Porting a Google Maps app to Osmdroid - problem with overlay

Question

I\'m porting a Google Maps based project to Osmdroid in order to use OpenStreetMaps. The port is working OK apart from adding my overlay which consists of a number of straig

Answer 1

I'm not sure where you are calling redrawOverlay() from, but if you look at the MinimapOverlay you will see an example where something is drawn at a fixed location on the screen. In other words, you are drawing in screen coordinates not in map coordinates.

Example:

@Override
protected void onDraw(final Canvas pC, final MapView pOsmv) {
  // Calculate the half-world size
  final Rect viewportRect = new Rect();
  final Projection projection = pOsmv.getProjection();
  final int zoomLevel = projection.getZoomLevel();
  final int tileZoom = projection.getTileMapZoom();
  mWorldSize_2 = 1 << (zoomLevel + tileZoom - 1);

  // Find what's on the screen
  final BoundingBoxE6 boundingBox = projection.getBoundingBox();
  final Point upperLeft = org.osmdroid.views.util.Mercator
            .projectGeoPoint(boundingBox.getLatNorthE6(), boundingBox.getLonWestE6(),
            zoomLevel + tileZoom, null);
  final Point lowerRight = org.osmdroid.views.util.Mercator
     .projectGeoPoint(boundingBox.getLatSouthE6(), boundingBox.getLonEastE6(), zoomLevel
     + tileZoom, null);

  // Save the Mercator coordinates of what is on the screen
  viewportRect.set(upperLeft.x, upperLeft.y, lowerRight.x, lowerRight.y);

  // Offset into OSM coordinates
  viewportRect.offset(-mWorldSize_2, -mWorldSize_2);

  // Draw a line from one corner to the other
  canvas.drawLine(viewportRect.left, viewportRect.top, viewportRect.right, viewportRect.bottom);

From here viewportRect represents the upper left to the lower right of the screen. You can use this to draw at any fixed points on the screen.

UPDATE:

To answer your second question - what you need to do is override onDoubleTap in your Overlay and return "true". Returning "true" indicates to the base class that you "consumed" the event and no further processing should take place. Take a look at the minimap overlay code for a good example:

http://code.google.com/p/osmdroid/source/browse/trunk/osmdroid-android/src/org/osmdroid/views/overlay/MinimapOverlay.java

We are right in the middle of overhauling the Overlays, so some of this will be handled a little better in the near future. For example, the getOverlays().clear() bug you ran into has also been reported elsewhere and we've since fixed it.