Some Thoughts about Geo-Positioning

Today every phone and tablet and a lot of other devices have capabilities to detect the current location and this can be used for many things… Even some speedometers for bicycles rely on geo-positioning only or use a rotation count of the wheel just as additional, optional source of information.

In the 1990s I worked in a company that provided management systems for public transport, which included radio transmission, schedule tracking, information display for passengers, information for drivers etc. An important ingredient was knowing where the vehicles were, or even better, when they passed a certain point. This seems to be mathematically equivalent, but when the vehicle moves at different speeds, stops at traffic lights and bus stops (or tram stops or subway stops) then the time of passing at a location cannot easily be found from the location at a certain time without loss of accuracy.

To understand things well: At that time GPS was already there, but it was deliberately made inaccurate for everyone who was not the US-military. This could be improved by putting an additional GPS-device at a fixed, well-known position and by applying the deviation found by this device to the measured positions of the mobile GPS devices. But some more sources where used. The vehicles usually moved along predefined routes. These were measured with a special measuring vehicle, which required someone with excellent knowledge of the bus routes to participate in measuring the distances between the busstops and for the whole line. In this case there were formal bus stops, which were stored in the software systems with scheduled times for each run and of course exact distances. And between there were informal stops which are marked with some sign and recognized by the drivers, with times being somehow between the scheduled times at the surrounding formal stops. Distances could vary, because depending on the daytime different routes for the same line could be planned. But for the specific vehicle on a specific run, in principal its exact route, the distances between formal stops and the arrival and departure times at the formal stops should be well defined internally, up to the second. Even though published schedules only show minutes. So, this adds another useful source of information, because the vehicle itself also measures the distance, maybe a bit less accurate than the measuring vehicle, but hopefully accurate enough to be useful. That is kind of the opposite of what current bicycle speedometers do, using the real measured distance and speed to learn about the position rather than the position to learn about speed and distance. Of course, bus drivers are humans, they make mistakes and when a new routing has been implemented they might miss a turn or so. Not very often, but it can happen. Also a driver might make a little detour and stop at a coffee shop to get a cup of coffee (of course take-away). But 99.5% of the time the distance measuring should help.

Yet another source of information are the stops and the door opening events, especially in conjunction with scheduled travel times and distances. Of course, the door can in rare cases open even without a stop. And more often, informal stops can be skipped, if nobody wants to get of or on. And stops can occur because of traffic jam and because of traffic lights. But even about these there can be some knowledge. This is yet another source of information.

The most reliable source of information are beacons. These are devices that are positioned at certain fixed points where a lot of vehicles pass by. Ideally in such a way that on each route at least once a beacon is passed. And they provide the more interesting information, when the vehicle passes them, not where the vehicle is at a certain time. Unfortunately these beacons were expensive, so they could only be used in small numbers as an additional source of information.

Today the concept of finding one’s position is quite mature. But we should not forget that companies like Samsung or Google can spend millions on developing hardware and software to do this really well. For a small company which is fighting with software delivery schedules, different client requirements, legacy software, and of course very limited budgets, doing a good geo-positioning by combining many insufficient sources of information to get a decent accuracy was quite a challenge. A lot of ideas to improve this, that where „obvious“, would be moved to some far future releases that never actually happened. For example, the system could learn distances and travel times between stops by observing the system for a few weeks and even include informal stops. And different sources of information could be combined in sophisticated ways, not by just using the best information or some kind of average or so… I am sure the developers did a good job.

So what happened: Today we have several sets of satellites for geo-positioning. Galileo was launched to get more accuracy and to be independent of the deliberately inaccurate American GPS. And the Americans stopped making GPS inaccurate and even removed the feature from newer satellites. At least they say that they did. There is a Russian, a Chinese and a Japanese system and some more. So current phones and speedometers can and do use all of these simultaneously to get fantastic accuracy. It is said that Google observes WiFi names and uses that as an additional source of information. What could be used, are the antennas of the mobile network. At a certain location a certain number of antennas can be seen and the strength of the signal can be measured and be used in conjunction with knowledge of obstacles, orientation of antennas and their transmission power to improve location finding. I do not know if this is done and if this would be of any help for improving accuracy. What could also be used are sensors in the devices that observe acceleration. And of course, beacons can now be any kind of object that is sufficiently unique and that is at a fixed position and can be recognized by a camera with some images recognition software. In case of bicycle speedometers or in case of public transport vehicles, using the wheel rotation as measurement for the distance and using that as additional source of information could still be useful, especially in tunnels, where the satellites are not helpful. When it comes to the third dimension, elevations, mountains or just human built structures, the satellite positioning can be used even for that. But the air pressure is an additional source of information, especially in conjunction with weather data and with data about the location of elevations and artificial structures. Then it can even help knowing about the position, unless it is located in a flying object.

It can be seen that this is an interesting area and even though the accuracy is already very good today, some further improvements would still be useful.

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