像指南针一样旋转 ImageView（在其他地方设置“北极”）

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，我当前的尝试结果是错误的（没有指向给定轴承）。它还与加速器连接，能够根据用户转动的方向动态调整自身。

这是我当前的尝试（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 );
}

任何帮助都会非常感谢，因为我不太知道如何继续。我在尝试时得到的“读数”有些不准确，并且指向错误的方向。我是否做了一些非常糟糕的事情，或者我只是进行了一次非常糟糕的测试？

Answer 1

您的rotateImageView 函数应该可以正常工作，但是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，这会让事情有点混乱。我们需要将此值转换为 0 到 360 的范围以获得正确的旋转。

这是我们真正想要的表格，与bearingTo给我们的内容进行比较

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

即使bearingTo在-180到180的范围内，0仍然是正北，这将让我们进行这个计算：

// 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;
}

我们现在已经整理出了方位角，让我们开始确定方位角！

您需要减去偏角而不是相加，因为当我们将手机直接指向正北时，我们希望方位角为 0，而不是将偏角添加到方位角上，这样当我们将手机指向正北时，方位角就会加倍到真正的北方。通过减去磁偏角（而不是加上磁偏角）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正北时，方位角将等于 0

您不再需要用于校正方位角的代码。

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

现在我们将继续计算实际旋转。但首先我将总结我们现在拥有的值类型并解释它们的真正含义：

bearTo = 从我们当前站立的点到目标位置的角度。

方位角 = 您将手机从正北方向旋转的角度。

也就是说，如果您将手机直接指向正北，我们确实希望箭头旋转 bearTo 设置的角度。如果您将手机指向与正北方向 45 度，我们希望箭头旋转的角度比 bearTo 的角度小 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：
熊托 = 45;
方位角=180；

direction = 45 - 180 = -135;

这意味着箭头应逆时针旋转 135 度。我们需要放入一个类似的 if 条件，就像我们对 bearTo 所做的那样！

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

您的方位文本、N、E、S 和 W 已关闭，因此我已在下面的最终方法中更正了它们。

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);

}

Answer 2

您应该能够将矩阵设置为 ImageView，而不必每次都重新创建位图，并且呃..“标准化”（是这个词吗？）读数。

float b = mLoc.getBearing();
if(b < 0)
    b = 360 + b;
float h = item.mHeading;
if(h < 0)
    h = 360 + h;
float r = (h - b) - 360;
matrix.reset();
matrix.postRotate(r, width/2, height/2);

在上面的示例中，mLoc 是 GPS 提供商返回的位置，而 getBearing 返回当前行进方向以东偏北的度数。 item.mHeading 是使用 Location.bearingTo() 函数（使用 mLoc 和项目的位置）计算得出的。宽度和高度是图像视图的尺寸。

因此，请确保您的变量以度数而不是弧度为单位，并尝试“标准化”（将航向设置在 0-360 的范围内，而不是 -180-180 的范围内）。另外，如果结果相差 180 度，请确保您获得的是目标的方位，而不是目标到您的度数。

然后可以在具有 ScaleType.Matrix 的 ImageView 中设置上面的矩阵，

imageView.setMatrix(matrix);
imageview.setScaleType(ScaleType.Matrix);

因为您围绕 imageView 的中心点旋转（postRotate 中的宽度/2、高度/2），所以您的可绘制对象应该指向上方并且将在绘制时旋转，而不是每次都重新创建新的位图。

Answer 3

一个周末我花了大约 40 个小时尝试做这件事。

屁股痛，希望我能减轻你的痛苦。

好吧，我警告你，这是一些丑陋的代码。
我很急于完成它，它没有命名方案，但我尽力为你做出最好的评论。

它被用来定位存放在田野中的大堆坚果。

使用手机当前的纬度和经度、目的地的纬度/经度、罗盘传感器和一些代数，我能够计算到目的地的方向。

纬度/经度和传感器读数是从 MainApplication 类中提取的。

这是 arrow.class 的一些代码，我用它在画布上向某个方向绘制箭头。

    //The location you want to go to//
    //"Given North"
    double lat=0;
    double lon=0;
    //////////////////////////////////
    protected void onDraw(Canvas canvas) {

    //Sensor values from another class managing Sensor
    float[] v = MainApplication.getValues();

    //The current location of the device, retrieved from another class managing GPS
    double ourlat=  MainApplication.getLatitudeD();
    double ourlon=  MainApplication.getLongitudeD(); 

