Merge pull request #489 from peterstace/bounding_diagonal

Add `BoundingDiagonal()` method to `Envelope`

CHANGELOG.md

@@ -5,6 +5,8 @@
 - Make `IgnoreOrder` a function rather than a global variable to prevent
   consumers from erroneously altering its behaviour.
 
+- Add a `BoundingDiagonal` method to the `Envelope` type.
+
 ## v0.41.0
 
 2022-11-15

geom/type_envelope.go

@@ -295,3 +295,27 @@ func (e Envelope) box() (rtree.Box, bool) {
 		MaxY: e.maxY,
 	}, !e.IsEmpty()
 }
+
+// BoundingDiagonal returns the LineString that goes from the point returned by
+// Min() to the point returned by Max(). If the envelope is degenerate and
+// represents a single point, then a Point is returned instead of a LineString.
+// If the Envelope is empty, then the empty Geometry (representing an empty
+// GeometryCollection) is returned.
+func (e Envelope) BoundingDiagonal() Geometry {
+	if e.IsEmpty() {
+		return Geometry{}
+	}
+	if e.IsPoint() {
+		return e.min().asUncheckedPoint().AsGeometry()
+	}
+
+	// The Envelope has already been validated, so it's safe to skip validation
+	// when constructing the diagonal.
+	coords := []float64{e.minX(), e.minY, e.maxX, e.maxY}
+	seq := NewSequence(coords, DimXY)
+	ls, err := NewLineString(seq, DisableAllValidations)
+	if err != nil {
+		panic("programming error: validations disabled by LineString validation failed")
+	}
+	return ls.AsGeometry()
+}

geom/type_envelope_test.go

@@ -582,3 +582,30 @@ func BenchmarkEnvelopeTransformXY(b *testing.B) {
 		expectNoErr(b, err)
 	}
 }
+
+func TestBoundingDiagonal(t *testing.T) {
+	for i, tc := range []struct {
+		env  []XY
+		want string
+	}{
+		{
+			nil,
+			"GEOMETRYCOLLECTION EMPTY",
+		},
+		{
+			[]XY{{1, 2}},
+			"POINT(1 2)",
+		},
+		{
+			[]XY{{3, 2}, {1, 4}},
+			"LINESTRING(1 2,3 4)",
+		},
+	} {
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			env, err := NewEnvelope(tc.env)
+			expectNoErr(t, err)
+			got := env.BoundingDiagonal()
+			expectGeomEqWKT(t, got, tc.want)
+		})
+	}
+}