simple Graph Data Analysis, detect peaks, Detect Rowing Stroke

Question

I have problem with determinate when new stroke is done at Sport Academic Rowing.

• I need simple algorithm which to detect moment, which characteristic are one global valley, then big rising which end with peak( look at picture 1 - catch phase, immediately after vertical dotted line

• The algorithm needs to be “adaptive”, because when you are rowing hard, the highest point is much higher than when you are paddling and reverse.

• Input: float acceleration Data is from accelerometer, so because of that data come continuously. I can find timestamp too.

• Target: That is cyclic graph, so i want to find how much cycles(strokes) are made per minute, for that i need to detect each one. (period between each two vertical dotted lines - - -)

Rowing boat acceleration vs time graph:

Thank you

Answer 1

Looking at the data, a simple algorithm could be to divide acceleration into three distinct regions:

• less than -9 m/s^2
• between -9 m/s^2 and 0 m/s^2
• greater than 0 m/s^2

Then you construct a state machine with two states to detect each stroke. The first state is triggered when the acceleration is less than -9 m/s^2, and the second state is triggered when the acceleration is greater than 0 m/s^2. When the acceleration is in between, it doesn't change the state.

With your data, at 89.5s, it enters state 1, then enters state 2 at 89.8s, then state 1 again at 91.1s, etc.