ArcGIS tile layer

[Mike]

I am trying to get the following map to work with route-me.

http://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/

It's put out by esri, and there seems to be some kind of math required inorder to get the tiles lined up properly. Does anyone know what calculations I need to perform on the zoom, x, y. 

[Mike]

NVM looks like the x and y just had to be flipped. 

        return [NSURL URLWithString:[NSString stringWithFormat:@"http://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/", tile.zoom, tile.y, tile.x]];

was all I needed.