PDA

halo
10-12-2005, 15:38
hi all,not sure if this is the right place but could any of you extremely knowledgable folk explain longitude and latitude or where i might find a tutorial? :confused:

many many thanks

halo

merry christmas all

torjusg
10-12-2005, 15:47
Latitude can be measured by a sextant. Found these:

http://www.science-teachers.com/space/north_star/MeasuringLatitude.do

http://vesuvius.jsc.nasa.gov/er/seh/navigate.htm

Torjus Gaaren

Goose
10-12-2005, 23:26
How basic, or advanced do you need it to be?

Ogri the trog
10-12-2005, 23:36
hi all,not sure if this is the right place but could any of you extremely knowledgable folk explain longitude and latitude or where i might find a tutorial? :confused:

many many thanks

halo

merry christmas all

Longitude are the lines running from pole to pole like a chocolate orange.
Latitude are the ones that are like onion rings.
The theroretical grid that they produce on the surface of the globe means that by a system of angular measurment, any place can be pinpointed by dividing the angles into ever smaller divisions.

Simple init :confused:

Ogri the trog

Surveyor
11-12-2005, 01:50
Ogri,
Latitude is how far North or South you are, measured from the Equator.
This goes from 0 degrees at the Equator, to 90 degrees at the Poles.

Longitude is how far East or West you are, measured from Greenwich.
The scale is 0 degrees from Greenwich to 180 degrees in the Pacific, (which is also the International Date Line).

Latitude is the easy measurement, it can be measured from the Sun. Over a year, the midday sun moves in a measurable range according to the seasons. Your local height told you how far high (Equator) or low (Pole) you were.
Longitude was hard, until accurate clocks could be taken to sea. The clock was set to midday Greenwich, and your local midday was compared to it, with each hour difference being 15 degrees.

I hope this helps.

Jed

halo
11-12-2005, 14:58
thank's guy's

goose i want to start from the bottom,surveyor gave a good explination of what they are but what promted me to ask the question was my gps as they give bearings and location as lon/lat and not grid ref which is what i'm used to so was looking for some sort of tutorial,i take it that the degree number is how far n,e,w or south you are and the other would be minutes? please correct me if i'm wrong
as i dont know for sure.

anyway thanks for the replies guys

halo :)

Surveyor
11-12-2005, 15:59
Halo,
GPS units return a base value of Lattitude and Longitude as referenced to the WGS 84 ellipsoid (World Geodetic System 1984, a world wide approximation of the Earth's gravitational sphere).

So, a postition would be given as 09° 25' 34" N, 004° 34' 55" E, (in Degrees, Minutes & Seconds). That is Lattitude then Longitude (north then east), rather than East then North on a map.

To get the position as you have on a map, the WGS 84 position is converted to the local reference,(if needed) then projected on to the flat. That is, to go from an ellipsoid the size of the Earth, to an ellipsoid that best fits where you are, then flattened with the minimum distortion.

For Example WGS 84 converted to Airy Ellipsoid, then projected using OSGB 36 (Ordnance Survey Great Britian 1936) to give Eastings and Northings, the British National Grid.

Another is WGS 84 converrted to ED 50 (European Datum 1950), then projected on UTM Zone 32 V (Universal Transverse Mercator) for work in the North Sea.

Or simply, WGS 84 projected on UTM Zone 38 S. This would be an overlaid grid on existing local maps.

Your GPS unit has to be able to convert to the system your country is using. On the yellow Etrex, it is under Setup Units, for example.

Jed

leon-1
11-12-2005, 16:32
Halo, which GPS are you using??

I only thought that I would ask, as if someone here has the same model they could give you advice on it.

I have a Garmin GPS12XL and a Garmin EtreX Vista, but have also used Trimble and Magellan units. Both of the Garmin units have the facility to change from lon/lat to various different map datums for varying places in the world, they also have the facility to use both mils / degrees, Miles statute/nautical or Kilometers and Altitude in feet or meters.

