Hi all

 

FS9 code in gauge for FSX

 

Using CalcGeoCalcLength for PBD calculation and it's working OK for distances around 40 nmls but any thing over 70 I get problems. Is CalcGeoCalc a flat word calculation or great circle distance.

 

Does anyone have an additional formula for great circle distance.

Paul,

 

 Never tried the GeoCalcLength as an input.. ( Yet )  Pages 180 - 183 of this dandy handbook may help..

 

It looks like it is great circle, according to handbook. 

 

Some other topics that "may" help too -

http://www.fsdeveloper.com/forum/threads/mark-position-geocalc-reciprocal-runway.430187/

http://www.fsdeveloper.com/forum/threads/mark-position.430178/

 

There is also the formulary -

http://williams.best.vwh.net/avform.htm

 

Hi Roman

 

GeoCalcLength works as advertised. I think I know why I can't get the values to match. I have a vertical brg. 3 degrees from EOD fix to a TOD fix and I the brg. line is straight should it not curve in relation to earth over a descent distance between the fixes of 80 mls.?

Wonder how they do that at Honeywell.

 

I can send you a copy of code if needed

Paul,

 

 Forgive me if I don't understand what you're trying to get at.. 

Is it - You have the EOD location and altitude and you want to calculate the TOD location (PBD) given a 3* descent rate?

 

If so I would use trig rather than any GPS function to get the distance. A vertical bearing should not be used in the GPS GeoCalc, just horizontal.  The curved distance over a 80 mile straight length would be rather small. 

<!-- Alt in feet in feet or meters. Distance from EOD fix = -->
EOD Dis = (Aircraft ALT - EOD ALT) / Tan(3)
<!-- If in feet convert to meters ( * 0.3048 ) -->

EOD Lat (>c:fs9gps:GeoCalcLatitude1, degrees)
EOD Lon (>c:fs9gps:GeoCalcLongitude1, degrees) 
EOD Dis (>c:fs9gps:GeoCalcLength, meters)
Bearing from EOD (true) (>c:fs9gps:GeoCalcAzimuth1, degrees) 

TOD Lat = (>c:fs9gps:GeoCalcExtrapolationLatitude, degrees)
TOD Lon = (>c:fs9gps:GeoCalcExtrapolationLongitude, degrees)

Hi Roman

 

I got the geocalc all OK and using trig for the vertical brg. but the 3 deg. line FROM THE EOD is about 450 ft. to low at the TOD.

 

May have to reverse it and start at the TOD but lots of thing to change in the FMC display.

 

I understand the Geocalc distance is great circle distance and may have to convert my distance to descend to great circle too.

 

Thanks for your help.

Paul,

 

Ahh   You should be able to do it following the formula for arc length (s) here - http://en.wikipedia.org/wiki/Circular_segment

It will probably still be off because the ALTs are at right angles to the lat/lon, one of which you are trying to find in the first place. 

 

c=(Aircraft ALT - EOD ALT) / Tan(3)   ( in meters)

R=6366707  meters

 

R * (dgrd (arc(cos((R sqr) + (R sqr) - (c sqr)) / 2(R sqr))) (>c:fs9gps:GeoCalcLength, meters)

 

I wonder how FS will handle large numbers like this.. May have to use your own units, 10K meters for instance, then convert back. 

 

Just an idea -

My head hurts... 

Good luck

 

Roman

Hi Roman

 

probably still be off because the ALTs are at right angles to the lat/lon, one of which you are trying to find in the first place.

 

Good point I never thought of that. I got the ground distance sorted and will start the decent point slightly before the predicted TOD in the FMC code to get an overlap.