function tileCornersWithCenter(z, x, y) {
  var top = tile2lat(y,z)
  var left = tile2long(x, z)
  var bottom = tile2lat(y+1, z)
  var right = tile2long(x+1, z)
  return [
    [left, bottom],
    [right, bottom],
    [right, top],
    [left, top],
    [(left + right)/2, (bottom + top)/2]
  ]
}
// get tile corner points and center
get tile corner points and center
get tile corner points and center
function tileCornersWithCenter(z, x, y) {
  var top = tile2lat(y,z)
  var left = tile2long(x, z)
  var bottom = tile2lat(y+1, z)
  var right = tile2long(x+1, z)
  return [
    [left, bottom],
    [right, bottom],
    [right, top],
    [left, top],
    [(left + right)/2, (bottom + top)/2]
  ]
}
function tileCornersWithCenter ( z , x , y ) { var top = tile2lat ( y , z ) var left = tile2long ( x , z ) var bottom = tile2lat ( y + 1 , z ) var right = tile2long ( x + 1 , z ) return [ [ left , bottom ] , [ right , bottom ] , [ right , top ] , [ left , top ] , [ ( left + right ) / 2 , ( bottom + top ) / 2 ] ] }
get tile corner points and center
get tile corner points and center