GPS usage and accuracy

To: "Birding-Aus" <>
Subject: GPS usage and accuracy
From: "Irene" <>
Date: Mon, 15 Oct 2001 16:16:00 +1000
(Have been trying to send this email for 2 days - hope this one gets through !!)

Hi Vicky

I sent the following emails to birding-aus early to mid last year - I thought 
they would still be on the birding-aus archive.
In any case here they are.  Particularly note:

(1)  The book recommended by David McDonald is fantastic.
(2)  Not sure how experienced you are with GPS or how much you've looked at 
your instruction book - I can vouch that it is
EXTREMELY important to set up the GPS properly in terms of such things as 
"track up" or "north up", alarms for return to
site, degree/minute/second alternatives, initialisation (perhaps this is what 
is throwing yours out by so many metres,
because most times the EPE estimated position error should only be a max of 5 
metres) and Datum such as WGS or AUS/AUD.  So
if you haven't already done so, I'd suggest a good few sessions making your way 
through the instruction book and thoroughly
checking all your settings.  (Sorry if you are one of those rare people who has 
already bothered to look at the instruction
(3)  The book recommended by David also explains something that may be throwing 
your accuracy out by so many metres
(depending on the period of time you are talking about), and that is the 
Selective Availability.  Our "civilian" GPS are
dependent on big governments etc. "allowing us access" to the satellites that 
provide the readings.  With the terrorist
activity and air strikes, USA may have set the Selective Availability so that 
it purposely "throws out" our GPS by up to 100

Cheers and Happy Times with Nature

Irene Denton
Concord West, 12 km from Sydney city, NSW Australia
33°50'17"S  151°05'25"E

-----Original Message-----

As you can tell through recent emails, I bought a GPS in April and extensively 
used it through my Queensland trip in May.  I
originally asked for guidance so that I would know how to use ALL of the GPS 
functions rather than spending the money on a
GPS just to use it for lat/long readings.  I have now come into contact with 
many people who have bought a GPS in the last 3
years to do bird atlas sheets, and only use their GPS for lat/long.

What a shame!!  These gadgets can be great fun, and useful in many other ways.  
Some examples are:

* Can be used to clock speed - either of the vehicle you are travelling in, or 
the speed you are walking at.  So if you're
trying to get to a particular walking destination by a particular time, this 
will tell you whether you're keeping up the
pace.  I clocked budgies flying next to our vehicle at 62 km ph.  There's a 
total trip odometer plus "short" trip odometer in
GPS also so you can track how far you've gone.

* Can tell you distance from your current location to a place.  Though remember 
this is GPS distance (ie straight line as the
crow flies) as it can't work out whether you have to walk around a lake to get 
to your destination.  Nevertheless this can be
useful.  Using routes can also tell you GPS distance between two points (which 
I have used now to tell some people, eg, how
far Mitakoodi Gorge is from Cloncurry, being reasonably accurate as the road 
was reasonably straight).  If you've broken down
and are wondering how close it is to town ......

* Plotting where you've been can be interesting and fun.  On the tracks 
(laughingly called roads on the maps) near
Urandangie, we went too far and had to do a bit of a loop to get to where we 
wanted - the plot screen clearly showed our
roundabout route.  This plot can also show your own wanderings in case you want 
to backtrack.

* GPS even calculates the time of sunrise and sunset.  So if you want to get 
somewhere and set up tents before dark, the GPS
will tell you sunset at the location.  Want to know when to get up in the 
morning to chase the birds, well there it is.  This
is very useful if you are moving large distances in a day.

* On one road, the map showed the road going pretty due east.  Sure enough, the 
GPS showed that for many many kilometres, we
remained on a strictly due east heading.

* One night we were discussing whether we were on a line with Alice Springs - 
no problem, get out the GPS, check latitude
(because my GPS has the lat/long of several places pre-keyed in) and we were 
able to answer this question.  And at one stage
in Queensland I could see that I was almost exactly due north from home.

* And yes, even though you shouldn't totally depend on GPS for navigation and 
to get you out of a jam if you get lost, using
the highway, compass and plot screens can be useful and interesting.

So, for anyone out there who has a GPS but doesn't use it much, or for those 
people contemplating the purchase of one, I'd
recommend you "get into it" as these gadgets can be great fun.

Irene Denton
Concord West, 12 km from Sydney city, NSW, Australia
33 50' 17" S  151 05' 25" E

Another Message:

Hi everyone
There was a call recently for GPS recommendations and I recommend the Magellan 
GPS 315 that I purchased in April for $480.
You may recall I asked earlier this year about GPS and how to use them, and a 
great book was recommended at the time.
Particularly I wanted to learn more about GPS rather than merely use the thing 
for straight lat/long readings for bird
Well I took my GPS on my Queensland trip and for an entire month I thrashed it. 
 Every day I very actively used virtually
every single function and screen of my GPS, working my way through all the 
navigation screens, changing settings to see how
they would work etc.  I took turns at turning the GPS on and off constantly 
during the day and also just leaving it on for
several hours at a time.  I also pretended a few times that I was lost and used 
the navigation screens as the book told me
to - they got me back to camp each time.  I used the GPS walking, and also on 
the bus at speeds of up to say 90 km per hour.
Used it on open plains, amongst taller gum trees and amongst spinifex and 
mallee.  Even played with it at night for fun.
I couldn't be happier - the Magellan GPS 315 worked very well.


Response from Colin Clarke:   "I'm *lost* for words. Most useful comments I've 
seen, by far."

And a third one:
I recently asked for help regarding resources on “how to use a GPS”, as I 
wanted to be able to use much of its functionality
rather than merely use lat/long readings and easting/northing readings.  Many 
of the responses I received from people were
very helpful.

Many thanks for David McDonald’s advice regarding the book by Lawrence Letham 
“GPS Made Easy: Using global positioning
systems in the outdoors', 2nd edition, Rocky Mountain Books, Calgary, Alta, 
1998”.  I was able to obtain a copy of this book
(the last one that Paddy Pallins, Sydney had, $24.95).  This book is FANTASTIC 
and I thoroughly recommend it.  It was exactly
what I was looking for, written in plain English, step by step, so that you 
could really understand what all the numbers and
terminology in a GPS mean.  More than this, it explained UTM measurements on a 
map (and different formats for these), the
various latitude/longitude formats (and their presentation on maps) etc. etc.   

It had good explanations as to when you might, or might not, use certain 
features of the GPS.  With excellent complete
illustrations and examples to work through, I think I now understand some 
70-90% of my GPS’ functionality, rather than only
10%.  Thanks David.

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