How do you implement a Highpass filter for the IPhone accelerometer?
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02-07-2019 - |
Question
I remember seeing the code for a Highpass filter a few days back somewhere in the samples, however I can't find it anywhere now! Could someone remember me where the Highpass filter implementation code was?
Or better yet post the algorithm?
Thanks!
Solution
#define kFilteringFactor 0.1
static UIAccelerationValue rollingX=0, rollingY=0, rollingZ=0;
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {
// Calculate low pass values
rollingX = (acceleration.x * kFilteringFactor) + (rollingX * (1.0 - kFilteringFactor));
rollingY = (acceleration.y * kFilteringFactor) + (rollingY * (1.0 - kFilteringFactor));
rollingZ = (acceleration.z * kFilteringFactor) + (rollingZ * (1.0 - kFilteringFactor));
// Subtract the low-pass value from the current value to get a simplified high-pass filter
float accelX = acceleration.x - rollingX;
float accelY = acceleration.y - rollingY;
float accelZ = acceleration.z - rollingZ;
// Use the acceleration data.
}
OTHER TIPS
Just in case someone wants to know, the highpass filter can be found in the Accelerometer Graph sample.
Here's the link, i was looking for this one too. This is an example for adaptive / non adaptive highpass and lowpass filter: Apple iOS Reference Library - AccelerometerGraph Example
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