Help , LONG and LAT

[BAKERMAN]

Not 100% understanding LONG/LAT thingies

In books they are shorter than on GPS, I have been adding 00 on the end is that the wrigth thing to do.

Also trying to add on MAPSAUCE and failing due to my lack of knowlage.

 

[Clive]

Adding 00 on the end may work sometimes - it depends which "datum" is being used in the books. Have you got some examples ?

In Mapsource - if you go to Edit/Preferences/Position - you can change the datum used (WGS 84) is the usual one.

 

[Wraithwrider]

Steve

I'm not exactly sure what your problem is but I'll try to help.

Latitude & Longitude is written as Degrees and Minutes and decimal places of minutes.

Latitude (up & down) Starts at zero at the equator and goes up & down North or South 90 degrees max (the poles).

Longitude starts at Greenwich and goes 180 degrees East or West and meets at the 'back' of the planet so to speak!

So you have degrees, the next unit is minutes of which there are 60 i.e. 60 minutes in a degree. The next unit used in mapping isn't seconds but decimal points of a minute.

Interestingly one minute of Latitude = one nautical mile but only at that latitude.

So, on Mapsource the White Hart in Andover is:

N51 12.380 W1 28.835

That's thats same conventionally from books and maps as (I will use the word degrees instead of the 'little circle' symbol cause I don't know how to get it on my screen):

50degrees 12'.380N 1degree 28'.835W

You often don't see so many decimal points used from books and maps but you can just fill in the gaps with zeros.

Does that help?

Peter

 

[BAKERMAN]

Great reply Peter working my way through it cheers

In Chris Scotts Sahra book reads

N31* 07.0`W05* 10.1`

and I don`t seem to be able to transfur this into my MAPSAUCE.

 

[Wraithwrider]

That should be:

N31 07.000 W05 10.100

or maybe

N31 7.000 W5 10.100 perhaps

??

 

[Wraithwrider]

The first one worked. I've now got a waypoint called Andover in the middle of the Sahara Desert!!!

 

[Droopy Dick]

Latitude & Longitude is written as Degrees and Minutes and decimal places of minutes.

Ahem ....

not one to be awkward, but Lat/Long is writtenas :: degrees: minutes:seconds.

NOT decimal points. They are all base 60 numbers.

Incidentally, because the earth is not a perfect sphere, a nautical mile is not the same length in feet at a;ll points on the earth. A nautical mile is the length of arc subtended by one minute of latitude. This means that knots (nautical miles per hour) also vary in mph terms ...

Oh and for those doing long distance flights/voyages involving large north/south distances, it kinda makes the nav calculations just that little bit more interesting

 

[(RIP) Kaister]

so use a computer...... ???

 

[Wraithwrider]

Droopy

I do agree that historically speaking Lat and Long is expressed in Degrees, minutes & seconds.

BUT for the purposes of naviagation i.e. charts it is expressed in Degrees, minutes and decimal places of minutes.

BR1839 An Introduction to Coastal Navigation 'A Seaman's Guide' page 11.

Seconds ARE however used to express degrees of arc.

Peter

 

[Greg Masters]

Ahem ....

not one to be awkward, but Lat/Long is writtenas :: degrees: minutes:seconds.

NOT decimal points. They are all base 60 numbers.

Yes, this is a tricky one. Unfortunately, one of the Garmin standards is degrees then minutes then decimal point minutes - not seconds!

The writer and the reader both have to clearly understand which units are being used. One of the giveaways is if the 'decimal' figure exceeds 59 - then you know that it is decimal minutes, not seconds.

This doesn't help much in Bakerman's query, although, as it happens, determined both ways, the two possible locations are only 346 feet apart - both in the middle of nowhere about 59 miles SWW of Erfoud!

More lost with a GPS than without it!!



Greg

 

[Wraithwrider]

Greg

It's not really tricky.

The convention is to use decimal points.

Just grab any Admiralty chart or OS map and check it out.

Peter

 

[(RIP) willstatt]

It's all possible

Just been doing the same thing.... putting the Chris Scott routes into my GPS.

