Heading in degrees is included in the standard NMEA output strings.  It can
also be calculated from two GPS coordinates (current position and previous
position).  This is why one of the previous posters mentioned that you must be
moving for GPS to work.

Eric


On Tue, 20 Apr 2004 09:11:06 +0200
Ake Hedman <akhe@EUROSOURCE.SE> wrote:

> How do you get the compass info form the GPS?
>
> /Ake
>
> -----Ursprungligt meddelande-----
> Fran: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]For John Tserkezis
> Skickat: den 20 april 2004 03:22
> Till: PICLIST@MITVMA.MIT.EDU
> Amne: Re: [EE:] Mounting a compass sensor in a car
>
>
> PicDude wrote:
>
> > Not surprisingly, when running a compass sensor in my car, I'm running
> into
> > interference (incorrect sensor outputs) from all the other electronics
> and
> > metal in the car.
>
> > Anyone know where these sensors are typically mounted in a vehicle?
>
>   Short answer:  Use GPS, you need to be moving, but it's a small price
> to pay.
>
>   Longer answer:
>   Basically, it should be mounted anywhere where it will work within the
> calibration limits of the compass.  If it doesn't have calibration
> adjustments
> (mechanical or electronic) don't even try using it.
>
>   My magnetic compass came with instructions to point the vehicle to
> north
> (using other known methods) some distance from any surrounding metal,
> overhead
> wires etc, then go though the calibration adjustment (point NSE & W)
> till it
> reads correctly.
>
>   I had it down to within a few degrees.
>
>   In use, it was a different story.  Every time you remove or install a
> piece
> of equipment in your vehicle, you have to check it doesn't interfere
> with the
> compass, and re-calibrate if it does.
>
>   While sitting at traffic lights, the adjacent lane (if moving) would
> cause
> the compass to swing back and forth each time a car passed me.
>
>   While driving in a steady straight line on the freeway (no other
> surrounding
> cars) the compass would sometimes swing back and forth due to
> surrounding steel
> barriers and such.
>
>
>   In the end, I found it so useless (because I couldn't guarantee the
> "purity"
> of my environment where I needed it) that I relied on GPS only.  The
> compass
> was for backup just in case GPS went down.
>
>   Now, if I need backup, I carry two GPS recievers.
> --
>        -o)
>        /\\    Message void if penguin violated
>       _\_V    Don't mess with the penguin
>
> Linux Registered User # 302622
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>
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