Using map coordinates
02-08-2016 | 09:21 AM
#1
Thread Starter
Banned
Joined: Sep 2015
Posts: 85
Likes: 0
Using map coordinates
Anyone know how to use them by manual calculation?
You are at airport A located at 33’20”N 108’02”W and are flying to airport B located at 35’55”N 107’58”W. Approximately how many miles is it from airport A to airport B?
Thanks!
You are at airport A located at 33’20”N 108’02”W and are flying to airport B located at 35’55”N 107’58”W. Approximately how many miles is it from airport A to airport B?
Thanks!
02-08-2016 | 10:46 AM
#2
Line Holder
Joined: Jan 2016
Posts: 422
Likes: 0
Use the following (and if you can do it in your head, you're awesome):
Dlon = longitude2 - longitude1
Dlat = lattitude2 - lattitude1
a = (sin(Dlattitude/2))^2 + cos(lattitude1) * cos(lattitude2) * (sin(Dlongitude/2))^2
c = 2 * atan2( sqrt(a), sqrt(1-a) )
d = R * c (where R is the radius of the Earth in appropriate units - result will be same units)
This is from code, so where you see '*' think "multiplied by" or "times".
Dlon = longitude2 - longitude1
Dlat = lattitude2 - lattitude1
a = (sin(Dlattitude/2))^2 + cos(lattitude1) * cos(lattitude2) * (sin(Dlongitude/2))^2
c = 2 * atan2( sqrt(a), sqrt(1-a) )
d = R * c (where R is the radius of the Earth in appropriate units - result will be same units)
This is from code, so where you see '*' think "multiplied by" or "times".
02-08-2016 | 05:56 PM
#3
Gets Weekends Off
Joined: May 2010
Posts: 5,244
Likes: 2
From: Baja Vermont
N35*55' minus N33*20' equals 155nm of north-south distance. The two airports are separated by 4' of longitude, which at 34* of latitude is 3.31 nm, (cosines of 34). So, very slightly more than 155nm
Hint: one minute of latitude equals one nautical mile
GF
Hint: one minute of latitude equals one nautical mile
GF
02-09-2016 | 03:34 AM
#4
Gets Weekends Off
Joined: Jul 2007
Posts: 4,065
Likes: 40
From: 767 Captain
The two answers above remind me of the old bull and young bull joke. They're standing at the top of the hill looking down at the herd of cows. Young one says hey look at all those cows! Let's run down the hill and 
one of them. Old bull says, why don't we walk down and them all.
GF takes the wise, simple approach and could definitely get the answer in his head if desired.
Whoever posed this question was definitely looking for you to figure out it was essentially a northerly course from A to B and have you get the difference on the latitude minutes which equates to NM.
one of them. Old bull says, why don't we walk down and them all.GF takes the wise, simple approach and could definitely get the answer in his head if desired.
Whoever posed this question was definitely looking for you to figure out it was essentially a northerly course from A to B and have you get the difference on the latitude minutes which equates to NM.
02-09-2016 | 04:47 AM
#5
Line Holder
Joined: Jan 2016
Posts: 422
Likes: 0
So long as the two points are roughly N/S of each other, then the simple rule of one nm per minute of latitude totally works. But that's the only time it works, so it's an optimization of a specific case rather than a general solution to the question "Using map coordinates - Anyone know how to use them by manual calculation?" as the OP asked.
Personally, I favor the finger/thumb method - you know, finger on one coordinate and thumb on the other one in an EFB app which then tells you the bearing and distance. But the OP asked for the manual calculation :-)
Personally, I favor the finger/thumb method - you know, finger on one coordinate and thumb on the other one in an EFB app which then tells you the bearing and distance. But the OP asked for the manual calculation :-)
02-09-2016 | 02:45 PM
#6
Gets Weekends Off
Joined: May 2010
Posts: 5,244
Likes: 2
From: Baja Vermont
I think the point of the question was recognizing the fact it was a north-south problem and did the person see that and apply a basic bit of navigation knowledge. You could do the n-s part, apply the cosine of the latitude to the number of minutes from the E-W distance and scale it out on an HSI, but really?
GF
GF
02-09-2016 | 04:34 PM
#7
Gets Weekends Off
Joined: Jul 2007
Posts: 4,065
Likes: 40
From: 767 Captain
So long as the two points are roughly N/S of each other, then the simple rule of one nm per minute of latitude totally works. But that's the only time it works, so it's an optimization of a specific case rather than a general solution to the question "Using map coordinates - Anyone know how to use them by manual calculation?" as the OP asked.
Personally, I favor the finger/thumb method - you know, finger on one coordinate and thumb on the other one in an EFB app which then tells you the bearing and distance. But the OP asked for the manual calculation :-)
Personally, I favor the finger/thumb method - you know, finger on one coordinate and thumb on the other one in an EFB app which then tells you the bearing and distance. But the OP asked for the manual calculation :-)
02-09-2016 | 05:37 PM
#8
Line Holder
Joined: Jan 2016
Posts: 422
Likes: 0
As GF just said, the question targeted a specific aspect of Lat/Long knowledge. It wasn't designed to get someone to develop a multi-level trigonometry method that applies to any two sets of coordinates. If you really think the answer you provided was the best option for answering the question, then you probably haven't taken enough FAA tests.
02-09-2016 | 06:19 PM
#9
Gets Weekends Off
Joined: Jul 2014
Posts: 269
Likes: 0
As GF just said, the question targeted a specific aspect of Lat/Long knowledge. It wasn't designed to get someone to develop a multi-level trigonometry method that applies to any two sets of coordinates. If you really think the answer you provided was the best option for answering the question, then you probably haven't taken enough FAA tests.
Map= Obtained at AAA or DMA, (and used for Land Navigation).
Chart= Used for Aeronautical or Nautical Navigation, (and each use different projections).
My first FI would of slapped me if I ever asked him for a map.
I do admit I couldn't solve that equation without using artificial assistance.
Carry on
Last edited by NotPart91; 02-09-2016 at 06:30 PM.
02-10-2016 | 12:37 AM
#10
Gets Weekends Off
Joined: Jul 2007
Posts: 4,065
Likes: 40
From: 767 Captain
I must have slept through the FAA exams that referenced a "Map."
Map= Obtained at AAA or DMA, (and used for Land Navigation).
Chart= Used for Aeronautical or Nautical Navigation, (and each use different projections).
My first FI would of slapped me if I ever asked him for a map.
I do admit I couldn't solve that equation without using artificial assistance.
Carry on
Map= Obtained at AAA or DMA, (and used for Land Navigation).
Chart= Used for Aeronautical or Nautical Navigation, (and each use different projections).
My first FI would of slapped me if I ever asked him for a map.
I do admit I couldn't solve that equation without using artificial assistance.
Carry on
Not quite sure why I appear to be the target of your vocabulary lesson. The "M" word was used by the OP and I'm sure originated with him and not the test or textbook he referenced. Considering the question he posed and the way he did it, I felt the terminology error was beyond the scope of the situation.
Thread
Thread Starter
Forum
Replies
Last Post
