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Update Aug 2011
See the latest update at
the end of this page.
Update
Dec 2009
Since it is almost 10
years that I wrote this article and in view of the fact that it still
attracts many readers, I thought I should update. Also
prompting the update was the purchase of another GPS unit.
Details at the end of this page.
| This is a basic introduction on the subject of GPS & Computer
Mapping. |
Original article from Dec
99 with a couple of very minor updates along the way.
GPS is an acronym for Global Positioning System
and it is an extremely
accurate method of determining your position with the aid of a small hand
held receiver and 12 billion US dollars worth of satellites courtesy of the
USA Department of Defense.
The system comprises of 24 operational satellites with 4 satellites in 6
orbital planes spaced 60 degrees apart at an altitude of 20,200Km with an
orbital period of 12 hours. This allows for between 5 and 8
satellites to be visible at any one time.
There are also five land based sites to monitor satellite position and
accuracy of operational data and transmit correction signals to the satellites.
The five sites are located at Colorado Springs, Hawaii, Ascension Island,
Diego Garcia, and Kwajalein.
Position is calculated by the GPS receiver by triangulation of the data
from a minimum of 3 satellites. Three satellites will provide a
2 dimensional fix (latitude & longitude), 4 satellites are required for
a 3 dimensional fix (latitude, longitude & altitude).
Accuracy of the received satellite data is monitored by hundreds of
monitoring stations around the globe on a continuous daily basis and this
information is published on the internet. (See the link at the
bottom of the page)
I am more concerned here in discussing what to look for in the sort of GPS
you will find practical for use in a vehicle and bush walking, and how to
expand its usefulness enormously with the addition of a laptop computer and
some software.
The handheld GPS in itself is a very useful tool but used in conjunction
with a laptop computer it becomes an amazing piece of equipment.
There are several brands of handheld GPS receivers on the market with
subtle differences between them. I don't know of any bad models but some
are clearly more suitable for specific tasks than others. This
applies also to different models from the same manufacturer.
I will try to explain as briefly as possible what you would need to achieve
this and why you would bother.
You will need the following:
- A suitable GPS receiver (with a data port, preferably USB).
- A computer (a portable notebook/laptop is more versatile in this
application) with CD.
- Mapping software.
- Maps (simply paper maps that have been digitised (scanned) and placed on
a CD).
With this setup you can view very detailed maps on your computer screen and
your exact position (to better than 15 meters, even better in the USA, less
than three meters for WAAS GPS recievers) will be displayed by an
arrow superimposed on the map. As you move, so the arrow
position and direction on the map will move, constantly updating your
position. This is a true 'moving map' display.
There are many more features that I will discuss a little later.
A suitable GPS receiver will need to perform the following primary
functions. (Not all models of all brands have all of these features, in
which case, they will not be suitable)
- It will display alpha-numerically your present position in
Latitude/Longitude, UTM etc., on its LCD screen.
- It will also display other information such as velocity relative to
ground, direction if moving, distance travelled, information on satellite
position and signal strength, and time.
- It will allow you to store a limited number of locations of your choice
called 'landmarks' or 'waypoints'. (Waypoints and landmarks are
the same thing, waypoint being the nautical term.) It allows
you to form a limited number of 'routes' by utilising the
'landmarks'.
- It also performs another very useful function. As you move it
creates a 'track' or bread crumb trail to show where you have been.
This is displayed graphically on the screen. More on why this
is so useful later.
- It will also have a means of sending and receiving data to a computer via
an RS-232 serial connection or preferably USB for newer (after 2006)
computers.
The format of the data may be proprietary or it may be the industry
standard NMEA 0183. It will also accept an external source of power
to save on batteries. The necessary cable is usually purchased
as an optional extra.
- It will have some sort of cradle for mounting in a vehicle.
Also, usually an extra.
While almost any computer, desktop or portable, will do the job, the
following modest specifications are the minimum required.
