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g'day all,
I've had a quick scan thru the archives to see what I missed
whilst I was away.
Under umpteen subject headings the accuracy of Global
Positioning System (GPS) units and getting lost was discussed.
Follows are some musings...
1
Sometimes, after I 'mark' the position of my vehicle and
before setting off, I just for the hell of it hit the "Go to" button to
this same spot.
Frequently I get a reading of 0.1km ....and I repeat I
have not moved a cm ! Try it.
However this can be improved if I use the averaging facility
on my Garmin GPS II plus. My Magellan GPS 300 does not have this
facility.
2
Why have two GPS units ? The cheaper GPS300 is set to lat/long
and is used only for atlassing readings. The more expensive and better GPS II
plus is used for navigation and set to read UTM (grid reference) figures which
are easily calculated on 1:100,000 scale maps. (Each 1cm square = 1
km)
Here a good % of the roads on the map aren't there ....and
many of the roads that are there, aren't on the map !
I regularly use the GPS bread crumb map facility to correct my
map. Also, the bread crumb trail is an alternate and perhaps a better way of
getting a feel of where you are in relation to where you started.
3
I am envious of the longer shadows down south and the moss
that is supposedly grows on the south side of the trees in Vic.
4
I often use the moving shadow method to determine compass
direction. Mark the end of a shadow and wait for say 15 mins and mark the
new location of the end of the shadow. A line thru the two points runs east-west
and the shadow (in Aust) is on the south side of the line.
On the 21st Mar and Sept the line is exactly E-W...at other
times the line is close enough.
(But I've often wondered if the shadow is to the north at Cape
York in the middle of summer, when the sun is over the Tropic of Capricorn
?)
5
Do not think the sun always sets due west. It
varies considerably from Winter to Summer.
6
A cheap wrist compass is good enough for me. K-mart in their
camping gear section sell for about $8 the Coghlan brand. I took it
off the supplied band and slipped it permanently on my watch band. My first one
lasted at least 2 years before it fell apart.
7
And lastly know how to ident the Southern Cross and how to use
the pointers to determine True South. It helped me on one 25km overnight walk
home after my mate's vehicle ran out of tyres.
8
I have input lat/long for all the local towns/cities up to
1000km. So when atlassing I let the GPS tell me how many km (as the local
Aust Raven flies) and direction to the nearest town (But as BA strangely (?)
want to know how far from the town I have to add/subtract 180deg) (Although one
visiting atlasser told me I should be using road distance
!)
9
Rather than getting the lat/longs from the internet I
used Dick Smith's "GPS Location Guide"
10
Buy, read and understand an Australian Bushcraft
Book...preferably one approved by the Aust Scouting Assoc.
11
One of the reasons that the USA switched of the varying GPS
error was that there was a way of getting around the problem. Surveyors etc had
a base station for which the position was accurately known. They compared that
position to what a GPS at the base said and continuously radioed the error to
the GPS unit in the field. Some sort of black box unit spat out
the corrected Lat/Long figure.
I hope that is not too confusing.
Regards, Bob Forsyth, Mount Isa, NW Qld.
PS To use the same "Subject" and maintain the thread,
click the reply button, delete all or what can be eliminated of the
previous message and replace the "To" address with that of
Birding-Aus.
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