Reducing accelerometer sensor noise with Qt
(Makivioj -) |
(Makivioj -) |
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| Line 47: | Line 47: | ||
if (bufferPos < BUFFER_SIZE) { | if (bufferPos < BUFFER_SIZE) { | ||
readingBuffer->append(reading); | readingBuffer->append(reading); | ||
| − | bufferPos++; | + | bufferPos++; |
| + | return false; | ||
} | } | ||
else { | else { | ||
Revision as of 16:15, 4 July 2011
This code snippet shows how to reduce accelerometer noise using Qt.
Contents |
Introduction
In the CS000915 - Reducing accelerometer sensor noise code snippet, it was shown how to reduce accelerometer noise in Symbian/C++. This code snippet will show how this same noise filtering can be achieved using Qt.
Summary
Qt provides a possibility to add custom filters for QSensor objects. These filters can be used for decreasing the sensors notifying frequency. For the accelerometer a filter can be added by implementing the QAccelerometerFilter interface and adding it for the QAccelerometer object via the addFilter method. In this code snippet sixteen sensor readings are collected to a buffer and the average of these readings is set as the notified reading.
Preconditions
Qt 4.7 or higher is installed.
Sources
accelerometerfilter.h
#include <QAccelerometerFilter>
#include <QList>
QTM_USE_NAMESPACE
#define BUFFER_SIZE 16
class AccelerometerFilter : public QObject, public QAccelerometerFilter
{
Q_OBJECT
public:
explicit AccelerometerFilter(QObject *parent = 0);
private:
QList<QAccelerometerReading*> *readingBuffer;
int bufferPos;
public slots:
bool filter(QAccelerometerReading *reading);
accelerometerfilter.cpp
#include "accelerometerfilter.h"
AccelerometerFilter::AccelerometerFilter(QObject *parent) :
QAccelerometerFilter(), readingBuffer(new QList<QAccelerometerReading*>())
{
}
bool AccelerometerFilter::filter(QAccelerometerReading *reading)
{
if (bufferPos < BUFFER_SIZE) {
readingBuffer->append(reading);
bufferPos++;
return false;
}
else {
bufferPos = 0;
qreal xSum = 0, ySum = 0, zSum = 0;
for (int i = 0; i < readingBuffer->count(); i++) {
xSum += readingBuffer->at(i)->x();
ySum += readingBuffer->at(i)->y();
zSum += readingBuffer->at(i)->z();
}
readingBuffer->clear();
reading->setX(xSum / BUFFER_SIZE);
reading->setY(ySum / BUFFER_SIZE);
reading->setZ(zSum / BUFFER_SIZE);
return true;
}
}
myaccelerometer.h
#include <QAccelerometer>
#include <QVariant>
QTM_USE_NAMESPACE
class MyAccelerometer : public QObject {
Q_OBJECT
public:
explicit MyAccelerometer(QObject *parent = 0);
private:
QAccelerometer *accelerometer;
signals:
void accelerationChanged(QVariant, QVariant, QVariant);
public slots:
void updateAcceleration();
myaccelerometer.cpp
#include <QAccelerometerReading>
#include "myaccelerometer.h"
#include "accelerometerfilter.h"
MyAccelerometer::MyAccelerometer(QObject *parent) :
QObject(parent), accelerometer(new QAccelerometer(this)) {
accelerometer->addFilter(new AccelerometerFilter(this));
connect(accelerometer, SIGNAL(readingChanged()), this, SLOT(updateAcceleration()));
accelerometer->start();
}
void MyAccelerometer::updateAcceleration() {
QAccelerometerReading *reading = accelerometer->reading();
emit accelerationChanged(QVariant(reading->x()), QVariant(reading->y()), QVariant(reading->z()));
}
Postconditions
This code snippet demonstrated how to reduce accelerometer noise using Qt.
