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N6722C avatar image
N6722C asked WombiiActual edited

GPS displaying ILS / VOR data based incorrectly on data from Nav Radio ?

This is going deep down the Rabbit Hole,, but it would seem that some major functions of the GPS are based on the incorrect assumption, that thr GPS relied on data FROM the Nav Receiver, to determine it's display of it's Database information.

Taking on of the simpler Garmin GPS system as an example - ie GNS530

Ref: Garmin Trainer - When the GPS is displaying information about VORs, ILS's, etc, it's should be displaying that data based on GPS information, and NOT from any data that would be got from any Nav receivers.


It should not matter if the Nav radio can pick up one of these Nav Aids or not, the GPS should only display information from it's database.(+ aircraft GPS position)


Example: DIS (Distance) to VOR

This should be the Horizontal distance between the Plane's Position, and the Position of the VOR.

GPS gets Plane position, and then looks up in it's Database the Position of the VOR, and displays the Horizontal distance ( not the slant Range : DME)

It also does not care if that VOR is being received by the Nav Receiver, it is in range or out of range, or even if the VOR is Down, or the Nav radio is OFF. (or of course, tuned to a different VOR frequency !)

If the GPS is told to display the closest VORs, it should search its Database, and list the nearest, with number of VORs displayed limited either by number or physical distance.

If the VOR is Low Altitude, with a short range, and the plane is outside that range, it should still display that VOR, if it meets the Number / physical distance rule.


Currently, if the Nav Receiver cannot receive that VOR, it is ignored in the List.

If it is an ILS, and the plane is outside the ILS cones, then it does not display that ILS - which is also incorrect.

Another Example. A DME (no radial information info)

The Gps should display its Distance AND GPS bearing. It does not care that the DME does not transmit any Bearing information.. once again, its NOT considering a Nav Receiver input, its purely displaying the GPS position of the DME Navaid. Distance and Bearing from the Plane.


In fact, the more one looks at the GNS530, comparing it to the true Garmin (Ref: Garmin Trainer - The Garmin Pilot's manual can be ambigeous on some of this ) , the more the operation of the ASOBO MSFS GNS530 is not following even the basic functionality of the real GPS.


So the questions are:

(1) Am I correct, or have I entered the Twilight Zone.?

(2) If it is in fact the modeling of the Garmin is incorrect, does it matter. ?

(3) Should it be corrected, or left to some 3rd Party Mod to make corrections. ?

buggauges
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WombiiActual avatar image
WombiiActual answered

I'm not sure if I understand what you're saying, because it seems to me this is working correctly, like you're requesting? As long as the GNS430 or the G1000 in the sim is in GPS mode (purple) it is absolutely using GPS database data and not nav radios.

If you switch it to VLOC (green) it uses data from the nav radios.

Direct to a VORDME in GPS mode and it will show ground distance and gps bearing to the waypoint regardless of nav radio frequency or reception. Tune to the frequency and go to VLOC (green) mode and the DME indicator will show the slant distance when in range.

The VORDME shows up in the nearest list even if out of range or covered by terrain.

Seems correct to me based on the Garmin user manual and what you want, if I understand your post correctly.

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N6722C avatar image
N6722C answered N6722C edited

Here is an example of the Distance vs DME issue.

Using the Garmin Trainer as a Reference.


on-ground.png

Plane is on the ground, 0.5 nm from the VOR at the Airport.

GPS Mode (not that it make any difference here)

Tuned to the VOR, so GPS reports the VOR at 0.4 nm DISTANCE

==================


Then Put plane up to altitude 11,500ft approx 2 miles)

GPS still reports 0.4 Miles -- ie DIS is the the Horizontal DISTANCE.

2-miles-high.png


If it were DME, it would report 2 miles.


ie as the ASOBO GNS530 displays ( simvar "NAV DME:index" )

asobo-2nm.png


CONCLUSION

The ASOBO GNS530 reports 2 miles, so the ASOBO GNS is reporting 2.0 nm (which is really DME - Slant range)

while the Ref Garmin Trainer is still reporting the correct DIS = 0.4nm the Horizontal Distance.

The DIS display is the GPS calculated DISTANCE. It is not the DME distance that would come from the nav Receiver.

Nor is it a Calculated Slant range (DME) , as "could" be calculated by the GPS, as it knows both the Plane's and the VOR's Position & Altitude.




on-ground.png (242.2 KiB)
2-miles-high.png (240.8 KiB)
asobo-2nm.png (2.7 MiB)
8 comments
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Thanks for the images, they helped me understand the issue. Seems you're correct that the VLOC Ident window on the 530 is inaccurately represented. I also realised I might not have the 530 in any planes in the standard edition and the 430 doesn't have the VLOC ident window, so I'm not directly affected.

There seems to be an actively developed mod here: GitHub - pimarc/pms50-gns530: Flight simulator 2020 GNS530 Mod that you could check out.


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The screen shots were with the improvements of the GNS530 Mod ...

Unfortunately, for the MOD to correct a lot of these basic design issues, it would need quite an extensive re-write of a lot of the existing Asobo code (by the Mod), or better, by Asobo in the base sim.



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To assist anyone brave enough to attempt this mod in the future: How should the GPS determine what to show in the VLOC ident window when you manually tune a NAV1 frequency?


A: Wait for signal from VOR, get ID, match ID with internal database and use GPS data.

B: Use frequency to search internal database, match with closest station with that frequency even if there is no signal and use GPS data.

C: Something else.

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@hydrastik9488 Can you have a look at this please :)
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N6722C avatar image N6722C FlyingRaccoon ♦♦ ·

Thanks for looking into this :)

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