GPS Satellites 

... they don't fly over the North Pole.

As I write this, today is the 29th Jan 2003. Here's a plot of GPS satellites that have orbited overhead over the last 8 hours:

Its like a time exposure of the Garmin Etrex satellite view.

Actually it's a bit of C# .NET code I'm playing with.

I parse the NMEA $GPGSV frame and plot the results. I get a similar plot as the Etrex - so my code must be close.

Rendering key

Big grey blob - strong signal. Black - current position. Small blob - no signal.

VOID a BUG?

I was bemused to see the "void": the near circular area that satellites fear to tread. I assumed, initially, a bug in my code. 

My latitude is 52N. The hole appears just above the origin... must be a maths bug...

No, not a bug. Its those satellites! Their "Inclination" orbital parameter is close my latitude of 52N.

Put crudely - they don't fly over the North Pole.

Some Parameters

On Jan 2003 these satellites were near overhead some point in the day:

Vehicle GPS ID Inclination
GPS BII-08  21 56.1871
GPS BIIA-10 23 56.4006
GPS BIIA-26  10 56.2101

Orbital period 718 minutes.

XRAY

I seem to be slowly building up a "x-ray" of my house with the GPS struggling to get signals.

Weak signals are seen where item obscure: cold water header tank ENE elevation 40. PC monitor 3 ft west of the GPS. Stronger signals are directly south where there is a window. 

Links

This maps the GPS satellite number to the vehicle number.

http://www.city.yokohama.jp/yhspot/ysc/NAVIGATN.TXT

and this emulates a view from space:

http://liftoff.msfc.nasa.gov/RealTime/JTrack/3D/JTrack3D.html

I have a Bluetooth GPS too!