Yahoo Over 55s Bushwalkers

Using Map, Compass & GPS

Each year we usually have one walk dedicated to training with map and compass.

  1. Use a compass to walk toward a given bearing.  This is a team of 4 exercise and one team member walks foward as far as possible (and still be seen by the compass holder) to lock-in a position on the bearing "line".
  2. Set a compass using a destination identified on the map (See the note below).

Map Reading Guide

A useful reference is  - UserFiles/Compass/How-to-use-a-Map---Compass2.doc - How to use a Map & Compass.

These notes are useful for point 2 above - Set a compass to walk from point A to Point B.

GPS Units for hiking

The maps we use, Bibbulumn Track, Munda Biddi Trail and Dept of Environment & Conservation maps, use the GDA94 (Geocentric Datum of Australia) specificaions, Grid coordinates: (Universal Transverse Mercator, using the GRS80 ellipsoid), Map Grid of Australia 1994 (MGA94), and based on Ellipsoid: GRS80.  Each map will show this reference just below the "Scale" on the map using words similar to this.

Set your GPS to use this system.  For my GPS, I go to Tools, Settings, Navigation, Primary Coordinate System (choose UTM), Primary Coordinate Accuracy (choose 1 or 10m), Primary Map Datum (choose WGS84).  My GPS can also display a "secondary" coordinate system which I set to Lat/Lon, but I never look at it.

 Langford Park 5 June 2014- a good example of use

 A group of 23 walkers travelled 5 km north of Langford Park trying to follow the Bridle Trail markers.  Some markers were missing, and we reached a point where we decided to turn back.  We had a Parks and Wildlife map (Department of Environment and Conservation, Jarrahdale & Yaganing)  We were able to pin down exactly where we were by reference to our GPS reading which said we were at 410,826mE and 6427,728mN (UTM references)

 The main UTM Eastings and Northings are blue lines exactly 1km apart.  Pinpointing where we were was therefore quite easy.   It was helpful having a Draftex scale rule with a 1:25 and a 1:50 scale. (See Other Resources – More on maps)

 

UTM - Universal Transverse Mercator Geographic Coordinate System

Partly from http://geology.isu.edu/geostac/Field_Exercise/topomaps/utm.htm

The idea of the transverse mercator projection has its roots in the 18th century, but it did not come into common usage until after World War II. It has become the most used because it allows precise measurements in meters to within 1 meter.

Mercator Projection

 

A mercator projection is a ‘pseudocylindrical’ conformal projection (it preserves shape). What you often see on poster-size maps of the world is an equatorial mercator projection that has relatively little distortion along the equator, but quite a bit of distortion toward the poles.

 What a transverse mercator projection does, in effect, is orient the ‘equator’ north-south (through the poles), thus providing a north-south oriented swath of little distortion.

   

 

 

By changing slightly the orientation of the cylinder onto which the map is projected, successive swaths of relatively undistorted regions can be created.

 

This is exactly what the UTM system does. Each of these swaths is called a UTM zone and is six degrees of longitude wide. The first zone begins at the International Date Line (-180°, using the geographic coordinate system).  This is just east of New Zealand.   The zones are numbered 1 to 60, from west to east, so zone 1 begins at the International Date Line and extends to 174°W. The last zone (zone 60) begins at 174°E and extends to the International Date Line.


The zones are then further subdivided into an eastern and western half by drawing a line, representing a transverse Mercator projection, down the middle of the zone. This line is known as the ‘central meridian’ and is the only line within the zone that can be drawn between the poles and be perpendicular to the equator (in other words, it is the new ‘equator’ for the projection and suffers the least amount of distortion). For this reason, vertical grid lines in the UTM system are oriented parallel to the central meridian. The central meridian is also used in setting up the origin for the grid system. 

 

Any point can be described by its distance east of the zone origin, its ‘easting’ value, and by its ‘northing’ value, the distance from the equator, or from the “south pole”, the latter qualified by having the equator set at 10,000,000mN (see note below).

 By definition, the Central Meridian of a zone is assigned a false easting of 500,000 meters. Any easting value greater than 500,000 meters indicates a point east of the central meridian. Any easting value less than 500,000 meters indica

tes a point west of the central meridian. Distances (and locations) in the UTM system are measured in meters, and each UTM zone has its own ‘origin’ for east-west measurements.

 

 To eliminate the necessity for using negative numbers to describe a location, the east-west origin is placed 500,000 meters west of the central meridian. This is referred to as the zone’s ‘false origin’. The zone doesn't extend all the way to the false origin.

The origin for north-south values depends on whether you are in the northern or southern hemisphere. In the northern hemisphere, the origin is th

e equator and all distances north (or ‘northings’) are measured from the equator. In the southern hemisphere the origin is the equator, but nominated as a false northing of 100,000,000m, and all northings are measured from there, decreasing towards the south pole which is almost the zero point. Having separate origins for the northern and southern hemispheres eliminates the need for any negative values. The average circumference of the earth is 40,030,173 meters, meaning that there are 10,007,543 meters of northing in each hemisphere.

UTM coordinates are typically given with the zone first (eg, 50H), then the easting, then the northing. So, in UTM coordinates, Dwelli

ngup is located in zone 50H at 412,112m E (easting), 6,379,987m N (northing). The comma separators are not always shown.  The UTM system may seem a bit confusing at first, mostly because many people have never heard of it, let alone used it. Once you’ve used it for a little while, however, it becomes an extremely fast and efficient means of finding exact locations and approximating locations on a map.

Many topographic maps published in recent years use the UTM coordinate system as the primary grids on the map. The UTM grid is usually shown as blue lines across the map with blue numbers in the margin.  The grid coordinates in degrees, minutes and seconds, are often shown as well; black numbers in the margin

, against black lines just 4mm in length.

Zones around the world

 

 In the above map, UTM zone 1 extends from Longitude 180 degrees to Longitude 186 degrees.    UTM zone 31, extends from Longitude 0 degrees to Longitude 6 degrees.

Notice that zone 50H covers the south west of WA 

 


Dwellingup in zone 50H

Latitude

Longitude

-32.71438

116.0622

-32ᵒ 42’ 51.8”

116ᵒ 3’ 43.9”

Easting

Northing

412 112mE

6 379 987mN

Altitude = 266m above sea level

 

Unfortunately, the conversion between “Grid Coordinates” in degrees and UTM coordinates in metres is not a simple calculation and is best

done using references on the internet, or in your hand held or vehicle GPS.

 

 

 What if there is an important feature "between maps" ??

An area of "overlap" is provided.

 

As an example, the map above shows the “overlap” between zones 10 and 11 to cater for features “on the border” between zones.

 

Please let me know if you find a better explanation of the UTM system - Mike

See also www.dtpli.vic.gov.au/__data/assets/pdf_file/0010/111043/The_Map_Grid_of_Australia_1994_Computational_Manual.pdf