I don't know how much you know about the more technical geeky things, but I was thinking (this isn't usually a good thing) about it and had a thought. If you have a handheld GPS that outputs NMEA (most do) and know how to make a microcontroller do what you want it to, you could concievably build it yourself. It's a little beyond my current level of geekdom (mostly because I'm on painkillers and haven't messed with C++ in a couple of years), but now I'm interested and might have to make this work. I just connected to my eMap with Hyperterminal and here's one frame:
$GPRMC,233646,V,3024.7621,N,09534.2243,W,0.0,0.0,201007,3.9,E,S*0F
$GPRMB,V,,,,,,,,,,,,A,S*0E
$GPGGA,233646,3024.7621,N,09534.2243,W,8,09,2.0,95.7,M,-24.0,M,,*4F
$GPGSA,A,3,02,04,05,09,10,12,17,28,30,,,,3.6,2.0,3.0*31
$GPGSV,3,1,09,02,72,293,50,04,54,031,48,05,23,317,42,09,24,251,42*7B
$GPGSV,3,2,09,10,25,179,43,12,41,316,46,17,27,082,44,28,07,144,36*7F
$GPGSV,3,3,09,30,07,321,36*41
$GPGLL,3024.7621,N,09534.2243,W,233646,V,S*5D
$GPBOD,,T,,M,,*47
$PGRME,15.0,M,22.5,M,27.0,M*1A
$PGRMZ,314,f,3*1D
$PGRMM,WGS 84*06
$GPRTE,1,1,c,*37
If you look close at all that apparent randomness you'll see some interesting things like lat/long coordinates, map datum, and other mostly useless (for this discussion) stuff. What's of interest here is this:
$GPRMC,233646,V,3024.7621,N,09534.2243,W,0.0,0.0,201007,3.9,E,S*0F
In English:
23:36:46 UTC (clock isn't right since the GPS isn't actually seeing satellites in here)
Status= Void (dunno what that means)
Latitude (3024.7621 N)
Longitude (09534.2243 W)
Groundspeed in knots
Track angle in degrees
Date (20th of October, '07. I've been using my other GPSes more lately)
Magnetic variation (3.9 deg E)
GPS Mode= S (simulator, since I'm inside)
And everything after the * is checksum data
So, very basically, we'd just need to write some code that reads the first part of each sentence, waiting for $GPRMC, then parse that line by commas and write the stuff between the 7th and 8th commas into a variable and wait for the next $GPRMC. The next function would convert that variable to MPH (or KPH, or leave it knots if you like), and format it for whatever display device you want. Personally I think I want a 2 digit (0-99) 7 segment LED array arranged upside down so it will look right when it's reflection is seen in the windshield.
But that's all my brain can handle for tonight. My wife thinks I'm nuts for sitting here with a GPS stuck to the monitor and a bunch of strange numbers and letters scrolling down a window. I'll mess with it more when my brain wakes up
Oh yeah, one other thing I'll add mostly so I remember to look into it more tomorrow. There's route data in there, too, which could be fed into an autopilot.
Ok, more more other thing. I'm pretty sure the GPS mice, at least the old serial port versions, just spit out the same NMEA sentences. If so, one could be plugged in instead of a handheld with the same results.
ETA- Duh, forgot one of the things I had planned to say before writing a book. Pitot systems work on pressure differentials. The lower the range of differential pressures, the less accurate they are. It's a resolution issue, basically.
