Map Coordinate Systems

Hi Phillip,
It is a very straight forward answer. The paper maps that you have, have both lat/long coordinates and grid reference details. There is no way that you can change what is already printed, so you change the set up in your GPS to the system that you work with.

If you are handy with the GPS, you should be able to plot your course, the the point where you would like to camp, transfer these details to the GPS, and then let the GPS do all the work, using the "Go To" feature. This will then keep you and your party on track and guide you to the exact spot to where you would like to camp.

Cheers and happy hiking

Stephen

Phillip,
Somewhere on the map border, sometimes on the bottom below the scale bar but at least on the bottom border of the map you should find reference to the Horizontal Datum. Often in Australia if the map is a few years old it might be Australian Geodetic Datum 1966. It could also be WGS84 or GDA94. Whatever the datum, that's the figure you should find in the set up menu of your GPS (It could be under Units in the menu if the GPS is a Garmin) and select. That way your GPS and your map are in sync. Make sure you put the correct datum in.

Also, most times the "projection" is Tranverse Mercator or UTM. Make sure you select the correct projection information listed in the same area of your map and select that in the set up menu of your GPS if you want Eastings and Northings displayed as opposed to Lat & Long.

Good luck
Toolman

I'm happy with Stephen & Toolmans replies above Phillip but I've had same issues in odd circumstances and some software like Ozi-explorer doesn't work or calculate correctly under some unusal circumstances and I need use the following approach.

There is a large formula that can do what you wish , but for small distances you can take shortcut below.

Assume a degree of latitude and a degree of longitude represent a constant distance at any point. So you can say that 1 degree north equals 666m and 1 degree west equals 999m etc . YUo must find these constants at your location.

(Note - the actual figures I use above are not correct and just for illustration as my memory ain't that good)

Assuming your reference doesn't have it . get the UTM reference which is in meters from another GPS or whatever and write it on each map corner, along with Lat/long.

Subtract Lat/long from a line between two corners , and also the UTM .
Divide one by the other and you come up with the ratio of degrees to meters for both lat and long.

Using this rule of thumb you can relate one to the other directly.

You can also quickly calculate distance at any angle by squaring out the sides as per phythagorus (did I get that name spelling even close?)

Robin Miller

Can i ask what GPS unit you are using that ONLY gives Lat/longs?

The main grid you see on your map will more than likely be shown as UTM (or UTM/UPS) on your GPS under the projection settings. As has been mentioned previously, also make sure the datum of the map is the same as the display setting on your GPS.

If you are unable to estimate the location between the lat/long grid, use a lat/long ruler printed from sites such as http://www.maptools.com/pdf/LLTools/LLRules.pdf, or http://www.caves.org/survey/gss/latruler.pdf ...good instructions for these free tools are available here ==> www.maptools.com/FreeTools/

One thing to remember is that it is much more simplistic/traditional to use the map to navigate, and use the GPS as a waypoint location device (don't forget to store the waypoint of your vehicle, the campsite before walking). a GPS receiver by itself (no map) without any waypoints is more or less useless.

Andrew