Navigation:
When navigating to a destination on a non-autorouting GPS unit, the unit will simply point you in the right direction using an on screen arrow and tell you how far you have to go to get there (i.e. 6.2Km with a compass arrow pointing North). Imagine now that you are (on a road) traveling North to get to your destination when you come to a T-junction where, if you turn left you will head West and if you turn right you head East. Your GPS is telling you to carry on 5.4Km’s Northwards. Which way do you turn?
Obviously, this again depends on your application. If you were walking in the middle of the African bushveld with no fences, roads or rivers in the way, you would have no problem. Driving around the farming districts in the Freestate and Northern Province may however, get you a complimentary load of buckshot in your butt for crossing private property without permission.
An autorouting unit, on the other hand, will direct you via the most optimal route (according to your settings), selecting the correct roads and then giving you turn-by-turn directions on how to get there. The ETA (Estimated Time of Arrival) feature on these units will also take into account the speed limits of the roads when working out your traveling and arrival times.
Search & Lookup Features and POI (Points of Interest):
All map enabled GPS units have a POI search feature (the database is built in to the detailed maps loaded to the unit). The points of interest consist of restaurants, petrol stations, shopping centers, police stations, hotels, hospitals, sports stadiums and much more. You will be able to do a search for the nearest clinic or hospital for example, or find the quickest route to a train station without knowing the specific street address.
Routing Setting, Avoidance & Via Points:
All autorouting GPS units will give you a range of routing settings to choose from – from ‘Quickest Time’ (only selecting main roads and freeways) and ‘Shortest Distance’ to ‘Offroad’ (straight line ‘as the crow flies’). You can choose to avoid Toll-Roads, Dirt Roads or Freeways and avoid making U-Turns. With the ‘Area Avoidance’ features (on the higher end models) you can also choose to select areas, from a house, suburb or even entire towns and cities, demarcate them and set the unit to avoid them at all times. This is handy when traveling through Gauteng and avoiding the dodgy suburbs, townships and high crime areas for example.
When creating a route from point A to point B, it is also possible to add in Via Points. In other words you may want to travel from point A to point B stopping at points C, D and E along the way. Points C, D and E are added to the route as Via Points after the route from A to B has been created. The GPS unit will then either work out the best route between A and B including all other Via points in between or allow you to visit them in the order that you specify.
Tracklog & TracBack:
Tracklogs are made up of data gathered automatically from your motion while the GPS is turned ON. They provide a record of where you’ve been, and when, so you can later determine your path and speed. There may be hundreds or thousands of such points in a track, but they are all anonymous. They don’t have names and you can’t easily get the location of any particular one.
If you use Garmin’s TracBack function (available on most handheld / outdoor units), it will turn a track into a route that goes in the opposite direction. This is done by analyzing the path of the track and placing automatically created waypoints at significant turning points in the path.
Mapping:
Many users require a GPS unit, not for navigating but for mapping (creating maps). Mapping of farms, game farms, property boundaries, fences, roads, positions of buildings, windmills, towers and other infrastructure. There are a couple of points to consider when using a GPS as a mapping tool but the most important point is the accuracy requirements of the project.
How accurate is my GPS?
Most manufacturers will state the accuracy figures for their GPS systems as <15 meters (under 15 meters), 95% typical (95% of the time). What this effectively means is that for 95% of the time (an averaged figure I might add) you may indeed be accurate to within 10-15 meters as usually shown on the screen, however, the other 5% of the time (again… averaged) you could be out by up to 30 meters. I say ‘could’ because, as mentioned before, this is an AVERAGED figure. The algorithms within the software are designed to cut out the (high and low) peaks and work out the accuracy of every point calculated on the number of points taken over a period of time (remember that with a one second update rate the GPS is calculating it’s position every second). There are also many other factors that can affect the accuracy of a ‘Recreational Grade GPS’ receiver.
GPS vs. DGPS:
In DGPS (Differential GPS) operation a station, often called a beacon, transmits correction data in real time that is received by a separate box, called a beacon receiver, which sends the correction information to the GPS receiver. In principle this is quite simple. A GPS receiver normally calculates it position by measuring the time it takes for a signal from a satellite to reach its position. By knowing where the satellite is, how long it takes to send the signal, and knowing the speed of the signal it can compute what is called a pseudo range (distance) to the satellite. This range must be corrected before it is used to compute the final position. Corrections such as compensation for ionospheric errors due to the fact that the ionosphere slows down the speed of travel of the radio wave are one form of correction that can be applied.
A DGPS beacon transmitter site has already calculated all of the pseudo range correction data based on the fact that it already knows exactly where it is and can compute the errors in the satellite computed position from its known location. Once the pseudo range correction data is computed it is sent to the GPS and used to compute a more accurate fix.
Map Creation, Map Editing & Map Restrictions:
Another factor to consider when using a GPS to make your own maps is the map editing software to be used. Garmin map enabled GPS units are bundled with the MapSource map viewing software program and either City Select maps or Garmap maps, or both. However, these map software programs are more suited to navigation applications and can only be used to ‘create maps’ in the most rudimentary sense. You cannot for example ‘draw’ in a road, boundary or fence on the map. These can only be created by using the tracklog features and will be displayed (as an ‘overlay’ on the map) as a series of points (a ‘breadcrumb’ trail) and not as a solid line. It is also not possible to give this ‘road’ a label or name. Buildings, towers and windmills are easier to capture and display since they will only consist of one waypoint and they can be given a short name or ID number.
There are a number of commercial (and expensive) map editing programs to be found (and even one or two reasonably good free ones floating around on the Internet). With all of these programs it must be remembered that they all tend to be highly specialized (i.e. complicated to learn how to use them) and time consuming and most people would be better off hiring a professional to do the job as this would end up being quicker and, in most cases (especially where time is money) cheaper in the long run.
Please could you provide the names of these programs — Commercial as well as the free ones that you mention , as well as the relevant URLs.
I am very interested in the technology and have the time and expertise to work it out.
Am I reading correctly that GARMIN are NOT players in this market ?
Many thanks