3 Methodology¶

3.1. App Structure¶

3.1.1. Use Cases Diagram

In the Figure bellow is the developed Use Cases Diagram that represents the possible interactions of different actors (User, Vital Jacket, Data System and Doctor) within the system. This diagram shows the requirements for the development of the app.

!Use Case Diagram CMEB.pdf!
Figura 3.1.1.1. Use Cases Diagram.

3.2. Algorithms Step Counting¶

Having the values from the accelerometer which has a FREQUENCY OF __, the acceleration from the 3 axis in condensed in the acceleration magnitude:

mag = sqrt(x^2+y^2+z^2)

Then, in order to remove the gravitational acceleration, the average acceleration is subtracted:

netmag = mag - avgmag

so the netmag represents only the acceleration regarding movement. The algorithm works as follows:
The time-netmag graph is divided in dynamic 3-sample windows. The values of these samples are tracked and if they are in crescent order, the system registers the first sample as the start of a step. When a value is detected above a pre-defined OR DYNAMIC threshold, all values above that threshold are saved in a vector, PeakVector. When the values of netmag drop below the threshold, the system uses a 2-samples window to track the slope of the magnitude. If the second value is greater than the first, it is considered the start of a new step, thus ending the previous one. Since the PeakVector contains all the values that fall above the step threshold, the maximum value should represent the real peak.

3.3. Design and Functionalities¶