--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pkg/imports/polygon.go	Thu Oct 18 12:22:08 2018 +0200
@@ -0,0 +1,78 @@
+package imports
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"math"
+
+	shp "github.com/jonas-p/go-shp"
+)
+
+type (
+	Point struct {
+		X float64
+		Y float64
+	}
+	LineString []Point
+	Polygon    []LineString
+)
+
+const (
+	wkbNDR     byte   = 1
+	wkbPolygon uint32 = 3
+)
+
+func shapeToPolygon(s shp.Shape) (Polygon, error) {
+	switch p := s.(type) {
+	case *shp.Polygon:
+		return toPolygon(p.NumParts, p.Parts, p.Points), nil
+	case *shp.PolygonZ:
+		return toPolygon(p.NumParts, p.Parts, p.Points), nil
+	case *shp.PolygonM:
+		return toPolygon(p.NumParts, p.Parts, p.Points), nil
+	}
+	return nil, fmt.Errorf("Unsupported shape type %T", s)
+}
+
+func toPolygon(numParts int32, parts []int32, points []shp.Point) Polygon {
+	out := make(Polygon, numParts)
+	pos := 0
+	for i := range out {
+		ps := parts[i]
+		line := make(LineString, ps)
+		for j := int32(0); j < ps; j, pos = j+1, pos+1 {
+			p := &points[pos]
+			line[j] = Point{p.X, p.Y}
+		}
+		out[i] = line
+	}
+	return out
+}
+
+func (p Polygon) AsWBK() []byte {
+	if p == nil {
+		return nil
+	}
+	// pre-calculate size to avoid reallocations.
+	size := 1 + 4 + 4
+	for _, ring := range p {
+		size += 4 + len(ring)*2*8
+	}
+
+	buf := bytes.NewBuffer(make([]byte, 0, size))
+
+	binary.Write(buf, binary.LittleEndian, wkbNDR)
+	binary.Write(buf, binary.LittleEndian, wkbPolygon)
+	binary.Write(buf, binary.LittleEndian, uint32(len(p)))
+
+	for _, ring := range p {
+		binary.Write(buf, binary.LittleEndian, uint32(len(ring)))
+		for _, v := range ring {
+			binary.Write(buf, binary.LittleEndian, math.Float64bits(v.X))
+			binary.Write(buf, binary.LittleEndian, math.Float64bits(v.Y))
+		}
+	}
+
+	return buf.Bytes()
+}