||This page will give information to
assist you in learning more about GPSrs. It is intended to be simple and
informative, only covering details which should enable the reader to recognise
uses of these little handheld gems. It is not model specific, but describes
functions which exist in a GPSr, and with practice, the reader can adapt the
information to any model.
CAN THEY BE USED FOR?
A GPS receiver (GPSr) can be used
to identify your current location to an accuracy of 4m or less, tell where you
have been and tell you where you need to go. They can be connected to a computer
and data can be transferred both ways. Data collected can be overlaid onto a map
to show graphically where you have been. They can calculate areas of fires, show
sunrise and sunset, moon cycles and even the best times to go fishing. They can
store the location of hazards, water tanks, dams and structures, in fact
anything you wish to enter (or "mark").
||SO HOW DO
receives signals from satellites and by calculating the difference between the
time the signal is sent and the time it was received, it can calculate its
distance from the satellite. Using at least 4 satellites, it can then work out
its location on the earth's surface! This signal is generally not affected by
clouds or weather but may be affected by very dense foliage, cliffs and solid
The GPSr MUST have acquired satellite
reception before it is useful. A common mistake is to read the location from the
screen before it has locked onto satellites; the location being shown will still
be where it was last time it was used! A message should indicate "ready to
navigate", "3D NAV" or similar. Be aware some models use the message "tracking
satellites" when trying to locate them, whereas other models use this message to
indicate it is using them...beware! Become familiar with your model.
GPSr is not a compass. A GPSr is only valid for navigation and direction when it
is moving. After all, it does not know which way you are holding it, but it
tends to assume it is facing with the aerial pointing in the direction you are
||....wait,tracking satellites! We cannot read our current
location from this GPSr!
||This one now ready to
navigate and gives our location
A GPSr is not manufactured to be
country specific and will work anywhere in the world. As such it comes with an
inbuilt list of "formats" under which it can display information. This can be
latitude/longitude, British grid, German grid, NZ grid, many other country grids
In Australia, we should set our GPSr to either "lat/lon" OR
"UTM/UPS", depending on who will be using the data. Pilots often work with
"lat/lon"; firefighters tend to use "UTM", which is what we commonly use with
our topographic maps to give our usual "6 figure grid reference".
can change the format at any time...it does not affect the stored data, only the
way it is presented. A GPSr can actually be used to convert UTM readings to
lat/lon (and vice versa) if needed!
should I do about DATUM?
you intend to use a GPSr, it is important you establish what datum it
is set at. If you give someone a grid reference "off a GPS" they should
ask you "under what datum is that?" and you need to be able to tell
them confidently the setting! As we have recently received all new GDA
maps in the Hawkesbury we should use the newer GDA datum setting.
If you have a GPSr without this you can use WGS84 instead.
If you go out and use a
GPSr to collect data in the field, plot dams, structures and the like, ensure
you also record the datum setting in the GPSr at the time. As long as it is
known, programs can be used to convert this information to other datums.
...that's about it for this lesson. When you have all that sorted,
email me and I will put up the next one, dealing with all those numbers
on the screen
Any questions, email me at Pete's GPSr Page or take a look at what I do with my GPSr! So
far I have located over 1000 of the critters! When there, enter
postcode 2753 into the top right hand corner box ("zipcode") and see how many are