U T M or LAT/LONG

Submitted: Tuesday, Jan 28, 2003 at 22:20
ThreadID: 3132 Views:2351 Replies:5 FollowUps:13
This Thread has been Archived
can anbody help with info on the differance between LAT/LOG & U T M any info will help .I can change my GPS to either but how do I know what my map is . drive safety MAL/B
Back Expand Un-Read 0 Moderator

Reply By: OziExplorer - Tuesday, Jan 28, 2003 at 22:30

Tuesday, Jan 28, 2003 at 22:30
Mal, I only use UTM (Univeral Transverse Mercator) for all the right reasons.
Can you post an e-mail address and I will send you comprehensive information on the two systems and where to find all the information about UTM. The great thing about UTM it is all meaningful and in metric.

Basically, UTM is for land lubbers, and Degree, Minutes and Seconds is for the water lovers.
AnswerID: 12033

Follow Up By: Brian - Tuesday, Jan 28, 2003 at 23:13

Tuesday, Jan 28, 2003 at 23:13
And fly boys
0
FollowupID: 6951

Follow Up By: Member - Richard- Wednesday, Jan 29, 2003 at 04:08

Wednesday, Jan 29, 2003 at 04:08
Ozi, you say you use UTM "for all the right reasons" How did you arrive at this decision. Please tell me. Prove to me that LAT/LON is no good.
I think if you research the matter you will find a lot of land navigation is done with LAT/LON. Why is LAT/LON not meaningful and if it is not meaningful why do most Hema maps and our own David use it. Are you telling me they are wrong?
Dick
0
FollowupID: 6961

Follow Up By: David - Wednesday, Jan 29, 2003 at 09:57

Wednesday, Jan 29, 2003 at 09:57
Ozi,

I wouldn't mind getting this info and I am sure a lot of others would like it too. Maybe you could post it on this site?
0
FollowupID: 6972

Follow Up By: Member - Mal B - Thursday, Jan 30, 2003 at 10:55

Thursday, Jan 30, 2003 at 10:55
oziexplorer could you list the info onthis site may be the others could use it also safe driveing MAL/B
0
FollowupID: 7026

Follow Up By: Member - Mal B - Thursday, Jan 30, 2003 at 10:56

Thursday, Jan 30, 2003 at 10:56
oziexplorer could you list the info onthis site may be the others could use it also safe driveing MAL/B
0
FollowupID: 7027

Reply By: Slunnie - Tuesday, Jan 28, 2003 at 23:59

Tuesday, Jan 28, 2003 at 23:59
Yeah,

UTM will give you a grid ref that can be read off 1:250,000maps etc and because of the scales and lines on the maps, I tend to think are more accurate. The marine bunch, of which I have been guilty, use the lat/lon measurements which will also give you a position, just using a different method. I do notice that many GPS refs given on land, by both guide books and maps are also given as lat/long measurements, which in a GPS will be equally as accurate as using UTM. Military folk I think also use UTM as do bushwalkers etc. Horses for courses matey, whatever you prefer. With my GPS (Magellan 315) I can have a primary and secondary co-ord system, and have UTM as primary and Lat/long as the secondary, so depending on the map I use, I can flick between the two, though keep an eye on the map datums!

Regards
Slunnie
AnswerID: 12044

Reply By: mad mapper - Wednesday, Jan 29, 2003 at 10:47

Wednesday, Jan 29, 2003 at 10:47
Hi there

UTM stands for Universal Transverse Mercator - it's both the grid coordinate system and the projection used on all topographic maps. The Australian equivalent of UTM is AMG (Australian Map Grid) or the new MGA (Map Grid of Austraila). Like one of the replies said it's very logical once you get to use it as it's all metric so this makes distance calculations between points quite easy. Points are given in Eastings and Northings. One catch with UTM is that you must know what UTM zone you are in or your position can be out by hundreds of metres.

Latitude and Longitude is the original system developed centuries ago and is still the standard particularly in marine circles. These positions are given in degrees minutes and seconds - just like time, 60 seconds in a minute etc. The earth is divided up into 180 degrees east or west of Greenwich and 90 degrees north or south of the equator.

There are 3 issues to be a aware of when using your GPS with your map. These all affect the mathematical calculations used to convert the curved 3D earth into a flat 2D map:

1. Map Projection eg Universal Transverse Mercator (used for most world maps), Lambert Conformal Conic, Simple Conic etc. (NB A projection can not be set on your GPS)

2. Coordinate System - UTM or Lat/Long - this is a personal choice when it comes to waypoints and it's up to you what you use. The map you're using your GPS with will in reality determine which one you will need to use. UTM is only useful on a map up to 1:250,000 as beyond this it becomes very inaccurate as the square grid can no longer account for the curvature of the earth. That's where lat/long comes into it's own and that's why most regional maps use lat/long.

3. Map Datum eg WGS84, AGD66, GDA94 etc these datums are related to the Australian Survey height controls. There is a 200m shift to the north east between AGD66 and WGS84. WGS84 and GDA94 are basically identical with only a few centimtres between them.

I know that it a very mumbo jumbo summary but there is lots to it as you can see. The best thing to do is just go out for a few hours use your common sense and nut it out for yourself.

