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polygon.go
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polygon.go
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package geo
import (
"database/sql/driver"
"encoding/json"
"fmt"
"strings"
)
const (
polygonWKTPrefix = `POLYGON(`
polygonWKTSuffix = `)`
)
var (
polygonJSONPrefix = []byte(`{"type":"Polygon","coordinates":[`)
polygonJSONSuffix = []byte(`]}`)
)
// Polygon is a GeoJSON Polygon.
type Polygon [][][3]float64
// Equal compares one polygon to another.
func (polygon Polygon) Equal(g Geometry) bool {
p, ok := g.(*Polygon)
if !ok {
return false
}
if len(polygon) != len(*p) {
return false
}
for i, p1 := range polygon {
p2 := (*p)[i]
if len(p1) != len(p2) {
return false
}
if !pointsEqual(p1, p2) {
return false
}
}
return true
}
// Contains uses the ray casting algorithm to decide
// if the point is contained in the polygon.
func (polygon Polygon) Contains(point Point) bool {
intersections := 0
for _, poly := range polygon {
for j, vertex := range poly {
if point.RayhIntersects(poly[(j+1)%len(poly)], vertex) {
intersections++
}
}
}
return (intersections % 2) == 1
}
// MarshalJSON returns the GeoJSON representation of the polygon.
func (polygon Polygon) MarshalJSON() ([]byte, error) {
s := polygonJSONPrefix
for i, poly := range polygon {
if i == 0 {
s = append(s, '[')
} else {
s = append(s, ',', '[')
}
s = append(s, pointsMarshalJSON(poly, "", "")...)
s = append(s, ']')
}
return append(s, polygonJSONSuffix...), nil
}
// Scan scans a polygon from Well Known Text.
func (polygon *Polygon) Scan(src interface{}) error {
return scan(polygon, src)
}
// scan scans a polygon from a Well Known Text string.
func (polygon *Polygon) scan(s string) error {
if i := strings.Index(s, polygonWKTPrefix); i != 0 {
return fmt.Errorf("malformed polygon %s", s)
}
l := len(s)
if s[l-len(polygonWKTSuffix):] != polygonWKTSuffix {
return fmt.Errorf("malformed polygon %s", s)
}
s = s[len(polygonWKTPrefix) : l-len(polygonWKTSuffix)]
// empty the polygon
*polygon = Polygon{}
// get the coordinates
polygons := strings.Split(s, "),(")
for _, ss := range polygons {
points, err := pointsScan(ss)
if err != nil {
return err
}
*polygon = append(*polygon, points)
}
return nil
}
// String converts the polygon to a string.
func (polygon Polygon) String() string {
if len(polygon) == 0 {
return "POLYGON EMPTY"
}
s := polygonWKTPrefix
for i, points := range polygon {
if i == 0 {
s += pointsString(points)
} else {
s += "," + pointsString(points)
}
}
return s + polygonWKTSuffix
}
// UnmarshalJSON unmarshals the polygon from GeoJSON.
func (polygon *Polygon) UnmarshalJSON(data []byte) error {
g := &geometry{}
// Never fails since data is always valid JSON.
_ = json.Unmarshal(data, g)
if expected, got := PolygonType, g.Type; expected != got {
return fmt.Errorf("expected type %s, got %s", expected, got)
}
p := [][][3]float64{}
if err := json.Unmarshal(g.Coordinates, &p); err != nil {
return err
}
*polygon = Polygon(p)
return nil
}
// Value converts a point to Well Known Text.
func (polygon Polygon) Value() (driver.Value, error) {
return polygon.String(), nil
}
// Transform transforms the geometry point by point.
func (polygon *Polygon) Transform(t Transformer) {
np := make([][][3]float64, len(*polygon))
for i, line := range *polygon {
nl := make([][3]float64, len(line))
for j, point := range line {
nl[j] = t.Transform(point)
}
np[i] = nl
}
*polygon = np
}
// VisitCoordinates visits each point in the geometry.
func (polygon Polygon) VisitCoordinates(v Visitor) {
for _, line := range polygon {
for _, point := range line {
v.Visit(point)
}
}
}