Estimote is hesitant to disclose their indoor navigation algorithm, but from the looks of it, a triangulation algorithm makes the most sense. In this chapter, we will learn how a triangulation algorithm can be used for indoor navigation. The topic is necessary because if you know the theory behind the working model of indoor navigation, you can come up with your own implementation of the algorithm and build your very own Bluetooth system. 

Triangulation is a concept of trigonometry and geometry. It is a process of estimating the location of a point by forming triangles to it from the location of known things. We will take a simple room example to explain how triangulation can work in an indoor location. In order to implement triangulation in this room, imagine that each wall has a Bluetooth beacon dedicated to it (as Estimote recommends):

The triangulation will work best if the room is triangular, but since that is not the case, it is recommended you use one beacon for each wall. Now imagine the signals from a beacon, which are omnidirectional, and a cellphone representing the user, for a setup such the following:

Based on the signal strength, the user can be anywhere in the purple circles. So it is not possible to know the location of the user based on just one beacon. But now imagine a scenario where two beacons are doing the same thing:

Since now we are receiving signal strength data from two beacons, we can roughly estimate that the location of the user is somewhere in the blue ellipse. The location is not yet successfully determined, so we will take the approximations from the other two beacons too:

By using all the four beacons in the room, we can approximate a very reasonable location (red ellipse) of the user. By adding beacons, we will increase the accuracy, which is what Estimote recommends as well. 

The same method is used to find the approximate location of an earthquake's epicenter and the presence of a user in a cellular network. Using triangulation, you can implement your own indoor navigation. Another useful method of determining approximate location is called trilateration (working with distances instead of angles), but it is less accurate indoors. The best-case scenario is if we combine the two methods to refine the location.