缩放时的叠加行为

Question

我在使用叠加层时遇到问题。我在地图上绘制了一个多边形叠加层，但是，当我放大或缩小时，边缘不再与我想要的位置对齐。我该如何解决这个问题？

这是我启动应用程序时的样子（它完美地覆盖了整个停车场）： Correct

这是我缩小时的样子（边缘不再与停车场对齐。叠加层看起来比停车场大一点）： Zoomed out

此外，当我放大时，它并没有很好地对齐。在这种情况下，叠加层比停车场要小一些。 （抱歉，stackoverflow 不允许我发布超过 2 个链接）

关于如何解决此问题的任何建议？

代码如下：

private Projection projection; 
private List<Overlay> mapOverlays;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    MapView mapView = (MapView) findViewById(R.id.mapView); 
    mapView.setBuiltInZoomControls(true);

    MapController mc = mapView.getController();
    mc.setZoom(17); 
    mc.animateTo(new GeoPoint((int)(32.734248*1E6), (int)(-97.113448*1E6)));

    mapOverlays = mapView.getOverlays();        
    projection = mapView.getProjection();
    mapOverlays.add(new MyOverlay());        

    mapView.postInvalidate();
}

@Override
protected boolean isRouteDisplayed() {
    return false;
}

class MyOverlay extends Overlay{

    public MyOverlay(){

    }   

    public void draw(Canvas canvas, MapView mapv, boolean shadow){
        super.draw(canvas, mapv, shadow);

        Paint   mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setColor(Color.RED);
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setAlpha(100);

        GeoPoint gP1 = new GeoPoint(32733839,-97112976);
        GeoPoint gP2 = new GeoPoint(32733875, -97113448);
        GeoPoint gP3 = new GeoPoint(32734961,-97113455);
        GeoPoint gP4 = new GeoPoint(32734953, -97112962);

        Point p1 = new Point();
        Point p2 = new Point();
        Point p3 = new Point();
        Point p4 = new Point();
        Path path = new Path();

        projection.toPixels(gP1, p1);
        projection.toPixels(gP2, p2);
        projection.toPixels(gP3, p3);
        projection.toPixels(gP4, p4);

        path.moveTo(p1.x, p1.y);
        path.lineTo(p2.x,p2.y);
        path.lineTo(p3.x,p3.y);
        path.lineTo(p4.x,p4.y);

        canvas.drawPath(path, mPaint);
    }
}

}

Answer 1

每次缩放改变时，Projection 也会改变。即使您在地图中进行较大移动而不更改缩放比例，投影也可能会发生变化。

要更正您的代码，您需要添加如下行：

public void draw(Canvas canvas, MapView mapv, boolean shadow){ 
    super.draw(canvas, mapv, shadow); 

    Projection projection = mapv.getProjection();  //Add this line

    Paint   mPaint = new Paint(Paint.ANTI_ALIAS_FLAG); 
    mPaint.setColor(Color.RED); 
    mPaint.setStyle(Paint.Style.FILL); 
    mPaint.setAlpha(100); 

    GeoPoint gP1 = new GeoPoint(32733839,-97112976); 
    GeoPoint gP2 = new GeoPoint(32733875, -97113448); 
    GeoPoint gP3 = new GeoPoint(32734961,-97113455); 
    GeoPoint gP4 = new GeoPoint(32734953, -97112962); 

    Point p1 = new Point(); 
    Point p2 = new Point(); 
    Point p3 = new Point(); 
    Point p4 = new Point(); 
    Path path = new Path(); 

    projection.toPixels(gP1, p1); 
    projection.toPixels(gP2, p2); 
    projection.toPixels(gP3, p3); 
    projection.toPixels(gP4, p4); 

    path.moveTo(p1.x, p1.y); 
    path.lineTo(p2.x,p2.y); 
    path.lineTo(p3.x,p3.y); 
    path.lineTo(p4.x,p4.y); 

    canvas.drawPath(path, mPaint); 
} 

您可以删除在onCreate() 中创建的投影。

--已编辑--

改进 - 速战速决

onDraw() 每次移动地图或更改缩放级别时都会被调用两次，因此尽可能做到这一点很重要。您可以在下面找到一些建议：

private List<Overlay> mapOverlays; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    MapView mapView = (MapView) findViewById(R.id.mapView);  
    mapView.setBuiltInZoomControls(true); 

    MapController mc = mapView.getController(); 
    mc.setZoom(17);  
    mc.animateTo(new GeoPoint((int)(32.734248*1E6), (int)(-97.113448*1E6))); 

    mapOverlays = mapView.getOverlays();         
    mapOverlays.add(new MyOverlay());         

    mapView.postInvalidate(); 
} 

@Override 
protected boolean isRouteDisplayed() { 
    return false; 
} 

class MyOverlay extends Overlay{ 

    //Moved objects that need only one instance to the initialization, to avoid creating a new copy of each every time draw() runs  
    private Paint   mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

    private GeoPoint gP1 = new GeoPoint(32733839,-97112976); 
    private GeoPoint gP2 = new GeoPoint(32733875, -97113448); 
    private GeoPoint gP3 = new GeoPoint(32734961,-97113455); 
    private GeoPoint gP4 = new GeoPoint(32734953, -97112962); 

    private Point p1 = new Point(); 
    private Point p2 = new Point(); 
    private Point p3 = new Point(); 
    private Point p4 = new Point(); 
    private Path path = new Path(); 

    public MyOverlay(){
        //mPaint settings done on class creation, to avoid repeating them on draw() call 
        mPaint.setColor(Color.RED); 
        mPaint.setStyle(Paint.Style.FILL); 
        mPaint.setAlpha(100); 
    }    

    public void draw(Canvas canvas, MapView mapv, boolean shadow){ 
        super.draw(canvas, mapv, shadow); 

        //draw is always called twice, one with shadow equal to true and one to false.
        //This can be used to draw the same image with shadow
        //But you are not using shadows, so you can immediately return half of the calls, and reduce the draw() effort by half
        if(shadow) return;

        Projection projection = mapv.getProjection();

        projection.toPixels(gP1, p1); 
        projection.toPixels(gP2, p2); 
        projection.toPixels(gP3, p3); 
        projection.toPixels(gP4, p4); 

        path.rewind();
        path.moveTo(p1.x,p1.y); 
        path.lineTo(p2.x,p2.y); 
        path.lineTo(p3.x,p3.y); 
        path.lineTo(p4.x,p4.y); 

        canvas.drawPath(path, mPaint); 
    } 
} 

改进 - 更复杂的改进

我在下面描述的改进对于您当前的叠加层来说太过分了。只有当你有非常大的路径要绘制时才有意义。

当您在不缩放地图的情况下移动地图时，使用上面的代码，路径将被重新创建并在不同的位置重新绘制以与地图对齐。但是您创建的路径与之前的路径大小、形状相同，只是位置不同。

您可以使用以下方法获得相同的结果：

path.offset(dx, dy);

其中dx, dy 是移动路径以使其与地图对齐所需的像素数。当然，您需要跟踪上次偏移路径时地图在哪里，这样您就可以将路径偏移到新的地图位置。

如果您有一条包含数千个点的路径，则偏移该路径将比重新绘制它快 100 倍。

您还需要跟踪缩放级别，因为您仍然需要在缩放更改时重新创建路径。您不能使用getCurrentZoomLevel() 来执行此操作，因为它与缩放动画不同步。您需要测试longitudeSpan() 值的变化，以便能够与缩放变化动画同步创建路径。

我希望这会有所帮助。

问候。