Durk Talsma writes:
> 
> I'm trying to solve the following problem:
> Given the following: 
> - latitude, longitude of departure
> - latitude, longitude of arrival 
> - scheduled departure time
> - scheduled arrival time
> 
> I want to calculate the current position of the aircraft , sssuming that it 
> travels along a great circle route between these two points and also assuming 
> that the current time is somewhere between arrival and departure.
> 
> I currently have two questions: 1). Is there already code available in 
> FlightGear or SimGear that can do this for me? I browsed the waypoint and 
> math directories in SimGear, and the route manager files in FlightGear's 
> Autopilot directory, where I found lot's of code to solve parts of the 
> porblem[*], but I couldn't find a full solution yet. 2). Is it possible to 
> translate the solution from a spherical coordinate system to a WGS84 world 
> model? I have a fairly good concept of how I would solve this problem using a 
> spherical world model, but I don't know yet how I should adapt this to a 
> WGS84 model. I need this function for an AI traffic manager that I'm 
> currently writing for FlightGear. 
> 
> [*] Using existing FlightGear/Simgear code, I managed to calculate the 
> distance between two points, which I could then divide by the difference 
> between Arrival and Departure time, to get the average speed of travel. 
> 

see Simgear / math / sg_geodesy.[x]xx

geo_inverse_wgs_84
geo_direct_wgs_84

use the inverse form to determine distance and azimuth of target location
then use the forward form to determine intermediate points from
azimuth found and fractional distances

HTH

Norman

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