Most of the Garmin models follow a similair setup so most anyone that has used one could give reasonable advice on it.

Is the gps designed to be vehicle based or handheld like the EtreX as I know little about vehicle based gps (I don't drive so have never found the requirement to use one), I tend to use a map.

halo
11-12-2005, 17:54
its the basic yellow etrex(if you can call a gps system basic that is)surveyor thanks for that but sorry bit too technical for me at the mo :eek:

Surveyor
11-12-2005, 19:46
Halo,
Well you are in luck. I take the basic yellow Etrex overseas with me. It comes in handy when trying to find one's way back to the boat/hotel when hammered.

To set yours to the UK Grid, go to the Menu page, it has a list with Mark, Waypoints, Routes, Tracks, Setup.
Click on Setup.

Then go down to Units, and select that.

The first Unit is POSITION FRMT.
Scroll this until you have BRITISH GRID.

The next one is MAP DATUM. (This may preset itself after setting the above option.)
Scroll through until you have found ORD SRVY GB

These two will set you up for UK maps. Though you do get a 10 figure grid reference the last two pair are metres, whereas, the first 3 of each make up the 6 fig reference. The letters eg TQ locate what block the grid is.

TQ 46785
BNG 89421

6 fig reference is TQ 467894

BNG means British National Grid. The figures in bold are the metres to 99m

The next option is UNITS, where you can set NAUTICAL, STATUTE, METRIC and YARDS.

Then NORTH REF, for TRUE, MAG GRID or USER.

Then finally, ANGLES. Here you have the choice of MILS or DEGREES.

I hope that this has you out and about.

Jed

Abbe Osram
12-12-2005, 08:44
its the basic yellow etrex(if you can call a gps system basic that is)surveyor thanks for that but sorry bit too technical for me at the mo :eek:

Hi mate,
I just ordered a yellow etrex and was asking myself how in the world I work with maps and gps together. It was clear for me that I could start walking, setting a waypoint and find back with the help of the gps, not needing maps at all.

But how can I pre-plan my travel working with a map setting waypoints which I want to follow later, that was my question? There are softwares which do just that, you sit down in front of your PC design your route, by clicking your path into the map, the software sets them as waypoints or routes, you give a name and export the route over to your gps. Now your Gps is guiding you along your pre-planed route without needing a map.

What is cool with that software is that you, at home, can plan exactly how long the entire hiking route will be and export it over to the gps.
I havent got my gps yet so I hope it works together, the PC software at home works great, lets hope that the etrex works together with it. You can too walk first around and set waypoints into your gps and when you are home again load the entire route back into your map software, there you can see where you actually walked.

I dont know if that is what you are after but for me it was a big question how to use the info from the gps with a map and got quite confused doing it. Now its easy.

cheers
Abbe

Ogri the trog
12-12-2005, 09:38
I didn't know how simple or complicated an answer to give, so I started with the dog basics.
Surveyor, erm, thanks for muddying the waters ;)
I was thinking of getting a GPS sometime in the future, but I think you've just put me off. I think I'll stick to the methods that I'm comfortable with - a printed map, a compass and a big slice of intuition :cool:

ATB

Ogri the trog

Platypus
12-12-2005, 11:08
Don't be put off by the tech talk, GPS is really easy and well worth the investment, (as long as you remember its limitations - batteries, tree cover etc.).

A lot of really good info can be found at the OS website (http://www.ordnancesurvey.co.uk/oswebsite/), but you may have to search for it.

Or even google "geocaching" for lots of info about GPS's and thier uses.

