The Global Positioning System

An Aid to Light Railways Research

Note, this article is from Light Railways No.146, April 1999. Since that time the price of GPS units has fallen substantially from the $A600 to 700 quoted below.

The nature of light railway research and, indeed, much of the fun of it is the outdoor activity that goes with it. Hour upon hour of desk-bound work delving through old newspapers, official records and interviews is an essential ingredient to well researched work. However, equally important, is the on the ground mapping and `deciphering' that goes with working out the broad picture of tramway operations as well as its detailed `whys' and `wherefores'. Having the right tools is a must in order to maximise the information gathering that goes with this activity. Much of the enjoyment comes from the looking and discovery process, but by having good gear with you and using it systematically you can add to the enjoyment and create a valuable record that can be analysed and put into context later. The traditional tools of a light railway `bush-basher' (excluding food, water and a suitable snake deterrent - a big stick) include topographical maps, compass, notepad, tape measure and machete. In recent times pedometers, altimeters and inclinometers have also come into a price range within reach of most researchers and can prove most useful.

Unquestionably though one of the most useful tools to come within reach of your average researcher in recent times has been the Global Positioning System (GPS). There are now many units on the market and, although they each have their differences, they all track American global positioning satellites. The system has been in operation for around a decade for military, shipping (air and sea) and emergency service use but the cost of tracking devices has prevented widespread use by private citizens until recently.

Most good quality units cost $600-700 and will track between 5 and 12 satellites continuously. The accuracy of all however is limited to within 100 metres on 90% of occasions. This is mainly because of a deliberate `wobble' placed in the satellite signals by the Americans to prevent someone else using their system to lob `nasties' at them with considerable accuracy.

The removal of the wobble, however, is scheduled within the next 2-3 years. This will greatly increase accuracy, but if you keep in mind that most of us use 1 in 25,000 maps to record findings, even with the wobble, specific positions determined by your GPS unit will presently be within 4mm of the true location on the map most of the time! Less expensive units are available but beware that some of the lower cost units do not work well under tree cover (not much good in the bush!).

The principle item of information the units provide is the grid reference of your present location. This can be recorded in the unit along with a description and referred to later. Most units will, however, do much more. Several have a `Tracking' function which records continuously where you have been. This can prove very useful if you have been following a tramway for sometime. It allows you to map as you go and download to your PC later.

Most have the capacity to prerecord a location you wish to reach. As you move towards that point the unit will continuously tell you, no matter where you are, what the bearing and range is to your desired destination. This has proven very useful recently when trying to find my way back to a particular spot in the bush at Big Pats Creek. The unit guided me straight to within metres of where I needed to be without any fuss at all. In doing so it saved me perhaps an hour of bashing around looking for signs of my previous visit.

Most units will tell you how far you have travelled and your altitude (with considerable inaccuracy!). Back tracking function is also useful at times. It will direct you back over the route you have followed including any turns. It is good to know you can find your way out again!

I personally have two units (you can never be too careful! - just joking). My older unit (a Silva) does not track as many satellites as my more recent acquisition (A Garmin 12XL) but it has features that are still not available on any other unit and has proven immensely valuable.

The usefulness of both units was demonstrated just recently. The Silva has a Navimap attachment that allows you to calibrate any map and by using a puck, select and record specific locations. I used this feature along with the Garmin to solve a problem I have been scratching my head about since 1983.

After the Ash Wednesday bushfires of that year I came across what turned out to be a logging tramway along the Mississippi Creek out from Warburton. The problem was it disappeared into a recently bulldozed logging coup and could not be followed to its source. The issue was whose tramway was it? The mills in the area were well known and were marked on official maps, but recent logging activity had destroyed much of what remained. This tramway, however, led to none of them. So what on earth was this tramway doing pointing in the direction it was? My GPS units provided the answer to the conundrum. I selected the nearest mill to the log tramway and determined to test its given location. On the ground the tramway, for geographic and gradient reasons, could not have served this mill given its stated location. Early aerial photographs clearly showed the mill as the usual white `blob'. Without roads to provide reference points, however, it was difficult to translate the blob to a modern map. But, the aerial photo did contain two other points for which precise location details were known.

The photo was placed on the Navimap device attached to my Silva GPS unit just as you would place a map and calibrated using the two known points. A click on the blob and I had the precise longitude and latitude of the mill. The photo was removed and replaced by a modern day map showing the official location of the mill and the plot of the tram found in 1983. After a quick re-calibration I brought up the mill's location as found from the aerial photo. The puck was run across the map until it indicated it was pointing at the mill site.

Surprise, Surprise! It showed the mill as being well to the east of the location on official maps, and directly in line with the heading of the mysterious log tramway. Problem solved!

Lesson; don't trust maps completely. They can be wrong. The final step in this little saga was the transfer of the mill location to the Garmin. A journey out into the area had the Garmin beeping at me telling me when I was within 100 metres of the mill. Sadly there was nothing left to see, but it did point me to the precise location of the tramway, which had been very difficult to find after the post-fires regrowth. Overall it has been a very useful addition but only as an extra tool. The traditional tools of machete and compass, coupled with eyes and brain, continue to be the most valuable instruments as ever.

Mike McCarthy