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Old 09-05-2010, 14:35   #1
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Using Garmin GPS 72

Hello to all.
I own a Garmin (GPS 72).
Using the USB-RS232 cable I have no trouble when sailing: Ship´s position works great....
GPS 72 NMA interface offers the following serial interface format options:
- GARMIN
- DGPS GARMIN
- NMA
- TEXT OUTPUT
- RTCM INPUT
- RTCM INPUT / NMA OUTPUT
- RTCM INPUT / TEXT OUTPUT
- NONE

When at sea and working with satellite inputs all is working correctly (ship´s symbol is RED COLOR)
When I set the GPS in the SIMULATION MODE the ship´s symbol CHANGES course but NO speed (the symbol remains in black color).
I know there´s not big trouble as I can use Open CPN in the "real" job but I can´t imagin what difference it makes SIMULATION vs REAL SIGNALS.
Thanks you all.
Sorry about some word mistakes. My native language is spanish.
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Old 09-05-2010, 18:55   #2
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I was told that the different color in the simulation mode was intended to alert the user that something different was happening in the GPS. As you said, everything works as it is supposed to outside the simulator.
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Old 10-05-2010, 02:40   #3
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Thanks for your reply Mr. Daugherty.
I think I placed my post in the wrong spot.
I intended to say than "using my Garmin GPS 72" with Open CPN software the ship´s symbol changes to RED color with real satellite signals (and works OK). When in Simulation mode the ship´s symbol remains black (and no movement shown).
As far as I know, GPS 72 sends the same NMA protocol sentences in Real and Simulation Modes.
żDoes Open CPN "sees" other data?.
Thanks
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Old 10-05-2010, 05:34   #4
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Quote:
Originally Posted by balsicas View Post
Thanks for your reply Mr. Daugherty.
I think I placed my post in the wrong spot.
I intended to say than "using my Garmin GPS 72" with Open CPN software the ship´s symbol changes to RED color with real satellite signals (and works OK). When in Simulation mode the ship´s symbol remains black (and no movement shown).
As far as I know, GPS 72 sends the same NMA protocol sentences in Real and Simulation Modes.
żDoes Open CPN "sees" other data?.
Thanks
There is a status flag in most NMEA position sentences which indicate whether position data is valid or not. Obviously a simulated position is not valid so the status flag would indicate this. You get a similar status when GPS is first switched on until it receives fix. For reasons of safety I'm guessing that Open CPN detects this & displays accordingly.

Here is an example of status flag in field 2 of the RMC sentence:

for NMEA 0183 version 3.00 active the Mode indicator field is added
$GPRMC,hhmmss.ss,A,llll.ll,a,yyyyy.yy,a,x.x,x.x,dd mmyy,x.x,a,m*hh

Field #
1 = UTC time of fix
2 = Data status (A=Valid position, V=navigation receiver warning)
3 = Latitude of fix
4 = N or S of longitude
5 = Longitude of fix
6 = E or W of longitude
7 = Speed over ground in knots
8 = Track made good in degrees True
9 = UTC date of fix
10 = Magnetic variation degrees (Easterly var. subtracts from true course)
11 = E or W of magnetic variation
12 = Mode indicator, (A=Autonomous, D=Differential, E=Estimated, N=Data not valid)
13 = Checksum
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Old 10-05-2010, 05:58   #5
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Thanks a lot richardhula.
Hey... this forum works real fast .
It seems to be the way you say. Field # 12 (Mode) would be the reason.
I didn´t know (reading my GPS 72 Owners Manual) that fact.
Aparently, Simulation and "real" sentences contain the same data.
You guys are the REAL experts.
Thanks again.
Hope to see you around Cadiz (Spain) one of these days. I have some beers waiting for you.
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