Garmin GTN650 user flight plan import question

Juergen Mentor

Well-Known Member
Hi Everyone,

I'm trying to find a way to import a grid built on a computer to a Garmin GPS device that will in turn drive an autopilot. While possible in the 430W/530W the problem is that Garmin tech support was unable to help me determine whether it was possible in any of their newer radios. So I'm hoping someone here has access to a GTN650 or has the knowledge with the system that I lack.

Background on the GNS430/GTN650 flight plan import formats:

You can define a user Longitude and latitude in a 650 flightplan but it is limited to Degrees Minutes and tenth of minutes (DD MMM.m). On the 430 it's in Degrees decimal degrees (DDD.ddddd). The problem is that while the 430 allows me to have an precision of 5 decimal places (if this were a point on a map it would be a circle with a diameter of 1.1 meters) ... the 650 only lets me have a single decimal place in it's minutes ... leading to a precision of 180m (If this was a point on a map, it would be a circle with a diameter of 180 meters). A huge difference in precision ( This information was determined using this data http://wiki.xkcd.com/geohashing/GPS_accuracy ).

Despite feeling as though all was lost I continued to read the specification sheet which further explained you could import user waypoints using a waypoint file which allowed you to define a point using Degrees decimal degrees (why the lack of consistency the world may never know). Additionally you could have up to 9 decimal places or DDD.ddddddddd. Possibly overkill? That exceeds the capabilities of GPS ... as far as I am aware of. That aside this would allow the precision required.

And now the main question. How do I define a flight plan to be imported that uses user made waypoints in a user.wpt file to define a route in a plan.gfp file.
The manual doesn't specify a way to refer to the user waypoints and the ones they defined in the user made flight plan file don't have names so they aren't referenced that way.

Examples:

Route file: FPN/RI:F:KSLE:F:N45223W121419:F:N42568W122067

a quick break down:
FPN/RI - required at start of flight plans
:F: - Flightplan segment identifier
KSLE - Airport identifier. Can also be a VOR, Fix, etc.
N45223W121419 - N 45 degrees 22.3' / W 121 degrees 41.9'

Which is all well and good except for the whole single decimal place in the waypoints.

The waypoint file is a CSV that looks like:

MTHOOD,MT HOOD PEAK,45.3723,-121.69783
CRTRLK,CRATER LAKE,42.94683,-122.11083
EIFFEL,EIFFEL TOWER,48.858151,2.294384


Each line is a waypoint. Each data point is seperated by a comma. The format is: Waypoint name, Waypoint description, Latitude, Longitude

So can I first import the user.wpt above and then create a flightplan stating:
FPN/RI:F:KORD:F:MTHOOD:F:CRTRLK:F:EIFFEL import that afterwards and have it work? Would anyone with a GTN 650, some extra spare time and a heart of gold be willing to test this out?

Hopefully someone will be able to get me back on the right track. This is a bit of tricky problem to solve and an even harder one to do with no hardware available.

Thanks to anyone who can provide input.

P.S. The flight plan file format manual is attached
 

Attachments

somewhereupthere

Well-Known Member
Hi Everyone,

I'm trying to find a way to import a grid built on a computer to a Garmin GPS device that will in turn drive an autopilot. While possible in the 430W/530W the problem is that Garmin tech support was unable to help me determine whether it was possible in any of their newer radios. So I'm hoping someone here has access to a GTN650 or has the knowledge with the system that I lack.

Background on the GNS430/GTN650 flight plan import formats:

You can define a user Longitude and latitude in a 650 flightplan but it is limited to Degrees Minutes and tenth of minutes (DD MMM.m). On the 430 it's in Degrees decimal degrees (DDD.ddddd). The problem is that while the 430 allows me to have an precision of 5 decimal places (if this were a point on a map it would be a circle with a diameter of 1.1 meters) ... the 650 only lets me have a single decimal place in it's minutes ... leading to a precision of 180m (If this was a point on a map, it would be a circle with a diameter of 180 meters). A huge difference in precision ( This information was determined using this data http://wiki.xkcd.com/geohashing/GPS_accuracy ).

