Merge pull request #402 from PDOK/pad-linestring-bbox

fix(transform): pad bbox for linestrings with 0 bbox area

Author: kad-korpem

internal/engine/util/bbox.go

@@ -22,3 +22,18 @@ func EncodeBBox(bbox geom.T) (*[]float64, error) {
 		return nil, fmt.Errorf("unsupported type: %d", rune(l))
 	}
 }
+
+// For linestrings specifically, it is possible for the min and max values of a dimension
+// to be exactly equal, resulting in a bbox with 0 area. This function pads the max value
+// of the relevant dimension by 1 unit to avoid this.
+// Returns the original bbox if neither dimension has equal min and max values.
+func PadBbox(bbox *geom.Bounds) *geom.Bounds {
+	if bbox.Max(0) == bbox.Min(0) {
+		// pad bbox.Max(0)
+		return geom.NewBounds(geom.XY).Set(bbox.Min(0), bbox.Min(1), bbox.Max(0)+1, bbox.Max(1))
+	} else if bbox.Max(1) == bbox.Min(1) {
+		// pad bbox.Max(1)
+		return geom.NewBounds(geom.XY).Set(bbox.Min(0), bbox.Min(1), bbox.Max(0), bbox.Max(1)+1)
+	}
+	return bbox
+}

internal/engine/util/bbox_test.go

@@ -95,3 +95,51 @@ func TestEncodeBBox(t *testing.T) {
 		})
 	}
 }
+
+func TestPadBbox(t *testing.T) {
+	type args struct {
+		bbox *geom.Bounds
+	}
+	type want struct {
+		bbox *geom.Bounds
+	}
+	tests := []struct {
+		name string
+		args args
+		want want
+	}{
+		{
+			name: "Vertical line bbox (X padding)",
+			args: args{
+				bbox: geom.NewBounds(geom.XY).Set(1, 1, 1, 2),
+			},
+			want: want{
+				bbox: geom.NewBounds(geom.XY).Set(1, 1, 2, 2),
+			},
+		},
+		{
+			name: "Horizontal line bbox (Y padding)",
+			args: args{
+				bbox: geom.NewBounds(geom.XY).Set(1, 1, 2, 1),
+			},
+			want: want{
+				bbox: geom.NewBounds(geom.XY).Set(1, 1, 2, 2),
+			},
+		},
+		{
+			name: "Diagonal line bbox (no padding)",
+			args: args{
+				bbox: geom.NewBounds(geom.XY).Set(1, 1, 2, 2),
+			},
+			want: want{
+				bbox: geom.NewBounds(geom.XY).Set(1, 1, 2, 2),
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := PadBbox(tt.args.bbox)
+			assert.Equal(t, tt.want.bbox, got)
+		})
+	}
+}

internal/ogc/features_search/etl/transform/transform.go

@@ -124,6 +124,9 @@ func (r RawRecord) transformBbox() (*geom.Polygon, error) {
 	if strings.EqualFold(r.GeometryType, "POINT") {
 		return nil, nil // No bbox for point geometries
 	}
+	if strings.EqualFold(r.GeometryType, "LINESTRING") {
+		r.Bbox = util.PadBbox(r.Bbox) // Slightly pad bbox for exact north-south or east-west linestrings to avoid 0 area
+	}
 	if util.SurfaceArea(r.Bbox) <= 0 {
 		return nil, errors.New("bbox area must be greater than zero")
 	}