Re: [Flightgear-devel] mpmap ILS data

[Peter B. <smo...@ad...>]

On Apr 8, 2010, at 8:08 AM, David Megginson wrote:

> On Wed, Apr 7, 2010 at 10:06 PM, Peter Brown
> <smo...@ad...> wrote:
> 
>> Perhaps this has been brought up before, but I see that the ILS "beam" data for each airport on the mpmap is derived from the runway alignment (as verified in taxidraw).  This doesn't allow for magnetic deviation, and therefore all the course headings are incorrect.  Makes it tough to line up with the ILS, unless you pull info from an outside source (airnav, flightaware, etc) for each arrival airport.
> 
>> Example at KBTV, runway 15 -
>> mpmap ILS course 130.92 degrees
>> Flightaware ILS approach plate, 146 degrees.
> 
> I'm not familiar with mpmap, but that's not a problem for FlightGear
> itself - the localizer directions are all specified in
> Navaids/nav.dat.gz in degrees true, independently of any runways they
> might be associated with (not all localizers are attached to a runway,
> and even when they are, the direction might be 10 degrees off from the
> runway).  Here's the example for BTV (where I've flown the localizer
> in real life as well as in FlightGear):
> 
> 12  44.46520000 -073.14009400    342 11030  18       0.000 IVOE KBTV 33  DME-ILS
> 
> But then, the vast majority of runways don't have localizers.  Perhaps
> the map is just trying to show an extended runway centreline, and the
> person who designed the app mixed up magentic and true heading.  The
> Airports/apt.dat.gz file does give runway headings in degrees true,
> not degrees magentic, so there's no need to mess around with magnetic
> deviation.
> 
> 
> All the best,
> 
> 
> David
> 
> 

David, yes, as I have as well.  The localizer for 33 as you listed above is on a 326 heading per the approach plate, but the mpmap shows ILS data as the runway heading in degrees - as if for users to use as the ILS data.  I'm not sure what the 342 in the navaid file is referring to unless it's elevation?... elev. is 335, course is 326.  (ref: http://flightaware.com/resources/airport/BTV/IAP/ILS_DME+RWY+33/pdf)
I believe James is correct in that it's probably a question for Pigeon, whom I believe created and maintains the mpmap data.


James,
You are correct as well, in real life you don't shoot an approach without the plate.  (Okay..., you shouldn't...)   :)  But....FG does have to walk that thin line between sim and reality, and until users get to the point of full reality immersion, they will use the data presented to them for ease of use (if nothing else).  While I enjoy FG immensely due to all of the developers work, I doubt I'll be strapping on an approach plate until I'm sitting in a full blown simulator cockpit with the door shut.  :)

So, I guess I'll see if Pigeon responds about perhaps re-formatting the mpmap code to use actual approach headings instead of runway headings.  For anyone that isn't aware of the data presented, I recommend you take a look.  It has more info than you may realize, and it helps the user find airports, navaids, and more.  Airport data includes the degree of GS (for those rare abnormally high approaches), localizer frequency, and if a CAT 1,2, or 3 approach.  For most of the users this is a wealth of information.

A side benefit is from an ATC point of view for FG events, you can visually see how well the pilots are flying the localizer.

Peter :)