I mean, what reference coordinate did you use to compare?”
The questions touch on several critically important aspects of any positioning system and even more of those for indoor positioning systems:
There are many questions like this. They are related to each other, and it is vital to understand in detail how positioning systems work and how to assess them. Let’s discuss the points one by one.
Greenwich meridian or GPS/GLONASS coordinates are irrelevant when discussing indoor positioning systems (IPS) because your premises are indoors. The premises or the IPS can be anywhere – in Nairobi, underground in Canada, or on Mars – and if the IPS doesn’t have a link to an external coordinate system (a sort of geo-referencing), the system cannot calculate which part of the world it is even in theory. It can be anywhere.
Imagine you are in a closed room without windows. Your robot is precisely driving indoors using, for example, Marvelmind Indoor Positioning System. But you cannot measure which part of Earth you and your robot are in – the windows are closed. While you were driving inside, the aliens stole you from the Earth and transferred you to Alpha Centaurus. If you haven’t experienced acceleration, you can’t say whether you stayed or moved or are being moved at that moment and with what speed.
Something similar is already happening to us in real life – not in a hypothetical case with aliens – but in real life and every second. We believe we measure our very accurate coordinates against the Earth. At the same time, the Earth is flying several km/s in space against the Sun, and our solar system is flying with several tens of km/s against the center of the galaxy, etc. What are my coordinates? Against what?
Thus, we establish that coordinates are always relative.
What does the Marvelmind indoor positioning system use as a relative point?
Our system is designed, first of all, to guide an autonomous robot from point A to point B. Of course, the same applies to autonomous drones, forklifts, or even people tracking. All these cases are the same for this discussion. But for the sake of simplicity, let’s discuss autonomous robots.
With this approach in mind (driving from point A to point B), it does not matter what the absolute distance between point A and point B measured in meters is. Even when we say “absolute distance,” – it is not absolute. It is a distance related to some arbitrarily chosen distance unit – a meter. It could be in meters; it could be the lengths of the robot; it could be in some units of our indoor positioning system.
For precise autonomous drive or precise indoor positioning, it is crucial that the system can very precisely and very accurately measure the coordinates of mobile beacons. Coordinates in the coordinate system of stationary beacons. Not in meters. Not in some GPS coordinates but in the internal coordinate system of the stationary beacons. Because we know the coordinate of point A in internal coordinates, the coordinates of point B in internal coordinates, and the robot’s current location in internal coordinates. So, internal distances, coordinates, and dimensions matter – not some “external meters” or external coordinates.
Here is how it works in practice on an example of a mobile robot:
When you already have an indoor positioning system up and running, your robot is ready to drive because the robot has coordinates of point A, point B, and its current coordinates. The robot’s autopilot will compare the expected location (the next desired waypoint) with the robot’s current location and drive the robot accordingly.
What is essential, the robot doesn’t need to know the distance in meters. Everything is measured in some internal units – inside the coordinate system inside the indoor positioning system. Not in meters.
Why do we focus on this so much? Why do we stress that the absolute distances do not really matter and even harm sometimes when mixed with internal measurement units/distances:
Therefore, it is important to distinguish between relative and absolute distance clearly. It is essential to understand that “absolute” space is not absolute either – it is the relative distance measured in something else – platinum meters, the revolution of the wheels, etc.
Summary and key points:
Remember, the Marvelmind Indoor Positioning System is, first of all, designed to drive a robot from point A to point B. To be very accurate in doing that, we need to have as little dispersion of the measurements of the location of point A, point B, and the robot’s current location as possible.Option 1 has higher distribution but a lower average shift against (0,0) coordinates. Whereas, Option 2 is relatively more accurate but has a bigger absolute change against the (0,0) point.
Once again, an absolute shift from an expected point measured in meters or some other measurement units outside of our coordinate system doesn’t matter. We must make exact measurements inside the system: for point A, point B, and the robot’s current location. Then, we will be able to drive from point A to B very accurately and return very accurately, and it doesn’t matter whether it takes us 10.000m or 10.200m to go from A to B. Therefore, when we drive, we bring the robot to point A and measure its position very accurately. Then, we move the robot to point B. It can be shifted against some external coordinate system, against an external grid – it doesn’t matter. After we moved the robot, we again recorded the measured location of point B in our indoor positioning system. And now, we want to drive back to the original point A as precisely as possible. The correct choice would be Option 2 because it is relatively more accurate, and it doesn’t matter that it is shifted in the external coordinate system.
Therefore, we are perfect if you want to use Marvelmind RTLS for autonomous driving or flying. If you’re going to use us as an alternative to a laser distance meter – only with calibration and a clear understanding of the limitations (air temperature, first of all).