Manuel Bessler writes:
> Did a little more "research"... (blindly shooting some search requests
> at google)
>
> Something that came up was, the "Lambert Conformal Conic" Projection.
>
> I also had the chance to ask a real airliner pilot. He said that on A340
> and B744, a line on the NDs represents the shortest path between two
> points, ie. a Great Circle route. He also said that on older NDs (A300
> or A310, I forgot which he mentioned) the line is not a Great Circle
> Route.
>
> So, could the "Lambert Conformal Conic" be the projection I am looking for ?
>
> Any help or pointers are appreciated.
You might be thinking too hard about this.
The following seems to work really slick for me (assuming you are
doing smaller area maps or don't care about some distortion as you get
towards the top/bottom of the map. Even if this isn't quite good
enough for your needs, it will get you out of the gate running and you
can come back later and do something fancier.
Pick some ($center_lon, $center_lat) to be the center of your map.
Then calculate $xfacter = cos( $center_lat * $deg_to_rad )
Now set $h = height in pixels of your display and $w = width in pixels
of your display.
You also want a $scale variable that is set to the something like
number of pixels per nautical mile.
Also note that to convert from a degree of latitude to nm, multiply by
60 (i.e. there are 60 nm for every degree of latitude.)
Ok, so you have all that?
Now if you want to draw something on your map (i.e. a VOR) at some
($lon, $lat) just use the following formula:
$x = $w/2 + ($lon - $center_lon) * $deg_to_nm * $scale * $xfact;
$y = $h/2 - ($lat - $center_lat) * $deg_to_nm * $scale;
($x, $y) is the coordinates (in screen space) where you should draw
the object.
This is known to work pretty well over a local area (assuming my
typing is correct, I didn't overlook something, and you can get past
the pseudo-perl syntax.) :-)
Regards,
Curt.
--
Curtis Olson IVLab / HumanFIRST Program FlightGear Project
Twin Cities [EMAIL PROTECTED] [EMAIL PROTECTED]
Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org
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