Longitude & Latitude advice

[sfakman]

I'm currently revising for my nav exam.

From searching threads around here it appears to be a key requirement to have an excellent understanding of longitude & latitude co-ordinates.

I'm just using the example in the PPL confuser which has N5050.03 E00017.57 for Shoreham. I get the N5050.03 bit and I understand the principle of Degrees, Minutes, Seconds but for the co-ordinates E00017.57 - I'm getting confused. I'm using the Air Pilots Manual (the green book) but it doesn't appear to go into much detail - unless I've missed it?

I’ve scoured the Internet for a better explanation but I’m struggling. I know it’s a fairly simple issue – I just need someone to explain it to me (ideally, using the Shoreham example so I can picture it in my mind).

Thanks!

[trident3A]

Degrees latitude goes from 0-90 but longitude is from 0-180, so longitude has an extra digit - is that what's confusing things?

(edited to make sense)

[Mariner9]

Trident meant the extra digit is in the longitude.

Therefore E00017.57 is East 000 degrees, 17 minutes, and (just to add a further complication) either 57 seconds or 0.57 (decimal) of a minute, depending on the format used :rolleyes:

Edited to add that in reality, Shoreham (the airfield that is) is actually in the western hemisphere (N5050.13 W00017.83 according to the AFE guide :ugh:)

[asyncio]

Edited to add that in reality, Shoreham (the airfield that is) is actually in the western hemisphere (N5050.13 W00017.83 according to the AFE guide :ugh:) There was a thread about this in Flyer, it looks like there are lots of errors in the current edition

PPL Confuser 9th Ed - Full of errors (http://forums.flyer.co.uk/viewtopic.php?f=5&t=56471&start=0)

[HEATHROW DIRECTOR]

<<Longitude & Latitude advice>>

sfakman.. Just to confuse you further, by convention co-ords are usually given in the form Latitude and Longitude rather than as given in the thread title. I think one reason there is confusion is that various publications convert co-ords for use in GPS and other nav systems. The old fashioned "degrees, minutes, seconds" was pretty foolproof.

Good luck with the nav exam..

[BackPacker]

There is indeed a lot of confusion about the notation. There are three possibilities:

degrees, minutes, seconds
degrees, minutes, decimal fractions of minutes
degrees, decimal fractions of degrees.

What you see regularly is that the symbols for degrees, minutes and seconds are left out but this has no consequence: we're still talking degrees, minutes and seconds. But as soon as a decimal point (.) is introduced, everything behind it is the decimal fraction of whatever came before. And the decimal point is never omitted.

So...

N505013 would be 50 degrees, 50 minutes and 13 seconds north.
N5050.13 would be 50 degrees and 50.13 minutes north (= 50 degrees, 50 minutes, 7.8 seconds)
N50.5013 would be 50.5013 degrees north (= 50 degrees, 30 minutes, 4.68 seconds)

And as others have said, for longitude the degrees can range up to 180 degrees, so degrees of longitude are always three digits.

[Keygrip]

I was of the impression that any number that started with 00 (including Latitudes) added an extra 0 - to make it 000.

[BackPacker]

I was of the impression that any number that started with 00 (including Latitudes) added an extra 0 - to make it 000.
Well, I've never been that close to the equator for that to be an issue and I also don't have any official flight guides or anything for that region here.

However, the Pilots Free Flight Atlas (one of those "must have" gimmicks) does nothing special in the notation for Supadio (WIOO/PNK) in Indonesia (S000852 E1092414), nor for Temindung (WALS/SRI; S002855 E1170924).

[prettygrumman]

I thought I understood it all- now im totally confused:rolleyes::rolleyes:

[sfakman]

Thanks everyone - I had issue 8 of the PPL Confuser but due to over-use, it fell apart so I bought another one which was issue 9. And yes, there are a lot of errors - the most annoying being the fact it highlights the answers in bold on a whole bunch of the questions. Very annoying.

Anyhow, I think this is beginning to sink in now.

So, to summarise:

There are 3 digits for Longitude so that will explain the "000" in E00017.57. This makes sense.
The PPL Confuser is wrong and the Longitude should actually be W00017.83.
In this example, because Shoreham is between East & West, it is at 000. As Mariner9 pointed out, Shoreham is in the Western hemisphere which will explain why it is to the West (or left) off the 000 mark.
The decimal point can appear after degrees, minutes or seconds. If the decimal point was to appear after the first two digits (degrees), then the digits after the decimal point are relevant to degrees. This same approach can be used after minutes and seconds as well. If the decimal point appears after degrees you wouldn’t then have a figure for minutes or seconds. If the decimal point appeared after minutes, you would have any figures for seconds.
As Shoreham is 17.83 minutes West I simply count 17 of the dashes to the left and .83 is just a finer, more accurate position between the 17 and 18 marker. I think the penny has dropped. Unless any of the above is wrong?

Thank you VERY much for this - I really appreciate it.

[BackPacker]

As Shoreham is 17.83 minutes West I simply count 17 of the dashes to the left and .83 is just a finer, more accurate position between the 17 and 18 marker.

17.83 minutes = 17 minutes and 60 * .83 = 49.8 seconds. But you knew that, right?

Anyway, by definition one minute of latitude (note: NOT longitude) is 1 nm so if you only get the degrees and minutes right you can't be more than a nm off.