Goose
12-12-2005, 12:19
Halo, you don't really need to understand lat and long if you are using it in the UK, once it is set up for use with OS maps.
The grid system is a lot better and I am assuming that you can already use a map, 6 figure grids, bearings etc?
The link platypus gives to the OS site is a good one to revise the basics and terminology and you can use it in conjuction to the link below, it is an american site but it is pretty similar to our system.
The garmin link explains it pretty well how it works but don't think you have to take it all in, it gets a bit deep with different projections etc, but you should be able to find most of your answers there.
If you have problems setting up the GPS try asking at the shop it is the same with phones, it is a lot easier to understand how they work with a demo.

http://www.garmin.com/manuals/UsingaGarminGPSwithPaperLandMa ps_Manual.pdf

PS your question about degrees and minutes; A degree is seperated into minutes and seconds, http://id.mind.net/~zona/mmts/trigonometryRealms/degMinSec/degMinSec.htm
Basically degrees(minutes and seconds) are used to measure circles and spheres the earth is a sphere and the your bearing is measured by a circle, and the same terms are used in the measurements, a degree of bearing(direction) has no corelation to your position measured in degrees of lat. or long.

halo
12-12-2005, 16:59
cheers guys thats what i was looking for,surveyor bang on sorted now especialy
like the idea about finding my way back to the hotel when hammered but that will depend on how badly one eyed i am to see the display screen :lmao:
some top links there guys thanks :You_Rock_

paul(halo)

Surveyor
13-12-2005, 11:56
Ogri,
I do apologise for putting you off GPS, with the 'rocket science'. It was not my intention. I hope the following puts you back on GPS.

GPS will tell you where you are. It works with your map and compass.
It can store routes, and allow you to backtrack as well.

Imagine the world as a football covered in mud. That uneven mud is where we are, and cannot be easily replicated in maths. The football can be modelled in maths, and is the reference for GPS (WGS 84). The satellites overhead tell the GPS, where you are on the football. This is where you find the lat and long position.

The football may not be the best representation of where we live, so imagine a golf ball touching the inside of the football, where the UK is for example. That golf ball is the best representation of the UK.
Because the UK is long and thin-ish in a north south direction, a business card folded in half along its length and flattened back out, is the UK on a map.
The fold is the centre line over the UK and touches the golf ball over the UK, a light in the centre of the golf ball projects the UK onto the business card. Reading along the short edge gives Eastings, and along the long edge Northings.

The GPS knows where you are on the football, but now needs to convert this to the business card via the golf ball, and does a datum transformation to do so.

When using a GPS, all you have to do is know what settings are needed for where you are, then the figures you read are what you can plot on the map.

I hope that this helps you understand, and be more adventurous towards GPS.

Jed

Ogri the trog
13-12-2005, 12:20
Surveyor,
I was going to say don't worry with the appology. But having just read your entire last post, my brain is now dribbling out of my ear all over my shoulder :dunno:

There was a ditty in the mob about aircraft tactical nav systems - They know every place in the world. So if they know where they are not - then they can tell where they are. And if they know where they are not now, and where they wern't a while ago, they can tell you where they have been, where they are going and when they are likely to get to their next destination - which it can't tell you because its secret!

It sounds like me and PC's, once I'm used to doing something and get comfortable with it, I'll be OK - but for now it sounds a bit too involved ;)

ATB

Ogri the trog

Platypus
13-12-2005, 12:55
Since the beginnings of civilisation, man has looked to the sky to determine his whereabouts, taking the sun and the fixed patterns of the stars as his guides. Now constellations of man-made satellites have taken over as beacons to guide the way.

At the moment there are two global satellite navigation systems: the US Global Positioning System (GPS) and the Russian GLONASS system, both originally designed for military purposes. By 2008 Europe will have its own system called Galileo, which will comprise 30 satellites in orbit 23300km above the Earth.

Regardless of which system is used the principle is the same. The satellites each carry an atomic clock (the most accurate means of measuring time) and send this time-data out in the form of a radio signal. The signal is received by the user on his hand held device, which indicates the precise time the signal left the satellite and the exact position of that satellite. By reading the incoming signals the device can recognise the particular satellite, work out how long it took the signal to arrive and from this calculate the distance the user is from that satellite. Once the device has done this for at least four satellites it can calculate the exact 3D position of the user with respect to whatever datum the user wants.

All done by the application of a little bit of trigonometry and knowing the speed of light. :)