Any advantage of the DMS system over the Decimal Degree?

Forgot to add - from the CAA data:-

1 ARP co-ordinates and site at Aerodrome: Lat: 555700N Long: 0032221W Centre of
Runway 06/24.
2 Direction and distance from the city: 5 nm W of Edinburgh.
3 Elevation/Reference temperature: 136 ft – 19°C.
4 Geoid undulation at AD ELEV PSN: 173 ft.
5 MAG VAR/Annual change: W3.7° (2010) – 0.17° decreasing.


I reckon the web site error is at least 20 NM.

 

That's quite the large airport. 0.3 degrees of latitude is over 20
miles and even if you're talking about longitude at 60 deg. N it would
still be over 10 miles.

 

I suspect you used a calculator :-(

At the equator 1 degree of longitude is around 69 miles and at 60 degrees it
would be half that, say 35 miles. So 2 miles at that same latitude would be
around 0.06 of a degree or around 3 1/2 minutes.

 

actually 0.3 deg latitude is 0.3 nautical mile. 0.3 deg longitude at
60deg north or south is near enough to 0.26 nautical mile

 

oops .. correct, I used degrees instead of minutes

at 60 deg latitude, 0.3 deg = sin (latitude) * (.3*60) = 15.6 Nautical
miles

 

Not at all.

The above would be true (or close enough) if you replaced "deg" by
"min".

 

As you can tell, I didn't read this post before I replied to the other
one.

indeed...

Sorry.

 

NP

teach me to check what I typed before hitting send button

 

Now why do I think that problme isn't unique to you?

[I left the errors in just to whow why I have to do it too.]

[But do I always rmember? I leave that as an exercise for th reader.}

 

You are replying to a message that is almost 3 years old. It is
still a relevant topic though.

I personally like the pure decimal notation for the sake of its
mathematical simplicity, but there is a good reason to use
degrees, minutes, and decimal minutes instead, because that is
what most GPS maps use. It is something like a standard. It is
also the default setting on Garmin GPS receivers, I believe.

One reason why maps use it is that along the meridians and along
the equator each minute is a nautical mile. So, for example,
S 1° 16.35' is 60 + 16.35 nm = 76.35 nm south of the equator.

If I had to report an emergency and its GPS coordinates over the
phone, I would use this notation first and stick to it until the
phone operator tells me otherwise, thus: "south one degree, 16
decimal 3 minutes."

Hans-Georg

 

DD.MM.mmm

I have not seen a nautical chart or aeronautical chart with other than DD.MM.mmm for many many years, especially since charts went metric, all the lat/long show minutes divided in tenths. (1M = 1NM = 1852metres).

However it is all academic really as long as the source and destination are both expressed the same way then no problem.

Depending on the age of what you are looking for pre 1984/94 and post that era can cause confusion with the Datum. There are well over 100 to chose from mostly effecting Grid maps based on UTM.

As for UTM, a great system for short (less than 6 degrees/360nml ) navigation on land but with 60 separate datum reference points it is critical you get the right one as it is a "local" system not an international one and only 30% of the globes surface is land.

The key difference is that UTM ALWAYS runs East (X) then North (Y) from the nearest (false) datum point.
vs
Lat/Long that runs east or west (-) then north or south (-) from the datum point of 0 deg lat and 0 deg long. WSG84 defines where this is as at 1984. This can confuse when you look at the square you have defined as to whether you have defined the left or right/top or bottom corner.

Here in Australia the most pre 1994 Grid maps are called AGM and the Post 94 GMA so if you are using recent maps then GMA is the one and it is directly compatible with WSG84 that the satellites GPS default too.

All in all a fascinating subject that goes on and on, I presented a 4 page paper on coordinate conversion in an attempt to simplify and clarify the issue as I have seen so many confused/arguing with what it should be and getting lost.

Kevin Hutch.
@hotmail.com