wip: cricle

vendor/github.com/tidwall/geojson/circle.go

@@ -1,7 +1,9 @@
 package geojson
 
 import (
+	"math"
 	"strconv"
+	"sync"
 
 	"github.com/tidwall/geojson/geo"
 	"github.com/tidwall/geojson/geometry"
@@ -210,12 +212,46 @@ func (g *Circle) getObject() Object {
 	return makeCircleObject(g.center, g.meters, g.steps)
 }
 
-func makeCircleObject(center geometry.Point, meters float64, steps int) Object {
+var llmu sync.RWMutex
+var llobj Object
+
+func makeCircleObjectA(center geometry.Point, meters float64, steps int) Object {
 	if meters <= 0 {
 		return NewPoint(center)
 	}
 	meters = geo.NormalizeDistance(meters)
-	var points []geometry.Point
+	points := make([]geometry.Point, 0, steps+1)
+
+	// calc the four corners
+	maxY, _ := geo.DestinationPoint(center.Y, center.X, meters, 0)
+	_, maxX := geo.DestinationPoint(center.Y, center.X, meters, 90)
+	minY, _ := geo.DestinationPoint(center.Y, center.X, meters, 180)
+	_, minX := geo.DestinationPoint(center.Y, center.X, meters, 270)
+	lons := (maxX - minX) / 2
+	lats := (maxY - minY) / 2
+
+	for th := 0.0; th <= 360.0; th += 360.0 / float64(steps) {
+		radians := (math.Pi / 180) * th
+		x := center.X + lats*math.Cos(radians)
+		y := center.Y + lons*math.Sin(radians)
+		points = append(points, geometry.Point{X: x, Y: y})
+	}
+	// add last connecting point, make a total of steps+1
+	points = append(points, points[0])
+
+	return NewPolygon(
+		geometry.NewPoly(points, nil, &geometry.IndexOptions{
+			Kind: geometry.None,
+		}),
+	)
+}
+func makeCircleObjectB(center geometry.Point, meters float64, steps int) Object {
+	if meters <= 0 {
+		return NewPoint(center)
+	}
+	meters = geo.NormalizeDistance(meters)
+	points := make([]geometry.Point, 0, steps+1)
+
 	step := 360.0 / float64(steps)
 	i := 0
 	for deg := 360.0; deg > 0; deg -= step {
@@ -223,11 +259,59 @@ func makeCircleObject(center geometry.Point, meters float64, steps int) Object {
 		points = append(points, geometry.Point{X: lon, Y: lat})
 		i++
 	}
+	// add last connecting point, make a total of steps+1
+	points = append(points, points[0])
+
+	return NewPolygon(
+		geometry.NewPoly(points, nil, &geometry.IndexOptions{
+			Kind: geometry.None,
+		}),
+	)
+}
+
+func makeCircleObject(center geometry.Point, meters float64, steps int) Object {
+	if meters <= 0 {
+		return NewPoint(center)
+	}
+
+	meters = geo.NormalizeDistance(meters)
+	points := make([]geometry.Point, 0, steps+1)
+	return makeCircleObjectA(center, meters, steps)
+
+	llmu.RLock()
+	if llobj != nil {
+		llmu.RUnlock()
+		return llobj
+	}
+	llmu.RUnlock()
+	llmu.Lock()
+	if llobj != nil {
+		llmu.Unlock()
+		return llobj
+	}
+	defer llmu.Unlock()
+
+	step := 360.0 / float64(steps)
+	i := 0
+	for deg := 360.0; deg > 0; deg -= step {
+		lat, lon := geo.DestinationPoint(center.Y, center.X, meters, deg)
+		points = append(points, geometry.Point{X: lon, Y: lat})
+		i++
+	}
+	// add last connecting point, make a total of steps+1
+	points = append(points, points[0])
+
+	// for i := 0; i < steps; i++ {
+	// 	fmt.Printf("%d: %v\n", i, points[i].X)
+	// }
+
 	// TODO: account for the pole and antimerdian. In most cases only a
 	// polygon is needed, but when the circle bounds passes the 90/180
 	// lines, we need to create a multipolygon
-	points = append(points, points[0])
-	return NewPolygon(
+
+	llobj = NewPolygon(
 		geometry.NewPoly(points, nil, geometry.DefaultIndexOptions),
 	)
+	// println(llobj.String())
+	return llobj
 }