[LH2]

Anyway, by definition one minute of latitude (note: NOT longitude) is 1 nm

Well, just to be pedantic, by definition one nautical mile equals exactly 1852m and has been the case in most areas of the world since some time before WWII. That is of course around the time when they last revised the PPL/CPL curriculum, so the confusion is understandable :}

"One minute of latitude" by itself can mean dozens of different things even in a fairly well defined context, so it was a good enough measure of distance back when travel times were measured to the nearest day, not to the minute or less as is the case nowadays.

[BackPacker]

I knew there would be one... :ok:

Nautical mile - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Nautical_mile)

[liam548]

I'm currently revising for my nav exam.

From searching threads around here it appears to be a key requirement to have an excellent understanding of longitude & latitude co-ordinates.

I'm just using the example in the PPL confuser which has N5050.03 E00017.57 for Shoreham. I get the N5050.03 bit and I understand the principle of Degrees, Minutes, Seconds but for the co-ordinates E00017.57 - I'm getting confused. I'm using the Air Pilots Manual (the green book) but it doesn't appear to go into much detail - unless I've missed it?

I’ve scoured the Internet for a better explanation but I’m struggling. I know it’s a fairly simple issue – I just need someone to explain it to me (ideally, using the Shoreham example so I can picture it in my mind).

Thanks!


this has been asked many times. I asked it then a few weeks after someone else came across the same isues with shoreham and confuser. See my thread:)

http://www.pprune.org/private-flying/365910-coordiantes-shoreham.html

[Sultan Ismail]

Just to add to the confusion and as an addendum to Backpackers' comment I attach an extract from a Singapore NOTAM. Singapore is One degree above the Equator and 104 Degree East of Greenwich. You can work out the rest yourself.

A1043/09 - ONE RIG, HGT 150M AMSL, BERTHED AT 0126.48N 10400.35E (BEARING 011 DEGREES, DISTANCE 9264M FROM WSSS ARP). RIG MARKED AND LIGHTED. 03 JUL 00:41 2009 UNTIL 30 SEP 23:59 2009. CREATED: 03 JUL 00:58 2009

[Whopity]

Until we had Inertial Navigation nobody bothered about anything less than 1 minute of arc (1nm) unless you were dropping bombs, then the next level was to seconds. Then came GPS and computers and programmers who decided that decimal degrees and minutes were more appropriate that the conventional units and confused everybody.

For most of Shoreham's long history it was N5050 E00017 and that's good enough for me.

[Crash one]

For most of Shoreham's long history it was N5050 E00017 and that's good enough for me.

It says 17mins West on the SE chart which looks like about 22 miles away from 17min East??

[Gertrude the Wombat]

programmers who decided that decimal degrees and minutes were more appropriate that the conventional units and confused everybody
Unlikely. The programmers will code whatever they're told to, all these representations are as easy as each other (yes, I have done it myself). I think you're looking at the product design people, not the programmers.

Of course I suppose that in a completely crap company with no management and no quality system and no clue what they're doing other than they're "making cool widgets" the poor sod of a programmer might be stuck with making decisions like this without sufficient input from users - not all programmers are old and experienced enough to spot what's wrong with a place like that and find another job.

[Jofm5]

Yes gertrude - Us programmers are just automated machines that do the biddings of others without questions........

You may work that way - but in my 20 years I never have - if I dont understand the fundamentals I refuse to work on it.

I think you will find there are no "programmers" but there are "analyst programmers" if you want to put labels on things - we professionals tend to understand what we are writing rather than just write to a specificaiton - I would rather you did not denigrate the whole of our industry with your assertions.

[Whopity]

It says 17mins West on the SE chart which looks like about 22 miles away from 17min East??Sorry, Just cut and pasted it from the original post!

Lets say before we had computers we didn't use decimal degrees! how they got there is immaterial except that it was clearly easier to do than work to another level based on seconds. Either way, the average GA pilot does not need the extra level of accuracy it gives!

[Crash one]

Lets say before we had computers we didn't use decimal degrees! how they got there is immaterial except that it was clearly easier to do than work to another level based on seconds. Either way, the average GA pilot does not need the extra level of accuracy it gives!

I'd go along with that.
What surprises me is that the computerisers, when they went to decimal degrees, didn't go all the way. 100 degrees in a right angle, divided into decimals after that, simple.
As an aside, in the engineering business, CNC machine tools move in X, Y or Z. Circles are programmed from C zero which is to the right (east to us) as you stand facing the machine, then anti-clockwise thru 360 deg. Therefore 090deg on a CNC mill is North to my way of thinking 180=West etc. I often wondered what kind of bird brain thought that up!
I have also worked in "Ams"? decimal parts of an hour, 6 mins, in time & motion planning!!
These things would be fine if just one system was universal, whichever system, but not a combination of umpteen.

[Gertrude the Wombat]

Yes gertrude - Us programmers are just automated machines that do the biddings of others without questions........

You may work that way - but in my 20 years I never have - if I dont understand the fundamentals I refuse to work on it.

I think you will find there are no "programmers" but there are "analyst programmers" if you want to put labels on things - we professionals tend to understand what we are writing rather than just write to a specificaiton - I would rather you did not denigrate the whole of our industry with your assertions.
What a silly boy.

I've only being doing the job for several decades - given such a job I would not, as you suggest, and as Whopity originally suggested, make up the representation for myself, I would manage to spot that this was a sufficiently important feature that people other than the programmer should be involved in specifying it, and if it wasn't in the spec I'd nag people until it was.