There are also some good cheap books on all this available from your local map shop.

Have a great day

Rob

AnswerID: 12064

Follow Up By: Brian - Wednesday, Jan 29, 2003 at 17:38

Wednesday, Jan 29, 2003 at 17:38
Rob maybe you can tell me why the datum you use makes a difference when useing lat long??? Untill recientlyy I was under the impression that there was no datum other than greenwich and the equator
Brian
0
FollowupID: 6990

Follow Up By: Greg Harewood - Thursday, Jan 30, 2003 at 01:41

Thursday, Jan 30, 2003 at 01:41
Brian - Greenwich is not a Datum in the modern sense. It was chosen a century or two ago as the point through which the line of 0° Longitude should pass through. This was when you had to measure angles to stars etc and know the time to figure out where you were (relative to Greenwich or some other place e.g. Paris). Times have changed - co-ordinates today relate to mathematical models based on datum’s (points within the earth) and spheroids (mathematical model of the earths shape). If you change the datum (or Spheroid) you use you will get different Co-ords. No big deal - just be aware what was used to calculate the co-ords you are using (and remember that some were calculated using Stars/Sun/Planets and Greenwich/Paris etc and do not relate directly to modern datums).

While I’m here..On the other subject ...In my opinion for the average 4WDriver it doesn’t really matter if you use Lat/Long or UTM. I find if using a map that’s it’s heaps easier to locate points using UTM with scale rule and therefore enter them into GPS using same. If you're just navigating using a GPS and/or using 250k+ scale maps it makes no difference – the scale of the map and the GPS inaccuracies take care of that. If you were using more accurate equipment (eg DGPS) and/or working on a scale less than a metre or two you would NOT be using Lat/Long – depends what you up to. Geocache co-ords are all in Lat/Long and I find them (as one would expect) to be more than adequate.
Cheers Greg
0
FollowupID: 7012

Follow Up By: Brian - Thursday, Jan 30, 2003 at 11:04

Thursday, Jan 30, 2003 at 11:04
Greg I understand about the need for datums when using UTM but still don't see the need for it in Lat long . What datum did CptCook use????
It may well be that I will have to accept the they are and move on.
It has just got my cuirousity up???
Thanks for the reply Brian
0
FollowupID: 7030

Follow Up By: Brian - Thursday, Jan 30, 2003 at 11:38

Thursday, Jan 30, 2003 at 11:38
http://www.icsm.gov.au/icsm/gda/faq.htm#greenwich This goes some way to explane it.
Brian
0
FollowupID: 7034

Follow Up By: Greg Harewood - Thursday, Jan 30, 2003 at 11:46

Thursday, Jan 30, 2003 at 11:46
Brian - It does get confusing - Especially if you start mixing old with the new.... Anyway - Captain Cook used angles to stars/sun and planets and time to calculate his position relative to Greenwich. They didn’t have datums as we use today. Modern equipment (eg GPS) doesn’t utilise Sun/Stars etc - its not accurate enough - so complex (for me) maths has been employed. Datums are points with different x,y,z values and are an integral part of the calculation of your position. Datums are used both for Lat/Long and UTM etc calculations. A different datum will give you different Co-ords. Again.. you just have to know what datum is used. I doubt whether any modern datum would actually result in 0° Longitude exactly passing through Greenwich anymore – though it would be pretty close - its just a historical thing now and of no consequence to modern navigation.
Cheers Greg
0
FollowupID: 7038

Follow Up By: Brian - Thursday, Jan 30, 2003 at 11:59

Thursday, Jan 30, 2003 at 11:59
I am begining to see the light ! According to that web site 0° is 100m east of grenwich now.
When using ONC maps what datum do I use,as it does not state the datum???
Brian
0
FollowupID: 7040

Reply By: Member - Andrew - Wednesday, Jan 29, 2003 at 18:09

Wednesday, Jan 29, 2003 at 18:09
As I understand it Brian the datum is very important if you wish to be accurate with your navigation. A lot of countries use a fixed known point upon which all mapping data is measured from. Can you imagine if Australia used the Greenwich meridian as a point to measure all their mapping points from? We are so far from it that a little error might creep in by the time the tape measure waas moved a few thousand times around the globe!!!!! Thus we have our own datum (don't ask me where it is--- Perhaps Sydney or Canberra. There are also several Aust datums. They generally start with WGS***
AnswerID: 12091

Follow Up By: Slunnie - Thursday, Jan 30, 2003 at 02:02

Thursday, Jan 30, 2003 at 02:02
AUS** x2 isn't it?

Regards
Slunnie
0
FollowupID: 7013

Follow Up By: Member - Andrewpatrol - Friday, Jan 31, 2003 at 19:45

Friday, Jan 31, 2003 at 19:45
Yes could be Slunnie, sorry maybe i got that wrong.
0
FollowupID: 7118

Reply By: Member - Mal B - Thursday, Jan 30, 2003 at 10:46

Thursday, Jan 30, 2003 at 10:46
thanks for the info looks like in need to read more .U T M looks easier to use ie almost like a melway. safe driveing MAL/B.
AnswerID: 12143

Sponsored Links

Popular Products (13)