无法解析符号“Lowpassfilter”

Question

我一直在使用http://www.ssaurel.com/blog/learn-how-to-make-a-compass-application-for-android/网站上的指南针代码。实际上，我是一个新开发的指南针应用程序，我得到了一个错误，无法解析符号'LowPassFilter‘。我已经导入了所有可能的文件，但仍然存在相同的错误

@Override
 public void onSensorChanged(SensorEvent event) {
  boolean accelOrMagnetic = false;

// get accelerometer data
if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
  // we need to use a low pass filter to make data smoothed
  smoothed = **LowPassFilter**.filter(event.values, gravity);
  gravity[0] = smoothed[0];
  gravity[1] = smoothed[1];
  gravity[2] = smoothed[2];
  accelOrMagnetic = true;

} else if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD) {
  smoothed = **LowPassFilter**.filter(event.values, geomagnetic);
  geomagnetic[0] = smoothed[0];
  geomagnetic[1] = smoothed[1];
  geomagnetic[2] = smoothed[2];
  accelOrMagnetic = true;

}

// get rotation matrix to get gravity and magnetic data
SensorManager.getRotationMatrix(rotation, null, gravity, geomagnetic);
// get bearing to target
SensorManager.getOrientation(rotation, orientation);
 // east degrees of true North
 bearing = orientation[0];
 // convert from radians to degrees
 bearing = Math.toDegrees(bearing);

 // fix difference between true North and magnetical North
 if (geomagneticField != null) {
 bearing += geomagneticField.getDeclination();
 }

 // bearing must be in 0-360
 if (bearing < 0) {
  bearing += 360;
 }

 // update compass view
 compassView.setBearing((float) bearing);

 if (accelOrMagnetic) {
  compassView.postInvalidate();
 }

updateTextDirection(bearing); // display text direction on screen function
}

Answer 1

我在http://www.java2s.com/Open-Source/Android_Free_Code/Sensor/compass/com_jwetherell_compass_commonLowPassFilter_java.htm上找到了答案。

package com.jwetherell.compass.common;
/* w  w  w  . j  a v a  2 s  .co m*/
/**
 * This class implements a low-pass filter. A low-pass filter is an electronic
 * filter that passes low-frequency signals but attenuates (reduces the
 * amplitude of) signals with frequencies higher than the cutoff frequency. The
 * actual amount of attenuation for each frequency varies from filter to filter.
 * It is sometimes called a high-cut filter, or treble cut filter when used in
 * audio applications.
 * 
 * @author Justin Wetherell (phishman3579@gmail.com)
 */
public class LowPassFilter {

    /*
     * Time smoothing constant for low-pass filter 0 ? ? ? 1 ; a smaller value
     * basically means more smoothing See:
     * http://en.wikipedia.org/wiki/Low-pass_filter#Discrete-time_realization
     */
    private static final float ALPHA = 0.2f;

    private LowPassFilter() {
    }

    /**
     * Filter the given input against the previous values and return a low-pass
     * filtered result.
     * 
     * @param input
     *            float array to smooth.
     * @param prev
     *            float array representing the previous values.
     * @return float array smoothed with a low-pass filter.
     */
    public static float[] filter(float[] input, float[] prev) {
        if (input == null || prev == null) throw new NullPointerException("input and prev float arrays must be non-NULL");
        if (input.length != prev.length) throw new IllegalArgumentException("input and prev must be the same length");

        for (int i = 0; i < input.length; i++) {
            prev[i] = prev[i] + ALPHA * (input[i] - prev[i]);
        }
        return prev;
    }
}