05-27-2008, 07:15 PM
|
|
Regular 'Geeker
Offline
|
|
Join Date: Feb 2007
Posts: 431
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
|
|
Re: Why Does GPS work fine one day and not the next?
i have promised to try this but havent got to it yet. a few said it it works
Quote:
Originally Posted by JOLLYROGER
And now some final notes about slow satellite tracking (GPS 101 if you will...):
All GPS units store information about the GPS satellite constellation. These are not geo-synchronous satellites like DirecTV or Sirius Radio. They are in lower orbit and are constantly moving.
Once locked on, the GPS satellites move in and out of visibility, the GPS stores a running log of when and where it last saw a particular satellite allowing it to more accurately predict when it will see that same satellite again and approximately where that satellite will be in orbit at that time. The more accurately a GPS can predict a satellites location, the quicker it will lock on to it.
Since the entire constellation cycles every few hours, I left my phone sitting docked on the cradle over-night running Google Maps in GPS mode in order to let the GPS unit build up a good solid almanac of the constellation. This morning I'm consistantly able to track 7-9 satellites at any given moment and it only takes seconds to lock on after exiting the program. This includes hard resets, soft resets, standby mode, etc.
All that said, the longer you let your GPS run, the better it will get. Conversely, since the satellites do shift orbit somewhat, the longer you let your GPS sit between uses, the more out of date your almanac becomes, and the longer it will take for that initial lock on.
|
|