code: func (t T) Circle(center kml.Coordinate, radius, maxErr float64) []kml.Coordinate {
  	numVertices := int(math.Ceil(math.Pi / math.Acos((radius-maxErr)/(radius+maxErr))))
  	cs := make([]kml.Coordinate, numVertices+1)
  	for i := 0; i < numVertices; i++ {
  		cs[i] = t.Offset(center, radius, 360*float64(i)/float64(numVertices))
  	}
  	cs[numVertices] = cs[0]
  	return cs
  }
docs: // Circle returns an array of kml.Coordinates that approximate a circle of
  // radius radius centered on center with a maximum error of maxErr.