AccelerometerGraph/AccelerometerFilter.m
/* |
File: AccelerometerFilter.m |
Abstract: Implements a low and high pass filter with optional adaptive filtering. |
Version: 2.6 |
Disclaimer: IMPORTANT: This Apple software is supplied to you by Apple |
Inc. ("Apple") in consideration of your agreement to the following |
terms, and your use, installation, modification or redistribution of |
this Apple software constitutes acceptance of these terms. If you do |
not agree with these terms, please do not use, install, modify or |
redistribute this Apple software. |
In consideration of your agreement to abide by the following terms, and |
subject to these terms, Apple grants you a personal, non-exclusive |
license, under Apple's copyrights in this original Apple software (the |
"Apple Software"), to use, reproduce, modify and redistribute the Apple |
Software, with or without modifications, in source and/or binary forms; |
provided that if you redistribute the Apple Software in its entirety and |
without modifications, you must retain this notice and the following |
text and disclaimers in all such redistributions of the Apple Software. |
Neither the name, trademarks, service marks or logos of Apple Inc. may |
be used to endorse or promote products derived from the Apple Software |
without specific prior written permission from Apple. Except as |
expressly stated in this notice, no other rights or licenses, express or |
implied, are granted by Apple herein, including but not limited to any |
patent rights that may be infringed by your derivative works or by other |
works in which the Apple Software may be incorporated. |
The Apple Software is provided by Apple on an "AS IS" basis. APPLE |
MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION |
THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS |
FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND |
OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS. |
IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL |
OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION, |
MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED |
AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE), |
STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE |
POSSIBILITY OF SUCH DAMAGE. |
Copyright (C) 2013 Apple Inc. All Rights Reserved. |
*/ |
#import "AccelerometerFilter.h" |
// Implementation of the basic filter. All it does is mirror input to output. |
@implementation AccelerometerFilter |
@synthesize x, y, z, adaptive; |
- (void)addAcceleration:(UIAcceleration *)accel |
{ |
x = accel.x; |
y = accel.y; |
z = accel.z; |
} |
- (NSString *)name |
{ |
return @"You should not see this"; |
} |
@end |
#pragma mark - |
#define kAccelerometerMinStep 0.02 |
#define kAccelerometerNoiseAttenuation 3.0 |
double Norm(double x, double y, double z) |
{ |
return sqrt(x * x + y * y + z * z); |
} |
double Clamp(double v, double min, double max) |
{ |
if(v > max) |
return max; |
else if(v < min) |
return min; |
else |
return v; |
} |
#pragma mark - |
// See http://en.wikipedia.org/wiki/Low-pass_filter for details low pass filtering |
@implementation LowpassFilter |
- (id)initWithSampleRate:(double)rate cutoffFrequency:(double)freq |
{ |
self = [super init]; |
if(self != nil) |
{ |
double dt = 1.0 / rate; |
double RC = 1.0 / freq; |
filterConstant = dt / (dt + RC); |
} |
return self; |
} |
- (void)addAcceleration:(UIAcceleration *)accel |
{ |
double alpha = filterConstant; |
if(adaptive) |
{ |
double d = Clamp(fabs(Norm(x, y, z) - Norm(accel.x, accel.y, accel.z)) / kAccelerometerMinStep - 1.0, 0.0, 1.0); |
alpha = (1.0 - d) * filterConstant / kAccelerometerNoiseAttenuation + d * filterConstant; |
} |
x = accel.x * alpha + x * (1.0 - alpha); |
y = accel.y * alpha + y * (1.0 - alpha); |
z = accel.z * alpha + z * (1.0 - alpha); |
} |
- (NSString *)name |
{ |
return adaptive ? @"Adaptive Lowpass Filter" : @"Lowpass Filter"; |
} |
@end |
#pragma mark - |
// See http://en.wikipedia.org/wiki/High-pass_filter for details on high pass filtering |
@implementation HighpassFilter |
- (id)initWithSampleRate:(double)rate cutoffFrequency:(double)freq |
{ |
self = [super init]; |
if (self != nil) |
{ |
double dt = 1.0 / rate; |
double RC = 1.0 / freq; |
filterConstant = RC / (dt + RC); |
} |
return self; |
} |
- (void)addAcceleration:(UIAcceleration *)accel |
{ |
double alpha = filterConstant; |
if (adaptive) |
{ |
double d = Clamp(fabs(Norm(x, y, z) - Norm(accel.x, accel.y, accel.z)) / kAccelerometerMinStep - 1.0, 0.0, 1.0); |
alpha = d * filterConstant / kAccelerometerNoiseAttenuation + (1.0 - d) * filterConstant; |
} |
x = alpha * (x + accel.x - lastX); |
y = alpha * (y + accel.y - lastY); |
z = alpha * (z + accel.z - lastZ); |
lastX = accel.x; |
lastY = accel.y; |
lastZ = accel.z; |
} |
- (NSString *)name |
{ |
return adaptive ? @"Adaptive Highpass Filter" : @"Highpass Filter"; |
} |
@end |
Copyright © 2013 Apple Inc. All Rights Reserved. Terms of Use | Privacy Policy | Updated: 2013-07-15