    //Manually calculate the direction of the pile from the device
    double a= Math.abs((lon-ourlon));
    double b= Math.abs((lat-ourlat));
    //archtangent of a/b is equal to the angle of the device from 0-degrees in the first quadrant. (Think of a unit circle)
    double thetaprime= Math.atan(a/b);
    double theta= 0;

    //Determine the 'quadrant' that the desired location is in
    //ASTC (All, Sin, Tan, Cos)  Determines which value is positive
    //Gotta love Highschool algebra

    if((lat<ourlat)&&(lon>ourlon)){//-+ 
        //theta is 180-thetaprime because it is in the 2nd quadrant
        theta= ((Math.PI)-thetaprime); 

        //subtract theta from the compass value retrieved from the sensor to get our final direction
        theta=theta - Math.toRadians(v[0]);

    }else if((lat<ourlat)&&(lon<ourlon)){//--
        //Add 180 degrees because it is in the third quadrant
        theta= ((Math.PI)+thetaprime);

        //subtract theta from the compass value retreived from the sensor to get our final direction
        theta=theta - Math.toRadians(v[0]);

    }else if((lat>ourlat)&&(lon>ourlon)){ //++
        //No change is needed in the first quadrant
        theta= thetaprime; 

        //subtract theta from the compass value retreived from the sensor to get our final direction
        theta=theta - Math.toRadians(v[0]);

    }else if((lat>ourlat)&&(lon<ourlon)){ //+-
        //Subtract thetaprime from 360 in the fourth quadrant
        theta= ((Math.PI*2)-thetaprime);

        //subtract theta from the compass value retreived from the sensor to get our final direction
        theta=theta - Math.toRadians(v[0]);

    }

    canvas.drawBitmap(_bitmap, 0, 0, paint);
    float[] results = {0}; //Store data
    Location.distanceBetween(ourlat, ourlon, lat, lon, results);
    try{

        //Note, pileboundary is a value retreived from a database
        //This changes the color of the canvas based upon how close you are to the destination
        //Green < 100 (or database value), Yellow < (100)*2, Otherwise red
        if((results[0])<(pileboundary==0?100:pileboundary)){
            _canvas.drawColor(Color.GREEN);
        }else if((results[0])<(pileboundary==0?100:pileboundary)*2){
            _canvas.drawColor(Color.YELLOW);
        }else{
            _canvas.drawColor(Color.rgb(0xff, 113, 116)); //RED-ish
        }
        //Draw the distance(in feet) from the destination
        canvas.drawText("Distance: "+Integer.toString((int) (results[0]*3.2808399))+ " Feet", 3, height-3, textpaint);
    }catch(IllegalArgumentException ex){
        //im a sloppy coder 
    }
    int w = canvas.getWidth();
    int h = height;
    int x = w / 2; //put arrow in center
    int y = h / 2;
    canvas.translate(x, y);
    if (v != null) {

         // Finally, we rotate the canvas to the desired direction
         canvas.rotate((float)Math.toDegrees(theta));


    }
    //Draw the arrow!
    canvas.drawPath(thearrow, paint);
}   


//Some of my declarations, once again sorry :P
GeomagneticField gf;
Bitmap _bitmap;
Canvas _canvas;
int _height;
int _width; 
Bitmap b;
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    //Get the current GeomagneticField (Should be valid until 2016, according to android docs)
    gf = new GeomagneticField((float)lat,(float)lon,(float)MainApplication.getAltitude(),System.currentTimeMillis());
    _height = View.MeasureSpec.getSize(heightMeasureSpec);
    _width = View.MeasureSpec.getSize(widthMeasureSpec);
    setMeasuredDimension(_width, _height);
    _bitmap = Bitmap.createBitmap(_width, _height, Bitmap.Config.ARGB_8888);
    _canvas = new Canvas(_bitmap);
    b=Bitmap.createBitmap(_bitmap);
    drawBoard();
    invalidate();
}


//Here is the code to draw the arrow 
    thearrow.moveTo(0, -50);
    thearrow.lineTo(-20, 50);
    thearrow.lineTo(0, 50);
    thearrow.lineTo(20, 50);
    thearrow.close();
    thearrow.setFillType(FillType.EVEN_ODD);

希望你能读懂我的代码...如果我有时间，我会把它做得更漂亮一点。

如果您需要任何解释，请告诉我。

-桑德尔先生