Question

您好我正在创建一个应用程序，它将使用Overlays在MapView顶部绘制线条。目前我已经设置了我想要使用projection.toPixel（）方法的GPS点。该方法不会抛出任何错误，但是当地图按原样移动时，点不会在地图上保持固定。有什么我想念的吗？

//Zoom into certain area
public boolean onKeyDown(int keyCode, KeyEvent event)
{ 
    MapController mc = mapView.getController();

    switch(keyCode)
    {
        case KeyEvent.KEYCODE_1:
            mc.zoomIn();
            break;

        case KeyEvent.KEYCODE_2:
            mc.zoomOut();
            break;

        case KeyEvent.KEYCODE_4:
            //Create new path
            path = new Path();

            //Get Location Data from GPS

            p = new GeoPoint(
                    (int) (54.9886454 * 1E6),
                    (int) (-7.522208 * 1E6));

            //Convert GPS location to Screen Pixels
            Point screenPts1 = new Point();

            mapView.getProjection().toPixels(p,  screenPts1);

            //Start Path and pass locations
            path.moveTo(screenPts1.x, screenPts1.y);
            path.lineTo(screenPts1.x, screenPts1.y);

            System.out.println("New Path ");
            break;  

        case KeyEvent.KEYCODE_5:                
            //Get Location Data from GPS

            p = new GeoPoint(
                    (int) (54.9984931 * 1E6),
                    (int) (-7.522208 * 1E6));

            //Convert GPS location to Screen Pixels
            Point screenPts2 = new Point();
            mapView.getProjection().toPixels(p,  screenPts2);

            //Pass locations to the path
            path.lineTo(screenPts2.x, screenPts2.y);

            System.out.println("Continue Path ");
            break;  

        case KeyEvent.KEYCODE_6:                
            //Get Location Data from GPS

            p = new GeoPoint(
                    (int) (54.9994777 * 1E6),
                    (int) (-7.5005787 * 1E6));

            //Convert GPS location to Screen Pixels
            Point screenPts3 = new Point();
            mapView.getProjection().toPixels(p, screenPts3);

            //Pass locations to the path
            path.lineTo(screenPts3.x, screenPts3.y);

            //Close the path and add it to the _graphics array for it to be drawn
            _graphics.add(path);

            System.out.println("End Path ");

            break;  
    }
    return super.onKeyDown(keyCode, event);
}

叠加类绘制方法：

public boolean draw(Canvas canvas, MapView mapView, boolean shadow,long when)
    {       
        super.draw(canvas,mapView,shadow);

        //-- Create new paint object --
        Paint mPaint = new Paint();
        mPaint.setDither(true);
        mPaint.setColor(Color.RED);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(2);

        //-- Take all the paths from the _graphics array and draw them to the Screen --
        for (Path path : _graphics) 
        {
            canvas.drawPath(path, mPaint);  
        }

        return true;
    }

Answer 1

从MapView.getProjection（）方法的文档：“地图在当前状态下的投影。你不应该坚持使用这个对象进行多次绘制，因为地图的投影可能会改变。”

因此，当您移动地图时，您必须重新计算像素位置，因为您计算前一个像素位置的投影不再有效，因此像素位置也不再有效。

如何通过叠加将GPS点转换为屏幕像素？

1 个答案: