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GPS & Computer Mapping

This is a basic introduction on the subject of GPS & Computer Mapping.

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 (typically around 35 x 65mm).

- 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.

- Preferably with a colour screen rather than a monochrome one.

- Operating system should be Windows 95, 98, ME, NT2000, XP 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 adaquate.

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 Ozexplorer. 

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.

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.

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.

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 or floppy disk.

In addition to the list of top spots in the 'Travel – Destinations' page I will email the Waypoint data file to any one requesting it.   This will enable you to use these waypoints without having to type them in.   As this list grows, with your contributions, this will save a lot of time and eliminate inevitable typing errors.

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.

(The computer has many other uses while travelling 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).
 

  

Other Useful Info

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

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, it doesn't rate a mention. 

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.