android - 像指南针一样旋转 ImageView(在别处设置 "north pole")

Question

我对如何实现“个人指南针”感到困惑，即指向特定方位而不是标准“北极”的指南针......不幸的是，我目前的尝试出现了错误(不是指向给定的方位角)。它还与加速器连接，能够根据用户转动的方式动态调整自身。

这是我目前的尝试(更新箭头的 onSensorChanged() 方法):

public void onSensorChanged( SensorEvent event ) {

            // If we don't have a Location, we break out
            if ( LocationObj == null ) return;

            float azimuth = event.values[0];
                            float baseAzimuth = azimuth;

            GeomagneticField geoField = new GeomagneticField( Double
                    .valueOf( LocationObj.getLatitude() ).floatValue(), Double
                    .valueOf( LocationObj.getLongitude() ).floatValue(),
                    Double.valueOf( LocationObj.getAltitude() ).floatValue(),
                    System.currentTimeMillis() );
            azimuth += geoField.getDeclination(); // converts magnetic north into true north

            //Correct the azimuth
            azimuth = azimuth % 360;

            //This is where we choose to point it
            float direction = azimuth + LocationObj.bearingTo( destinationObj );
            rotateImageView( arrow, R.drawable.arrow, direction );

            //Set the field
            if( baseAzimuth > 0 && baseAzimuth < 45 ) fieldBearing.setText("S");
            else if( baseAzimuth >= 45 && baseAzimuth < 90 ) fieldBearing.setText("SW");
            else if( baseAzimuth > 0 && baseAzimuth < 135 ) fieldBearing.setText("W");
            else if( baseAzimuth > 0 && baseAzimuth < 180 ) fieldBearing.setText("NW");
            else if( baseAzimuth > 0 && baseAzimuth < 225 ) fieldBearing.setText("N");
            else if( baseAzimuth > 0 && baseAzimuth < 270 ) fieldBearing.setText("NE");
            else if( baseAzimuth > 0 && baseAzimuth < 315 ) fieldBearing.setText("E");
            else if( baseAzimuth > 0 && baseAzimuth < 360 ) fieldBearing.setText("SE");
            else fieldBearing.setText("?"); 

        }

这是旋转 ImageView 的方法(rotateImageView()):

private void rotateImageView( ImageView imageView, int drawable, float rotate ) {

    // Decode the drawable into a bitmap
    Bitmap bitmapOrg = BitmapFactory.decodeResource( getResources(),
            drawable );

    // Get the width/height of the drawable
    DisplayMetrics dm = new DisplayMetrics(); getWindowManager().getDefaultDisplay().getMetrics(dm);
    int width = bitmapOrg.getWidth(), height = bitmapOrg.getHeight();

    // Initialize a new Matrix
    Matrix matrix = new Matrix();

    // Decide on how much to rotate
    rotate = rotate % 360;

    // Actually rotate the image
    matrix.postRotate( rotate, width, height );

    // recreate the new Bitmap via a couple conditions
    Bitmap rotatedBitmap = Bitmap.createBitmap( bitmapOrg, 0, 0, width, height, matrix, true );
    //BitmapDrawable bmd = new BitmapDrawable( rotatedBitmap );

    //imageView.setImageBitmap( rotatedBitmap );
    imageView.setImageDrawable(new BitmapDrawable(getResources(), rotatedBitmap));
    imageView.setScaleType( ScaleType.CENTER );
}

任何帮助将不胜感激，因为我不太知道如何进行。我在尝试时得到的“读数”有些不准确，并且指向错误的方向。我是在做一些真正的事情，还是我只是进行了一次非常糟糕的试运行？

Answer 1

您的 rotateImageView 函数应该可以正常工作，但是在您的旋转计算中需要更改一些内容。

//This is where we choose to point it
float direction = azimuth + LocationObj.bearingTo( destinationObj );
rotateImageView( arrow, R.drawable.arrow, direction );

问题是 BearingTo 会给你一个从 -180 到 180 的范围，这会让事情有点困惑。我们需要将此值转换为 0 到 360 的范围才能获得正确的旋转。

这是一张我们真正想要的表格，与bearingTo给我们的比较

+-----------+--------------+| bearingTo | Real bearing |+-----------+--------------+| 0         | 0            |+-----------+--------------+| 90        | 90           |+-----------+--------------+| 180       | 180          |+-----------+--------------+| -90       | 270          |+-----------+--------------+| -135      | 225          |+-----------+--------------+| -180      | 180          |+-----------+--------------+

