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Discussion Starter · #1 ·
Chaps who use their boats and gps regularly.

Whilst inputting a load of wreck marks etc I just wanted to checkt that Ive done one thing correctly - if the mark is 02 ... ... when I come to enter this on my gps it has three possible digits for the first bit so Ive been entering 002 - and not 020 - would that be correct because surely 02 is the same as 002 and not the latter 020 which is in effect 20 ?

Cheers
 

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If you're talking about the figures after the decimal point (otherwise you'll be well away from the UK entering 020) .020 is in fact the same as .02

On the other hand if you're talking about degrees and not fractions of a minute of (and talking about 2 degrees west for instance), then yes, 002 is the same as 02 - it will (should) be expressed as three figures as longitude can go to 180 degrees, whereas latitude can of course only go to 90 degrees hence it's expressed with just 2 digits.
 
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To save me typing it all again from the top of the head…………I am going to cut n paste from various sources with other info added in for good measure………

The datum that your data comes from is very important otherwise you could find yourself up to half a mile from where you think you are ………… generally most system today are based on WGS84 (World Geodetic System 1984 – revised in 2004)

WGS84 will need to be reviewed this year !

The other system we encounter in the UK is OSGB36 (Ordnance Survey National Grid reference system 1936), but this will be mainly land based and rarely used on marine charts.

Data formats entered into your GPS can be one of three, but you can set it up to do any of the three on the setup screens………

Degrees, Minutes, Seconds
Degrees, decimal minutes
Decimal degrees.

Remember ……….Zero degrees is a datum line so, -3W(est) is exactly the same as 3E(ast)………….


Here are the things to remember

There is no such thing as an “absolute” location reference, even latitude/longitude. Any given position reference (in latitude and longitude, British national grid or any other format) is valid only in terms of the particular map datum in which it was calculated.

Using the wrong map datum to find a position reference can result in errors up to half a mile.

You can switch between position formats without danger – they are simply different ways of formatting the description of a single point on the earth’s surface and do not affect the internal GPS record of the position.


Often, position references entered in one map datum will be displayed differently if you reset your GPS to another map datum. The displayed figures will, however, still be correct in the context of the new datum – so if you "goto" the point you will still get to the right place.

Setting a route based on waypoints collected in different map datums is fine, so long as the waypoints themselves were entered into the GPS in the correct individual datum’s, but you can get yourself into all sorts of trouble doing this.

If any data are manually entered, whether on GPS or computer, or written down, or given over the phone, or read off the GPS screen and told to someone else, then the correct datum must also be used or given or errors will result.


In an emergency, the Coastguard and other ships will always assume the position is relative to WGS84………….. 99% of today’s GPS units will assume WGS84 as the datum.

This link defines WGS84 …… http://home.online.no/~sigurdhu/WGS84_Eng.html

This link details the mathematical conversions….. http://home.online.no/~sigurdhu/Deg_formats.htm

If anybody wants more help then pm me ……….. but bear in mind I am busy and may take a while to respond.
 

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Discussion Starter · #6 ·
Blimey thanks for all the info ! To clarify this is the data to be entered -

50 18 47N 02 59. 73W 50 14 02N 003 02 635W

I would enter this on our GPS as follows :

50 18 047N 002 59. 073W 50 14 002N 003 02 635W

Would that be correct ?
 

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No - you're correct until the digital point - anything after the digital point, add the third digit as a 0 at the end

so 02 59.73W is 002 59.730W

02 is the same as 002, but .02 is the same as .020
 

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Blimey thanks for all the info ! To clarify this is the data to be entered -

50 18 47N 02 59. 73W 50 14 02N 003 02 635W
As you've got numbers exceeding 60'', the co-ordinates you want to enter seem to be in degrees, minutes, decimal minutes format (d)dd* mm.mmm . Make sure your GPS is set up to the same format.

You should enter:

050* 18.470 N 002* 59.730 W

and

050* 14.020 N 003* 02.635 W

Don't worry if you can't enter the first zero, as your set may only accept two digits for degrees of latitude. There's no point in three digits, because latitude can't practically exceed 90*, but some sets seem to be set up for three digits. If that's the case, the highest number you could put in would be 090* 00.000 N. (or S if you were in the antarctic).

Pennog.
 
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