I'm not in front of my own PC at the mo, but from memory... there's a menu item that gives the option of the various formats to show the Lat Longs in.... and one is in the same Format as Chris Scott....
If you can't find it, I'll have a look and give you a bett explanation this evening.

Will

 

[BikerDave]

Adding 00 on the end may work sometimes - it depends which "datum" is being used in the books. Have you got some examples ?

In Mapsource - if you go to Edit/Preferences/Position - you can change the datum used (WGS 84) is the usual one.

The datum (eg WGS 84) is used to calculate/convert grid references to geodetic references - ie to Lat/Lon. It doesn't specify how it is displayed.

The default within MapSource for the display of Geodetic Grid References (selectable from Edit/Preferences/Position) is hddd:mm.mmm.

This translates as heading (N/S or E/W) degrees (3xdigits) and minutes (2xdigits + 3xdecimal points).

If you're given a Ref of N51:00/W1:23, this can be entered as N51:00.000/W001:23.000.

You can also select hddd:mm:ss.s (degrees/minutes/seconds to 1xdecimal place) as well as BNG (British National Grid), MGRS (US Military Grid Reference System) and a whole host of others, so you need to check which one you've selected.

 

[Taff]

Not 100% understanding LONG / LAT thingies. In books they are shorter than on GPS, I have been adding 00 on the end is that the wrigth thing to do. Also trying to add on MAPSAUCE and failing due to my lack of knowlage.

1. Give us an example of the Lat / Long you want to find or enter on the computer.

2. Are you happier using OS Grid Refs ?

 

[birdseye]

Ahem ....

not one to be awkward, but Lat/Long is writtenas :: degrees: minutes:seconds.

NOT decimal points. They are all base 60 numbers.

Incidentally, because the earth is not a perfect sphere, a nautical mile is not the same length in feet at a;ll points on the earth. A nautical mile is the length of arc subtended by one minute of latitude. This means that knots (nautical miles per hour) also vary in mph terms ...

Oh and for those doing long distance flights/voyages involving large north/south distances, it kinda makes the nav calculations just that little bit more interesting

Technically a nautical mile doesnt vary and is defined as 1852 metres - the sea mile which does vary a little (from 1843 to 1862 metres depending on latitude and horizontal datum) is the one that corresponds to one minute of arc. So the conversion from knots (nautical miles / hour) to statute miles per hour doesnt vary - not that a difference of 1% when going from the pole to the equator would figure high in my list of worries anyway. But interesting though all that is, I suspect its irrelevant to the problem described.

Nav data for GPS is expressed as degrees and minutes and decimals of a minute - no seconds. Latitude is expressed in 2 figures of a degree eg N58 but longitude is in three figures as in W002

As an example, my Garmin is showing N 52 33.158' W003 58.061' at the moment with a degree symbol in the space I've left. So it could simply be the format you are entering is wrong.

 

[Number 6]

I had the same problem with my Quest last week, not realising there were two ways of displaying co-ordinates I have set mine now to degrees, minutes and decimal points instead of degrees, minutes and seconds. Bakerman, have you tried altering the display settings? on the Quest it's done via Settings/Units setup/Location Format WGS 84 is used for both methods of displaying co-ordinates.

Birdseye, good info, thanks. (I hope you're in a boat )

 

[BAKERMAN]

1. Give us an example of the Lat / Long you want to find or enter on the computer.

2. Are you happier using OS Grid Refs ?

1. N31* 07.0`W05* 10.1

2. 35 Years ago yes

 

[(RIP) willstatt]

Hi Bakerman,

If you go to Edit/Preferences/Position on your PC in Mapsource, two boxes appear.

The lower one should show WGS 84 as the datum,

and the upper 'Grid' box should show

Lat/Lon hddd' mm.mmm which gives you the same format as the coords in Scott's book.

Worked for me anyway

Will

 

[(RIP) willstatt]

So in your example

just enter

N31 07.0 W05 10.1

in the position box of a 'new waypoint properties box'

Hope that works on your PC too

 

[BAKERMAN]

So in your example

just enter

N31 07.0 W05 10.1

in the position box of a 'new waypoint properties box'

Hope that works on your PC too

That did it, I was not going to the country, I was expecting the county to be instantly displayed