Question

I have created an off-line map with Google Map Android API v2 (i.e. osmdroid is not an option) using Openstreetmap tiles as GroundOverlays with one minor problem: at zoom level greater than 14 some of the tiles have a 1-3 pixel space between them. Other tiles line up perfectly. It seems random which ones do and do not have spaces between them.

I download the tiles using JTileDownloader, then I fetch the required tiles (using the technique described here) that I downloaded and placed in the device filesystem, then I get the tiles’ LatLngBounds, and then I lay them down in a loop as:

groundOverlay = mMap.addGroundOverlay(new GroundOverlayOptions()
                    .image(BitmapDescriptorFactory.fromBitmap(mBitmapImage))
                    .positionFromBounds(tileBoundsArray[i])
                    .transparency((float)0));

I have verified that the lat and long of the tiles should line up. I also verified that all the bitmaps are the same size. I have also tried this particular tileset using the UrlTileProvider and it works fine, so it’s nothing wrong with the tiles. I have been struggling with this for days and would appreciate any suggestions. I have found absolutely nothing anywhere else addressing this issue. Thanks!

Answer 1

I finally found the answer to this. I had to specify the width of the map tile in meters at the tile’s latitude (I used the center of the tile). Google maps uses a Mercator projection, which means that the width of the map depends upon the latitude. You specifiy the width using GoundOverlay.setDimensions(width). This page gives an explanation on how to calculate the width.