android - toPixels() 返回图 block 的像素，而不是屏幕

Question

我有一个使用 OSMDroid 显示 map 的 Android 应用程序。我想在屏幕上获取 GeoPoint 的投影像素，而不是在图 block 上。考虑以下代码:

Projection projection = getProjection();
GeoPoint geoPoint1 = (GeoPoint)projection.fromPixels(0, 0);  
Point pixelsPoint = new Point();
projection.toPixels(geoPoint1, pixelsPoint);
GeoPoint geoPoint2 = (GeoPoint)projection.fromPixels(pixelsPoint.x, pixelsPoint.y);

我希望 geoPoint1 等于 geoPoint2。相反，我得到 2 个完全不同的“GeoPoint”。在我看来，问题出在这一行:

projection.toPixels(geoPoint1, pixelsPoint);

out 变量 pixelsPoint 填充的值远高于屏幕尺寸(我得到 10,000+ x 和 y)，我怀疑这是图 block 上的像素，而不是屏幕像素。

如何从 GeoPoint 来回移动屏幕像素？

Answer 1

您需要补偿左上角的偏移量，这些方法应该有效:

/**
 * 
 * @param x  view coord relative to left
 * @param y  view coord relative to top
 * @param vw MapView
 * @return GeoPoint
 */

private GeoPoint geoPointFromScreenCoords(int x, int y, MapView vw){
    if (x < 0 || y < 0 || x > vw.getWidth() || y > vw.getHeight()){
        return null; // coord out of bounds
    }
    // Get the top left GeoPoint
    Projection projection = vw.getProjection();
    GeoPoint geoPointTopLeft = (GeoPoint) projection.fromPixels(0, 0);
    Point topLeftPoint = new Point();
    // Get the top left Point (includes osmdroid offsets)
    projection.toPixels(geoPointTopLeft, topLeftPoint);
    // get the GeoPoint of any point on screen 
    GeoPoint rtnGeoPoint = (GeoPoint) projection.fromPixels(x, y);
    return rtnGeoPoint;
}

/**
 * 
 * @param gp GeoPoint
 * @param vw Mapview
 * @return a 'Point' in screen coords relative to top left
 */

private Point pointFromGeoPoint(GeoPoint gp, MapView vw){

    Point rtnPoint = new Point();
    Projection projection = vw.getProjection();
    projection.toPixels(gp, rtnPoint);
    // Get the top left GeoPoint
    GeoPoint geoPointTopLeft = (GeoPoint) projection.fromPixels(0, 0);
    Point topLeftPoint = new Point();
    // Get the top left Point (includes osmdroid offsets)
    projection.toPixels(geoPointTopLeft, topLeftPoint);
    rtnPoint.x-= topLeftPoint.x; // remove offsets
    rtnPoint.y-= topLeftPoint.y;
    if (rtnPoint.x > vw.getWidth() || rtnPoint.y > vw.getHeight() || 
            rtnPoint.x < 0 || rtnPoint.y < 0){
        return null; // gp must be off the screen
    }
    return rtnPoint;
}