vids, Connor.
     
  5. happydays

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    Why thank you Cap'n. Crap weather here so not much chance of getting out. And work gets int he way too...
     
  6. msinger

    Approved Vendor

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    Anyone know of an app/website that will show the current satellite count by position (latitude/longitude)?
     
  7. CapnBob

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    Try here. Time slider follows orbits

    http://in-the-sky.org/satmap.php
     

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  8. Chuck26287

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    If you're using iOS, search the Apps Store for "P-Track" or "GPS Plan". As for a website, look at http://satpredictor.navcomtech.com.
     
  9. happydays

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    GPS plan works well on iOS
     
  10. msinger

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    "GPS Plan" is a keeper. Thanks for the recommendation!
     
  11. jadebox

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    In a geosynchronous orbit, the satellite orbits once for every rotation of the earth under it. Not all geosynchronous orbits are geostationary where the satellite is over the equator and stays above the same spot on the earth throughout its orbit.

    GPS satellites are in a type of synchronous orbit known as a "semi-synchronous" orbit. In a semi-synchronous orbit, the satellite orbits twice for every rotation of the earth.

    -- Roger
     
  12. CapnBob

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    Yes, the correct term for the Comm Sats is "geostationary". Hadn't had my coffee yet.
     
  13. IrishSights

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    GPS Test app for IOS and Android. Cleanest nifty app I've seen for this. Does Glonass as well if device supported it.
     
  14. CapnBob

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    This is very good, you can put in your location, and see hour by hour service.

    http://satpredictor.navcomtech.com/
     
  15. PB30X

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    I use my Garmin Rino (GPS) radio when out and about just because of cell reception loss in secluded areas.. Very accurate!!
     
  16. Meta4

    Meta4 Moderator
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    Rather than apps that show what sats are theoretically above you if you had a perfect horizon, wouldn't you be better off using an app that shows what sats your device can detect. On Android GPS Status is ideal. https://play.google.com/store/apps/deta ... tus2&hl=en It uses the phone's GPS sensor to display the sats it can read and their signal strength.
    There must be something similar for IOS
     
  17. ianwood

    ianwood Taco Wrangler
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    An even bigger GPS misconception is that the Phantom's GPS is the cause of many flyaways. I can't speak for the P1 but I'm pretty sure the number of P2 flyaways caused by GPS is roughly 0.
     
  18. Prylar Bek

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    Then what do you attribute all these flyaway to?
     
  19. Prylar Bek

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    WRONG...there are folks who do follow and read the manual and still have flyaways...I figured you would have an asanine comment and you didnt disappoint! Besides the question wasn't directed at you it was for the OP...why don't you go troll somewhere where your comments are more valued.
     
  20. Prylar Bek

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    So, you are saying to the dozens,if not 100's of people on this site that their flyaways are happening because they didn't understand the various modes work or relying on RTH? BULL ****. You are a self proclaimed 'expert 'and are totally discounting the clear evidence that has been posted here by people who HAVE read and understood the manual and the various modes. People had flyways that had nothing to do with RTH.Why don't you read some of their experiences before you knee jerk your dumb *** and condescending comments and you will see that RTH was not an issue with flyaways!