Android将多边形从地图保存为所有设备的相同大小的位图

Question

I am drawing polygon on Google map and it works great. What I need is to save this polygon as bitmap for fixed scale. I am using this code to do that.

private static List<Point> scalePolygonPoints(List<LatLng> points, float scale, Projection projection) {
    List<Point> scaledPoints = new ArrayList(points.size());

    LatLng polygonCenter = getPolygonCenterPoint(points);
    Point centerPoint = projection.toScreenLocation(polygonCenter);

    for (int i=0; i < points.size(); i++) {
        Point screenPosition = projection.toScreenLocation(points.get(i));
        screenPosition.x = (int) (scale * (screenPosition.x - centerPoint.x) + centerPoint.x);
        screenPosition.y = (int) (scale * (screenPosition.y - centerPoint.y) + centerPoint.y);
        scaledPoints.add(screenPosition);
    }

    return scaledPoints;
}

private static LatLng getPolygonCenterPoint(List<LatLng> polygonPointsList){
    LatLng centerLatLng = null;
    LatLngBounds.Builder builder = new LatLngBounds.Builder();
    for(int i = 0; i < polygonPointsList.size() ; i++) {
        builder.include(polygonPointsList.get(i));
    }
    LatLngBounds bounds = builder.build();
    centerLatLng =  bounds.getCenter();
    return centerLatLng;
}

And then to create bitmap

private Bitmap createPolylineBitmap(List<Point> scaledPoints) {
            Bitmap bitmap = Bitmap.createBitmap(800, 600, Bitmap.Config.ARGB_8888);
            Canvas canvas = new Canvas(bitmap);

            Paint paint = new Paint();
            paint.setColor(ContextCompat.getColor(this, R.color.black));
            paint.setStrokeWidth(10);
            paint.setDither(true);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeJoin(Paint.Join.ROUND);
            paint.setStrokeCap(Paint.Cap.ROUND);
            paint.setAntiAlias(true);


            for (int i = 0; i < scaledPoints.size(); i++) {
                try {
                    canvas.drawLine(scaledPoints.get(i).x, scaledPoints.get(i).y, scaledPoints.get(i + 1).x, scaledPoints.get(i + 1).y, paint);
                }
                catch(Exception ex){
                    canvas.drawLine(scaledPoints.get(i).x, scaledPoints.get(i).y, scaledPoints.get(0).x, scaledPoints.get(0).y, paint);
                }
            }
            return bitmap;
        }

The problem is that this method uses screen projection and when user changes zoom or drags map it changes polygon position on bitmap or its even out of bounds. How can I make it to draw the same size polygon on all devices not depending on zoom, or camera position?

EDIT: So basically I managed to get the right size of polygon zooming map at right position before saving it to bitmap. But the problem is when I use device with different resoulution the polygon size is also changing. How to prevent that?

Answer 1

A clever hack that might work for you- why not manually zoom the camera to fit the polyline whenever user tries to save the geofence.

 val latLngs = getLatLngs()
 val builder = LatLngBounds.Builder()
 latLngs.forEach {
        builder.include(it.position)
 }
 val padding = 200
 val bounds = builder.build()
 val cameraUpdate = CameraUpdateFactory.newLatLngBounds(bounds, padding)
 map.moveCamera(cameraUpdate)
 //Do your projection operation here...

Answer 2

Save an svg image of your polygon. svg is vectoriel, bitmap is not