some refinement and beginning of a table element

common/geo/point.go

@@ -0,0 +1,19 @@
+package geo
+
+type Point struct {
+	X, Y int
+}
+
+func (p Point) Delta(p2 Point) Point {
+	return Point{
+		X: p2.X - p.X,
+		Y: p2.Y - p.Y,
+	}
+}
+
+func (p Point) Add(p2 Point) Point {
+	return Point{
+		X: p.X + p2.X,
+		Y: p.Y + p2.Y,
+	}
+}