Coordinate System

[StuM]

Originally Posted by Alan Mighty

Given that the Australian continent (and likely New Guinea too) is moving at 7 cm a year

Only in parts

Because PNG sits on the boundary between the Australian and Pacific plates, you are getting closer to us - so watch out!.

[patprice]

Thanks Geoffkimblin for...


Extract from Rod's Greek Pilot:-

"All waypoints are given in the notation:

degrees minutes decimal place of a minute

It is important not to confuse the decimal place of a minute with the older 60 second notation."

Then why put the ' (minutes sign) before the decimal part ? Confuses me but that might be easily done lol.

[patprice]

Yu savi tru lol!

[Sandero]

You can use asci code on a PC to write degrees


it is alt0176.... hold the alt key and type 0176 you get °

56alt179 prints 56°

for diameter

alt0216 writes Ø

12"alt0216 12"Ø

[deblen]

I was taught that there are two conventional ways to denote marine chart positions.

1. The somewhat outdated Deg Min Sec as in N44° 40 (min.) 30 (sec)

written as N44 40 30 with NO decimals

and pronounced as North forty four degrees forty minutes thirty seconds.
This defines a position within 60ft

2. Due to earlier digital eqpt limitations-(they couldn't compute seconds at first)
The modern system of Deg Min Dec. of a Min) as in N44° 40(min) .50

written as N44 40.50

and pronounced as North forty four forty decimal fifty
This defines a position within 60ft.

If you wish to bother with the 3rd digit in your GPS display of . sec or .01min (both 6ft) then I guess it would be OK to add a dot (decimal pt.) after the 2 digit seconds in example 1. above as:

N44° 40 30.5 & pronounced as
North forty four degrees forty minutes thirty decimal five seconds
though I can't think of a good reason why you would want to.
In the days when degrees minutes seconds were commonly used,no mariner was able to get down to 6ft.

With the advent of DGPS/WASS, 6 ft became possible-& decimals of a minute replaced seconds. as in :

N44°40.505
pronounced North forty four forty decimal five oh five.


When working with old charts that are marked in degree min. second format,it is advisable to be able to convert seconds to decimals of a minute for communication purposes.

It's very easy:

60sec = 1 minute
30sec = half a minute = .50 min.
15sec= qtr of min. = .25 min
Just divide the actual seconds by 60

This is my understanding for marine navigation use.

/ Len

[El Pinguino]

Originally Posted by deblen

I was taught that there are two conventional ways to denote marine chart positions....

2. Due to earlier digital eqpt limitations-(they couldn't compute seconds at first)
The modern system of Deg Min Dec. of a Min) as in N44° 40(min) .50

written as N44 40.50
........

This is my understanding for marine navigation use.

/ Len

The use of decimal minutes long predates the use of computers in daily sight reduction and general navigation..... although the first decimal place is all that was/is used..

At least 60 years and possibly more than 100 years since 'seconds' went west ( unless you are a french cartographer )..

Lecky, in his 'Wrinkles' - which dates back to the late 1800's - uses seconds in theoretical explanations but resorts to fractions of a minute ( to the nearest quarter ) in practical calculations....

'Right Ascension' outlived 'seconds' by many many years...

[deblen]

Originally Posted by El Pinguino

The use of decimal minutes long predates the use of computers in daily sight reduction and general navigation..... although the first decimal place is all that was/is used..

At least 60 years and possibly more than 100 years since 'seconds' went west ( unless you are a french cartographer )..

Lecky, in his 'Wrinkles' - which dates back to the late 1800's - uses seconds in theoretical explanations but resorts to fractions of a minute ( to the nearest quarter ) in practical calculations....

'Right Ascension' outlived 'seconds' by many many years...

Thanks for the history.
I had to Google "Right Ascension"

Guess I'll leave RA to astronauts

I'm happy to know where I am on currently available nautical charts using currently common nav aids-no sextant-mostly GPS,pencil & parallel rule (or a handy straight edge)
Cheers/ Len

[El Pinguino]

I should have said ...'Right Ascension' outlived 'seconds' by many many years... in practical navigation.

Up until... I think about WW2... before my time anywaze... when they stopped listing it in the Nautical Almanac.

It was replaced by SHA or sidereal hour angle... which are measured west about rather than east about so life was made simpler as both GHA Aries and the SHA of a star were always additive and if you were in the eastern hemisphere it was additive as well.

Also I think I am correct in saying that while SHA, and also LHA and GHA are expressed in degrees RA was expressed in 'hours'....

[El Pinguino]

This will be enough to give you a brain bleed....

I've just dug out a bit of info from an 1880 almanac reproduced in the back of my copy of 'Lecky's Wrinkles'

Right Ascension is listed in Hours, Minutes, and Seconds ( to two decimal places) ... that's time.. not arc.... while declination is listed in D.M.S of arc...

There is a conversion table to take you from H.M.S to D.M.S......... thats nice..

Nothing like keeping things simple ....

[StuM]

Originally Posted by Sandero

You can use asci code on a PC to write degrees


it is alt0176.... hold the alt key and type 0176 you get °

56alt179 prints 56°

for diameter

alt0216 writes Ø

12"alt0216 12"Ø

Just to be pedantic

That's not "asci" [sic] code (ASCII). ASCII is a 7 bit character set. (Codes 0 - 127)

It is actually ISO 8859-1 Extended ASCII (aka ISO Latin-1). One of many encodings for the codes 128-255. It is the default encoding in Windows for Western European languages, which is why it works for most of us.
(More accurately, Windows uses a superset of ISO 8859-1 called "Code Page Windows-1252"


(BTW, you may have missed Post #6 )

[deblen]

You two are making me jealous that you have so much spare time.
Can you sand & apply varnish as well??

[StuM]

Originally Posted by deblen

If you wish to bother with the 3rd digit in your GPS display of . sec or .01min (both 6ft)

1/10th of a second and 1/100th of a minute can't both be 6ft

0.1 seconds is about 10ft.
0.01 minutes is about 60ft.
(0.001 minutes is about 6 ft)

[StuM]

Originally Posted by El Pinguino

This will be enough to give you a brain bleed....

I've just dug out a bit of info from an 1880 almanac reproduced in the back of my copy of 'Lecky's Wrinkles'

Right Ascension is listed in Hours, Minutes, and Seconds ( to two decimal places) ... that's time.. not arc.... while declination is listed in D.M.S of arc...

There is a conversion table to take you from H.M.S to D.M.S......... thats nice..

Nothing like keeping things simple ....

If you can multiply and divide by 15, you don't need no steenking tables

[StuM]

Originally Posted by deblen

You two are making me jealous that you have so much spare time.
Can you sand & apply varnish as well??

Who needs to sand and varnish when you sail two chlorox bottles tied together

[deblen]

[QUOTE=StuM;2176732]1/10th of a second and 1/100th of a minute can't both be 6ft

0.1 seconds is about 10ft.
0.01 minutes is about 60ft.
(0.001 minutes is about 6 ft)[/QUOTE

You are picky-but correct.
1 nm = somewhere around 6080ft=1 min. of Lat......etc.

I should have used .001 min. = 6ft

BUT!! I speak of PRACTICAL vessel navigation & I maintain that the avg. user will never work with 6 or 10 ft.
Besides-derived position is the antenna location-so IMHO-for practical purposes,going beyond two decimal points on a GPS display was a big marketing ploy & adds only confusion to the avg user.

I find it hilarious when a boater reads his position over the air to 3 decimals.

OK-back to varnishing Have a nice day! Find something useful to do.