- A notebook/laptop will much more useful in this application.
- Operating system should be Windows, ME or later.
- A Pentium II class processor or later (Pent II, AMD K6)
with at least 32Mb RAM, more is better.
- A CD ROM.
Update May 03 - I don't know of any new laptop computer sold today that
would not fulfill these basic requirements.
Update Jan 07 - Any computer sold today using MS Windows operating system
is more than adequate.
The mapping software allows the GPS and the computer to exchange data or
talk to each other and display the digital maps.
There is a number of software packages to choose from but I mostly use
Oziexplorer which uses non scalable raster maps.
The maps required are in a digital format and are either purchased on a CD
from a map shop or you can make your own.
Maps purchased on a CD are available in several scales, (50000:1, 100000:1,
250000:1, 1000000:1) and are put out by Geoscience Australia, the national agency for geoscience research and geospatial information. It is located within the Industry, Tourism and Resources
portfolio (formerly Auslig) and sold
through larger map shops.
Their 250K series is particularly useful and covers the entire continent
with over 500 maps on two CDs for $99-00. (May 03) This CD set
also contains a 240,000 place name database.
You can view a full size screen display of the map on
the right, just click here. This is exactly what you would see on your computer screen, the position
and direction of the arrow in the centre of the map is generated from the
incoming GPS data, always showing present position and direction of travel.
If you have a scanner you can easily create your own digital maps by
scanning paper maps or charts, which is exactly what your Geoscience Australia
maps are.
(I am not suggesting you attempt to scan 500+ large maps, but rather create
different scale maps of areas of interest to supplement the 250K Geoscience Australia
ones.)
Even the most basic 300dpi A4 scanner that sell for under $100 is suitable
since the maps will be scanned at 150dpi.
This type of map is known a raster format and is best viewed at predetermined
resolution as opposed to vector maps that can be "zoomed" in
without loss of detail.
To get this lot working is quite simple.
- You need to install the mapping software on your computer. This can
be done by downloading from the Internet or from a CD. Either way,
installation is trouble free.
- You need a physical connection between the GPS and the serial port of
your computer. The mapping software looks after the rest.
| How to use this setup in
practice |
You can use this GPS & Computer combination in two ways.
You can use it in the manner described but the problem is, most of us would
not have anywhere to put the computer while driving. My wife soon let me
know she wasn't going to nurse it for long.
The other and for most of us, a more practical way is to use the
combination for route planning before we set off each morning and download
that information to the GPS. Then just pop the GPS into its cradle on
the vehicle dash (or somewhere you can see it) and navigate directly from
the GPS screen.
This whole process is considerably easier than it probably sounds. I will
try to explain it as simply as it is in practice.
To plan your route for the day, just follow these simple steps.
- Connect the computer and GPS together with the data cable you bought with
your GPS, turn both on, then load the mapping software you had previously
installed. Place the CD containing the maps into the CD drive.
- Load the appropriate map from the CD (the software does this for you, you
don't have to sort through 531 maps manually).
- Click on the 'track' tool icon with your mouse, then place the mouse
cursor on the map where you want to start and then click with the left
mouse button. This will leave a 'track' point on the map. Repeat this along
the route you wish to take, placing a track point at every major bend of
the road until you reach your next destination. You now have a 'track' with
maybe a hundred or two points from your present position to your
destination, sounds laborious but it has taken less than five minutes so
far.
- Now, choose 'save track' icon to save this track to your hard disk, with
a name you can relate to later, such as "Trk20Mar01".
- Finally choose 'send track to GPS' icon and 30 seconds later, that track
is now displayed on your GPS screen.
As you follow your created track you are still leaving bread crumb trail
(which is where you actually went), which is being superimposed on the
track you created. If you wish you can just as easily save this new
bread crumb track on the computer with the 'get track from GPS' icon.
Why didn't I use the 'landmark' and 'route' feature ?