Even though the bearingTo is in the range -180 to 180, 0 is still true north which will leave us to this calculation:

// Store the bearingTo in the bearTo variable
float bearTo = LocationObj.bearingTo( destinationObj );

// If the bearTo is smaller than 0, add 360 to get the rotation clockwise.
if (bearTo < 0) {
    bearTo = bearTo + 360;
}

如果我们添加一些虚拟值来测试我们的新公式:

float bearTo = -100;
// This will now equal to true
if (-100 < 0) {
    bearTo = -100 + 360 = 360 - 100 = 260;
}

我们现在已经解决了bearingTo，让我们继续前往方位角!

您需要减去偏角而不是相加，因为当我们将手机直接指向真北时，我们希望方位角为 0，而不是将偏角添加到方位角上，这样当我们将偏角加倍时将手机指向正北。通过减去偏角而不是添加偏角来纠正此问题。

azimuth -= geoField.getDeclination(); // converts magnetic north into true north

当我们现在将手机转向真北时，方位角将等于 0

您不再需要校正方位角的代码。

// Remove / uncomment this line
azimuth = azimuth % 360;

我们现在将继续计算实际旋转的位置。但首先我会总结一下我们现在拥有的值(value)观类型并解释它们的真正含义:

bearTo = 从我们当前所站的点，从真北到目标位置的角度。

azimuth = 您将手机从正北旋转的角度。

这样说，如果您将手机直接指向正北，我们真的希望箭头旋转 BearTo 设置的角度。如果您将手机指向正北 45 度，我们希望箭头比 BearTo 旋转 45 度。这让我们进行以下计算:

float direction = bearTo - azimuth;

但是，如果我们输入一些虚拟值: BearTo = 45; 方位角 = 180;

direction = 45 - 180 = -135;

这意味着箭头应该逆时针旋转 135 度。我们需要像使用 BearTo 一样放入一个类似的 if 条件!

// If the direction is smaller than 0, add 360 to get the rotation clockwise.
if (direction < 0) {
    direction = direction + 360;
}

您的轴承文本，N、E、S 和 W 已关闭，因此我已在下面的 final方法中更正它们。

您的 onSensorChanged 方法应如下所示:

public void onSensorChanged( SensorEvent event ) {

    // If we don't have a Location, we break out
    if ( LocationObj == null ) return;

    float azimuth = event.values[0];
    float baseAzimuth = azimuth;

    GeomagneticField geoField = new GeomagneticField( Double
        .valueOf( LocationObj.getLatitude() ).floatValue(), Double
        .valueOf( LocationObj.getLongitude() ).floatValue(),
        Double.valueOf( LocationObj.getAltitude() ).floatValue(),
        System.currentTimeMillis() );

    azimuth -= geoField.getDeclination(); // converts magnetic north into true north

    // Store the bearingTo in the bearTo variable
    float bearTo = LocationObj.bearingTo( destinationObj );

    // If the bearTo is smaller than 0, add 360 to get the rotation clockwise.
    if (bearTo < 0) {
        bearTo = bearTo + 360;
    }

    //This is where we choose to point it
    float direction = bearTo - azimuth;

    // If the direction is smaller than 0, add 360 to get the rotation clockwise.
    if (direction < 0) {
        direction = direction + 360;
    }

    rotateImageView( arrow, R.drawable.arrow, direction );

    //Set the field
    String bearingText = "N";

    if ( (360 >= baseAzimuth && baseAzimuth >= 337.5) || (0 <= baseAzimuth && baseAzimuth <= 22.5) ) bearingText = "N";
    else if (baseAzimuth > 22.5 && baseAzimuth < 67.5) bearingText = "NE";
    else if (baseAzimuth >= 67.5 && baseAzimuth <= 112.5) bearingText = "E";
    else if (baseAzimuth > 112.5 && baseAzimuth < 157.5) bearingText = "SE";
    else if (baseAzimuth >= 157.5 && baseAzimuth <= 202.5) bearingText = "S";
    else if (baseAzimuth > 202.5 && baseAzimuth < 247.5) bearingText = "SW";
    else if (baseAzimuth >= 247.5 && baseAzimuth <= 292.5) bearingText = "W";
    else if (baseAzimuth > 292.5 && baseAzimuth < 337.5) bearingText = "NW";
    else bearingText = "?";

    fieldBearing.setText(bearingText);

}