Degrees, Minutes, Seconds vs Decimal Degrees

[Martkimwat]

Originally Posted by SeanPatrick

I've done calculations with degrees and decimal minutes for so long that I can convert to decimal degrees and back in my head. It's easy to do:


Let's say you want to convert say 37.3 minutes to decimal form. 6 · 6 = 36, and 6 · 7 = 42, so we know we'll start with 0.6°. The remainder is 1.3'. 6 · 2 = 12, so 6 · 0.2 = 1.2. Now we have 0.62° and the remainder is 0.1'. 6 · 2 = 12, so 6 · 0.02 = 0.12. 0.622° = 37'19.2" or 37.32'. Close enough.


Of course, you could keep going ...



But I prefer to use degrees and decimal minutes.

I think you meant 'FROM decimal format TO degrees and minutes...' 37.3 minutes is already in decimal format but having said that, the rest of your calculations don't make sense either because 0.3 is 30% of 60 seconds = 18", so the correct answer would be 37'18". your calculations have gone full circle to arrive back at 37.32 decimal minutes although you have arrived at two decimal places which you are now incorrectly calling seconds. Take it from a senior commercial aviator of forty plus years experience, you've got it wrong, either in you calculations, your terminology or both.

[flightlead404]

Originally Posted by Orin

Nobody cares that we had a perfectly well thought out system that had survived thousands of years of refinement when they suggested that we divide a longitudinal line up into 2 million pieces and call one a meter just to make everything base 10... cuz heck whoever came up with this base 6,12,24,60 system.... whatever it is

Bloody Babylonians again lol

[requiem]

Originally Posted by Martkimwat

I think you meant 'FROM decimal format TO degrees and minutes...'

I could follow it, he's just going from decimal minutes (37.3') to decimal degrees (0.xxx°). It becomes much more obvious once you realize he's simply doing long division in his head with 6 instead of 60, and sliding the decimal back at the end.

 
    0.6216...
6 ) 3.73

[StuM]

Originally Posted by Martkimwat

I think you meant 'FROM decimal format TO degrees and minutes...' 37.3 minutes is already in decimal format but having said that, the rest of your calculations don't make sense either because 0.3 is 30% of 60 seconds = 18", so the correct answer would be 37'18". your calculations have gone full circle to arrive back at 37.32 decimal minutes although you have arrived at two decimal places which you are now incorrectly calling seconds. Take it from a senior commercial aviator of forty plus years experience, you've got it wrong, either in you calculations, your terminology or both.

He didn't get it wrong, you apparently misunderstood

(Why is it that when posters feel the need to expound on their many years of experience, they are so often themselves wrong? )

He was actually converting decimal minutes to decimal degrees i.e. 37.32' to 0.622°
He then converted back again to decimal minutes. i.e. 0.622° = 37'19.2" or 37.32

Since his initial calculation was only an approximation (it's actually 0.6216666...), his reverse calcuation came up with a slightly different value to his start figure.
0.61666666...° = 37.3' = 37'18"
0.62 = 37.32' = 37'19.2"

[Martkimwat]

Originally Posted by requiem

I could follow it, he's just going from decimal minutes (37.3') to decimal degrees (0.xxx°). It becomes much more obvious once you realize he's simply doing long division in his head with 6 instead of 60, and sliding the decimal back at the end.

 
    0.6216...
6 ) 3.73

Then as I said, his terminology is wrong, ie ambiguous, he should have stated
"to change 37.3 decimal minutes to decimal degrees". I thought he was trying to explain how to convert decimal minutes into minutes and seconds, is why I could not make sense of it. Also might have helped in the example, to use another unit of numbers that did not coincidently end up so close to the same numbers in the subsequent calculated answer. I didn't bother to follow the reasoning because just comparing the answer with the original figure, it was obviously not correct as far as minutes and seconds were concerned ( which I did in my head as well) and the answer looked almost identical to the original figure. First rule when giving examples is not to make the calculation and explanation ambiguous. (as an aside, have never seen a full stop used to denote the multiplication sign, normally use x or *, where does that come from? again ambiguous because I thought he meant 6.6 as in 6 decimal point 6)

[Wotname]

Originally Posted by StuM

Degrees and decimal minutes:
Nine degrees two seven point nine minutes south, one four seven degrees nine point two minutes east.


Decimal degrees:
Nine point four six five degrees south, one four seven point one five three degrees east.

Interesting....

Has things changed in last 5+ decades.