The reason being, while GPSs in this class can typically store 500
landmarks, only 30 can be used for any one route. Now this is OK for marine
applications where you can travel in a direct line between waypoints, but
not so suitable for road use.
By comparison, the same GPS can store 1000-1200 track points which can all
be used in one track if needed.
Also, navigating from a route means your small GPS screen is cluttered with
landmark symbols, making the route more difficult to follow, unless you
turn them all off which would include any significant ones you may need to
see.
I like to reserve the use of landmarks to save the position of points of
interest or main features only, not minor points along the way.
| Additional
features provided by the computer |
The mapping software provides some very useful extra features not usually
available to the GPS only.
- The ability to be used with any scale of map, from a world scale to a
street level scale, from digital maps you can buy to paper maps you have
scanned.
- You can make your own digital maps of, for example, a series of forest
tracks, by downloading your bread crumb tracks and including your own
labels and comments.
- You can add to any of your maps, landmarks, comments and even
photographs.
- You are not limited by the memory constraints of your GPS, good as it
might be, to the number of landmark or track files that you can save.
Because all of your data is stored on the computer you have no limits
whatsoever.
- You have full editing control of all landmark and track point attributes.
You can shift a single track point or landmark or an entire track with the
mouse. To shift a single point, all you have to do is place the mouse
pointer on the point and drag to the new location and the software looks
after updating the data files.
When on holidays, I download my GPS generated track file every day and
therefore have a permanent record of every metre I have travelled for later
reference. The saved tracks and landmarks can be displayed on
any of your maps.
This landmark and track information can be readily shared with others by
email etc.
Also, it is worth considering the safety benefit of knowing exactly where
you are when traveling in remote areas. (It relieves your
navigator of the chance of her getting you lost.)
|
How much does this all cost ? |
The most expensive item is the computer. A perfectly
suitable model costs from $800. Generally speaking,
these days, even the most basic new model will be more than adequate.
$500 in 2011 is all
you need to spend.
(The computer has many other uses while traveling such as sending and
receiving email in conjunction with a mobile phone, storing all those
photos you have taken with your new digital camera, keeping a record of
your travels, etc.)
GPS receivers with all the necessary features complete with a vehicle
mounting cradle and power & data cable start from $400 (Jan 07).
The software and the excellent Geoscience Australia maps are
presently just under the $100 mark each. (May 03).
It is often useful to display other points on a map such as location of UHF
CB radio repeaters and TV transmitter locations to determine if any are
within your area.
See my TV Reception
page for information regarding displaying TV locations on Oziexplorer maps
and email me for files to enable displaying UHF repeater sites.
|
Map capable handheld
GPS units and software.
|
Dec 07
These mapping GPSs use scalable vector maps
To replace my eight year old Magellan 315 which could fail at any time now
due to a non replaceable memory backup battery, I have just purchased a Magellan
eXplorist 400 which was packaged with a mounting cradle, cables, cigarette
lighter 12V plug, 240VAC adaptor and Next
Destination's DiscoverAus Street & Track Topo maps on an SD memory
card.
Why an eXplorist 400 ? I just wanted a
basic USB compatible GPS and this package was on special and seemed
ideal.
Unfortunately, this is where to story ends - for
now. While the eXplorist works as expected, the SD maps
from Next Destination were
unusable. All map data on the SD card was corrupt and
unreadable.
It will be returned to Next Destination Pty Ltd with the expectation of a
replacement under warranty. Fortunately Next Destination Pty
Ltd is an Australian company based in WA so warranty claims should not be a
problem (if they are I will certainly let you know).
The eXplorist in conjunction with Oziexplorer worked OK although
not at all convenient to upload and download tracks, waypoints and routes
as was the old 315 but as a mid range GPS it's not a bad unit.
As soon as I receive a replaced or re-written SD card, I will continue this
article with detailed look at the eXplorist range and the Next Destination
maps.
My apologies to those to whom I promised to have this article completed
before Christmas.
