Rhumb Line Calculations
Thread Starter
Joined: Apr 2007
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From: United Kingdom
Rhumb Line Calculations
I'm trying to remember the formula for calculating the Rhumb line direction between two co-ordinates.
I have the chlong*sin(meanlat) for distance.
Any help much appreciated.
donandrews
I have the chlong*sin(meanlat) for distance.
Any help much appreciated.
donandrews
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Joined: Jun 2004
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From: Reigate, UK
Looks like you've got the formulae the wrong way around - distance = chlong (minutes) x cos (mean latitude) whereas convergence = chlong (degrees) x sin (mean latitude).
Neither of these will give you the rhumb line direction between two points and if you're talking about ATPL level material you won't have to calculate that in an exam.
You may be given two points where the rhumb line direction is implied (e.g. they're on the same parallel of latitude) and you might be asked to calculate the GREAT CIRCLE track (intial, mid-way, and final) between the two.
Is there a specific question you're looking at?
Rgds,
V1R
Neither of these will give you the rhumb line direction between two points and if you're talking about ATPL level material you won't have to calculate that in an exam.
You may be given two points where the rhumb line direction is implied (e.g. they're on the same parallel of latitude) and you might be asked to calculate the GREAT CIRCLE track (intial, mid-way, and final) between the two.
Is there a specific question you're looking at?
Rgds,
V1R
Thread Starter
Joined: Apr 2007
Posts: 2
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From: United Kingdom
Rhumb Line Calculation
Thank you for your response - first posting so made the error in the formula.
My question is, given two sets of co-ordinates, what formula should I use to calculate the bearing or heading between them?
I appreciate it wont come up in the ATPL but I'd very much like to know how to do this.
Many Thanks.
My question is, given two sets of co-ordinates, what formula should I use to calculate the bearing or heading between them?
I appreciate it wont come up in the ATPL but I'd very much like to know how to do this.
Many Thanks.
Super-Friendly Aviator
Joined: Jun 2004
Posts: 424
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From: Reigate, UK
I fear it may involve spherical trigonometry...at least to get to a nice, user-friendly formula! 
Ah, here we go. A quick Google came up with this:-
http://www.movable-type.co.uk/scripts/LatLong.html
It all looks pretty character-building...
V1R
Ah, here we go. A quick Google came up with this:-
http://www.movable-type.co.uk/scripts/LatLong.html
It all looks pretty character-building...
V1R
Joined: Mar 2003
Posts: 437
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From: UK
Isn't this one of those questions to do with convergence between two given Lat/Longs, so therefore you need to find out at which point they want you to give the GCTrk value? (i.e. mid point, finish?) Trying to recall from Gen Nav, but its been a while.
Anyhow, convergence = change longitude x sin (mean lat) but then you have to figure out which way to apply the calculated value, i.e. a positive or a negative on the original trk. Bristol gave you a neat way of sketching it out and measuring it. I'll go back to the manuals and check it out, unless someone beats me to it (which I hope they will...yawn)...
Anyhow, convergence = change longitude x sin (mean lat) but then you have to figure out which way to apply the calculated value, i.e. a positive or a negative on the original trk. Bristol gave you a neat way of sketching it out and measuring it. I'll go back to the manuals and check it out, unless someone beats me to it (which I hope they will...yawn)...