Despite feeling as though all was lost I continued to read the specification sheet which further explained you could import user waypoints using a waypoint file which allowed you to define a point using Degrees decimal degrees (why the lack of consistency the world may never know). Additionally you could have up to 9 decimal places or DDD.ddddddddd. Possibly overkill? That exceeds the capabilities of GPS ... as far as I am aware of. That aside this would allow the precision required.

And now the main question. How do I define a flight plan to be imported that uses user made waypoints in a user.wpt file to define a route in a plan.gfp file.
The manual doesn't specify a way to refer to the user waypoints and the ones they defined in the user made flight plan file don't have names so they aren't referenced that way.

Examples:

Route file: FPN/RI:F:KSLE:F:N45223W121419:F:N42568W122067

a quick break down:
FPN/RI - required at start of flight plans
:F: - Flightplan segment identifier
KSLE - Airport identifier. Can also be a VOR, Fix, etc.
N45223W121419 - N 45 degrees 22.3' / W 121 degrees 41.9'

Which is all well and good except for the whole single decimal place in the waypoints.

The waypoint file is a CSV that looks like:

MTHOOD,MT HOOD PEAK,45.3723,-121.69783
CRTRLK,CRATER LAKE,42.94683,-122.11083
EIFFEL,EIFFEL TOWER,48.858151,2.294384


Each line is a waypoint. Each data point is seperated by a comma. The format is: Waypoint name, Waypoint description, Latitude, Longitud
First, accuracy will depend on latitude, as distance between lines of longitude change with latitude. At 80N the distance between lines of longitude is 19393 meters. 60 minutes in a degree makes is 323.21666 meters per minute, so .1 minute would be 32.322 meters. At 30 degrees latitude this would be 160.81 meters between tenths of longitude minutes.

Now, distance between lines of latitude generally remain constant. At 80N it's 111659.88 meters, and at 30N it's 110852.42 meters. This makes distance between minute tenths 186.1 meters and 184.75 meters respectively.

Now, on to the other issues:
So can I first import the user.wpt above and then create a flightplan stating:
FPN/RI:F:KORD:F:MTHOOD:F:CRTRLK:F:EIFFEL import that afterwards and have it work? Would anyone with a GTN 650, some extra spare time and a heart of gold be willing to test this out?

Hopefully someone will be able to get me back on the right track. This is a bit of tricky problem to solve and an even harder one to do with no hardware available.

Thanks to anyone who can provide input.

P.S. The flight plan file format manual is attached
No, I would think not because:

The manual says user defined waypoints are DDMMm, and are specified without a name, and that the GTN matches the user waypoints (I assume by lat/long) in the imported flight plan with those in the user waypoint database, and if not stored in the user waypoint database, a generic name is assigned to each waypoint.

The manual then tells you the following:
Note: If a waypoint to be imported is located within 0.001° (latitude and longitude) of an existing
user waypoint in the GTN, the existing waypoint and name will be reused.
I would assume that when you load a flightplan, it cross references the lat/long of the user waypoint in the flightplan to those in the user waypoint CSV file. If a waypoint is found within .001° latitude and longitude of the lat/long defined in the flightplan, the GTN says "Thats the intended waypoint"

The issue for you is going to be batch converting decimal.degree from the CSV to the DDMM.m format. ie: If you can do this without a lot of work.

The accuracy of .001 degrees again depends on latitude and longitude given, but using the 80N 30N example, it will be between 19.4 meters and 96.5 meters distance east/west and 111.7 meters 110.9 meters distance north/south.

Given the accuracy of DDMMm, chances are that the lat/long in the flightplan will easily be matched to a user waypoint in the CSV file, so long as the user waypoints are separated by say at least 120 meters or 400 feet.

Forgive any errors with the math as it was done quickly and without double checking
 
Top