Jan 08
The SD card was replaced by the local retailer. Of the four units
they had in stock two were also faulty, hardly inspiring much confidence in
the product.
Also, in doing a software/firmware upgrade from Magellan's web site, I lost the Magellan
Australia base map. It
seems there was supposed to be a warning attached to the GPS not to do this
but mine did not have one nor did any of the others in the store.
Next Destination saw this
as a good opportunity to extract another $95 plus postage from me to reinstate
the lost base map (which is something one should be able to do on line at no
cost).
If you have a Magellan GPS, be warned, it uses some software/firmware that can not
be backed up (even Microsoft don't do that) and you will have to cough up to
get it back again.
My opinion of Magellan... good hardware, shame about the software and as for
the local support.............
Would I buy another one ? No, my next GPS would most likely be a
Garmin.
My personal opinion only, compared to the Aust agents for Strong and Dvico
whose products I have and recently upgraded firmware and software, Next
Destination were a disappointment, I hope I never have to make a warranty
claim.
In fact, learned friends of mine have always purchased on-line (not eBay) and
saved a bundle, around 50%, by bypassing the local distributor. But
choose the brand of GPS carefully, local distributors policy and charges vary
greatly should you need any repairs.
Other friends, heavily into
geocaching, have a preference for Garmin GPSs.
TIP . . . Choose a GPS that doesn't use or need a memory backup battery,
often those 10 year lithium batteries aren't. If that
battery needs to be replaced, assuming it can be without ruining the sealed
case, expect to pay $150-200 and in some cases even more.
Dec 09
For a while I had been considering purchasing a new GPS and had my eye on a
Garmin 60CSx. I had selected this one for many reasons, it features a
bright high contrast colour LCD display, flux gate compass, barometer/altimeter,
quad helix antenna and most importantly, the SiRFstarIII receiver chipset.
I also liked the layout with the keypad below the screen and all at the
front - good ergonomics.
By sheer accident and good luck, I discovered that Garmin had quietly
dropped this chipset and are now using Mediatek MT3329 chipsets (to save a few pennies
and / or due to SiRF loosing a patent infringement case brought by Broadcom
which may have negative ramifications for GPS manufacturers ?).
Fortunately I managed
to located a SiRFstarIII equipped 60CSx and promptly snapped it up.
In handhelds, Garmin has only used this chipset in their top-of-the-range
models, the 60Cx, 60CSx, 76Cx and 76CSx, not on the 60, 60C, 60CS, 76C and
76CS, nor the Oregon, Dakota, Colorado, eTrex etc..
(Garmin coding - C=colour, S=sensors (compass and barometer) x=accepts additional
memory in the form of uSD cards)
However, I may be doing a disservice to Garmin and Mediatek, the
SiRFstarIII is 20 channel with -159dBm sensitivity compared the Mediatek
MT3329, rated acquisition 66/tracking 22 and -165dBm sensitivity - better
on paper so far but it's very hard the get the full specs, besides, the
SiRF has the track record.
I have had a bit to do with satellite navigation systems during the last
twenty five years but the sensitivity of this 60CSx really surprised me.
In comparison of signal acquisition with my Magellan 315, which isn't too
shabby and Magellan eXplorist 400, there isn't any, this 60CSx is in a
different league.
In doors, it will have a strong signal from seven or eight satellites
compared to absolutely none from the others, very impressive.
I have even maintained a fix in our local shopping centre underground car
park 30 meters from the entry ramp.
Used in a vehicle in a predominantly vertical position, the
quad helix antenna is superior the the patch / ceramic patch antenna which,
in most GPSs, favours a near horizontal position.
I had considered, briefly, the touch screen Garmin Oregon and Dakota as
well as the Magellan Triton 500 but the 60CSx was a clear winner for me.
The Garmin is supplied with their Mapsource software which enables up and
downloading maps, waypoints and tracks to your computer.