I would always say


Nine degrees two seven decimal nine minutes south, one four seven degrees nine decimal two minutes east.

and

Nine decimal four six five degrees south, one four seven decimal one five three degrees east

Pronounced day-see-mal.

Not saying my way is correct, just saying that is how it was done. Is it done differently now?

[StuM]

Originally Posted by StuM

He was actually converting decimal minutes to decimal degrees i.e. 37.32' to 0.622°
He then converted back again to decimal minutes. i.e. 0.622° = 37'19.2" or 37.32

Oops, I stuck an extra "2" in there!

[capt jgw]

Originally Posted by sailorboy1

I like to use the units that my chartplotter likes

Any chart plotter will "like" whatever format you tell it to. It's just a matter of figuring out how to change the settings. They come defaulted to decimal minutes because that was is about the designed accuracy of the GPS system. Now days it can be as accurate as 10' on a good day, but originally it was around 100'. Around 300' when Selective Availability was active. Attempting to define a GPS position to a greater precision than GPS can deliver is pointless.

[StuM]

Originally Posted by Martkimwat

(as an aside, have never seen a full stop used to denote the multiplication sign, normally use x or *, where does that come from?

https://en.wikipedia.org/wiki/Multip...nd_terminology

• Multiplication is also denoted by dot signs,[3] usually a middle-position dot (rarely period):

5 ⋅ 2 or 5 . 3The middle dot notation, encoded in Unicode as U+22C5 ⋅ DOT OPERATOR, is standard in the United States and other countries where the period is used as a decimal point. When the dot operator character is not accessible, the interpunct (·) is used. In the United Kingdom and Ireland, the period/full stop is used for multiplication and the middle dot is used for the decimal point, although the use a period/full stop for decimal point is common. In other countries that use a comma as a decimal mark, either the period or a middle dot is used for multiplication

[StuM]

Originally Posted by Martkimwat

Then as I said, his terminology is wrong, ie ambiguous, he should have stated
"to change 37.3 decimal minutes to decimal degrees".

"I can convert to decimal degrees and back in my head. It's easy to do:" seems quite unambiguous to me. (And ambiguous <> wrong)

[El Pinguino]

Originally Posted by Wotname

Interesting....

Has things changed in last 5+ decades.

I would always say


Nine degrees two seven decimal nine minutes south, one four seven degrees nine decimal two minutes east.

and

Nine decimal four six five degrees south, one four seven decimal one five three degrees east

Pronounced day-see-mal.

Not saying my way is correct, just saying that is how it was done. Is it done differently now?

No.... correct usage is still 'decimal'

https://www.youtube.com/watch?v=NufAKh0ux8E

[StuM]

Originally Posted by Wotname

Interesting....

Has things changed in last 5+ decades.

I would always say

Nine degrees two seven decimal nine minutes south

I thinks it's a matter of choice.
I originally learnt the phoneitc alphabet in the military using the NATO system:

"In the NATO alphabet, punctuation marks are referred to by their name, with a few exceptions: a hyphen (-) is referred to as a dash, a period (.) is referred to as a stop, and a decimal point is referred to as a point or as a decimal."

[capt jgw]

Originally Posted by Rob_P

The hard part is adding or subtracting whiskey from true virgins. First, you have to find willing virgins. Then you need to convince them to make a beer run. Then you wait and hope they come back so you can find out where you are.

Currently, I'm going broke and getting dehydrated.

We always had fun with that one in the USCGAux navigation courses. Eventually the CG said we couldn't use the True Virgins rhyme anymore, so I'd start out by saying "I'm not allowed to teach it this way anymore, but this is how I learned it..." Then I'd teach it the same way I always had, using True Virgins. Never had a complaint.

[chrisr]

Originally Posted by capt jgw

We always had fun with that one in the USCGAux navigation courses. Eventually the CG said we couldn't use the True Virgins rhyme anymore, so I'd start out by saying "I'm not allowed to teach it this way anymore, but this is how I learned it..." Then I'd teach it the same way I always had, using True Virgins. Never had a complaint.

i have just - belatedly - worked out what rob_p was talking about (converting true to compass ?)

we, being young gentlemen officers, did not know about such things as whisky and virgins and were simply taught "error east, compass least. error west, compass best"

after a few floggings it stuck - but no doubt whiskey & virgins works too

cheers,

[El Pinguino]

True Virgins Make Dull Companions
=
True Variation Magnetic Deviation Compass

Sort of what one might call the 'order of work' or the order in which variation and deviation were applied.

error east compass least , error west compass best relates to which way to apply var and dev.