'Projected rendering envelope (xmin, ymin, xmax, ymax) for a metatile.'

def metaEnvelope(self, coord):

    buffer = (float(self.metatile.buffer) / self.dim)
    coords = self.metatile.allCoords(coord)
    ul = coords[0].left(buffer).up(buffer)
    lr = coords[(-1)].right((1 + buffer)).down((1 + buffer))
    ul = self.projection.coordinateProj(ul)
    lr = self.projection.coordinateProj(lr)
    return (min(ul.x, lr.x), min(ul.y, lr.y), max(ul.x, lr.x), max(ul.y, lr.y))