The 60CSx, as with all other map capable Garmin GPSs, has a world wide base
map which for navigation purposes is, to be kind, inadequate.
You really need to invest in some maps. Garmin have their propriety
topo maps and street maps both of which are routable and provide turn by
turn instructions.
There is also some third party maps, one being OzTopo at around $260 and
some free maps from Shonky Logic and Tracks4Australia (T4A).
Don't be put off by the name, Shonky maps are excellent, many prefer them
to the others.
Even the much smaller T4A, a 39Mb download, may be all that many will need
and are particularly well suited to mapping GPSs with limited non expandable
memory. (The screen shot on the right shows my 60CSx with the T4A map
selected and on the left, a Shonky map selected. )
I suggest that before you go spending $200-300 on maps, try the Shonky
and/or T4A maps, they're good quality and free.
Be aware that
the $200-300 maps are locked to the unique ID of your GPS (not the serial
number) and can not be be uninstalled and put on any other GPS.
In other words, if you lose, damage or replace your GPS, you will have
to purchase new maps. You may be able to install your maps on multiple
computers (varies with map supplier) but only one GPS.
(If your main interest
is navigating urban areas, an in-car style GPS would be more suitable starting from around a third of the price including
the map and with a larger
touch screen, some are even splash proof. Some high end
ones can use raster as well as vector maps.)
A good mounting cradle
is important if the
GPS is used in a vehicle or boat. For the 60 series, the
Garmin cradle is a joke, not much better than hanging the GPS from the rear
view mirror with a piece of string.
For not much more, the excellent
RAM mounts are the way to go.
This is a very versatile and durable
modular system, an excellent product for mounting GPS, phone, PDAs etc.
If you change your GPS etc later, you only need to replace one part of the
mounting, the base and swiveling part is retained.
Update
Aug 2011
Fortunately, I had resisted the temptation to spend $200+ on maps, relying on
the perfectly adequate Shonky map in conjunction with a 5 meter contours
overlay, also free (contours from Contours Aust), shown above.
(This combination roughly equates to the commercial 250K Geoscience Australia
maps for useful detail.)
In recent months I have downloaded street level mapping from OSM Australia at http://www.osmaustralia.org/
There are several map set covering all Aust including routable ones providing
turn by turn instructions. Examples of these free maps are shown
here that are the actual display from a Garmin 60CSx.
(Routable maps of most countries are available
on-line elsewhere.)
All these maps can be
viewed and manipulated with Garmin's MapSource on a computer and loaded
into your Garmin GPS (depending on the model).
There are a number of excellent programmes that you can download to this
end, Garmin's MapSource, BaseCamp, MapInstall, nRoute also cgpsmapper, MapSetToolKit
and GPS Babel for converting
between various proprietary file formats.
While the urban
mapping detail is comprehensive, its presentation on a small screen does
not compare to a dedicated vehicle GPS with its larger screen.
The trade-off is, a handheld such as the 60CSx is highly portable, comparatively
rugged,
water proof, has excellent reception in adverse conditions (due to a
premium receiver chipset and helix
antenna) with good battery life and many features not found in most
dedicated vehicle GPSs. These are the Swiss army knife of
the GPS world.
With a programme like Garmin's nRoute on your laptop computer, you can do
real time navigation on the big screen as well.
Individual maps or a combination of maps can be displayed on Garmin GPSs
such as the 60CSx as well as on your computer.
The Garmin 60 series
has been superceded by the 62 series, cosmetically very similar but with
some relatively minor but worthwhile internal enhancements.
The picture below, is part of a computer screen dump from MapSource with OSM street
map. This is the same level of detail you will see on your
Garmin GPS. Although the level of detail is identical,
different versions of MapSource and nRoute and different GPSs will render
the map differently also some detail will vary depending on the level of
zoom chosen.
For further information click on these links to other web sites. GPS
primer
Monitoring
site info
Geoscience Australia
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