tile38/geojson/bbox.go

package geojson

import (
	"bytes"
	"strconv"
	"math"

	"github.com/tidwall/tile38/geojson/poly"
)

// BBox is a bounding box
type BBox struct {
	Min Position
	Max Position
}

// New2DBBox creates a new bounding box
func New2DBBox(minX, minY, maxX, maxY float64) BBox {
	return BBox{Min: Position{X: minX, Y: minY, Z: 0}, Max: Position{X: maxX, Y: maxY, Z: 0}}
}

func fillBBox(m map[string]interface{}) (*BBox, error) {
	var bbox *BBox
	var ok bool
	switch v := m["bbox"].(type) {
	default:
		return nil, errBBoxInvalidType
	case nil:
	case []interface{}:
		if !(len(v) == 4 || len(v) == 6) {
			return nil, errBBoxInvalidNumberOfValues
		}
		bbox = &BBox{}
		if bbox.Min.X, ok = v[0].(float64); !ok {
			return nil, errBBoxInvalidValue
		}
		if bbox.Min.Y, ok = v[1].(float64); !ok {
			return nil, errBBoxInvalidValue
		}
		i := 2
		if len(v) == 6 {
			if bbox.Min.Z, ok = v[2].(float64); !ok {
				return nil, errBBoxInvalidValue
			}
			i = 3
		} else {
			bbox.Min.Z = nilz
		}
		if bbox.Max.X, ok = v[i+0].(float64); !ok {
			return nil, errBBoxInvalidValue
		}
		if bbox.Max.Y, ok = v[i+1].(float64); !ok {
			return nil, errBBoxInvalidValue
		}
		if len(v) == 6 {
			if bbox.Max.Z, ok = v[i+2].(float64); !ok {
				return nil, errBBoxInvalidValue
			}
		} else {
			bbox.Max.Z = nilz
		}
	}
	return bbox, nil
}

func (b *BBox) isCordZDefined() bool {
	return b != nil && (b.Min.Z != nilz || b.Max.Z != nilz)
}

func (b *BBox) write(buf *bytes.Buffer) {
	if b == nil {
		return
	}
	hasZ := b.Min.Z != nilz && b.Max.Z != nilz
	buf.WriteString(`,"bbox":[`)
	buf.WriteString(strconv.FormatFloat(b.Min.X, 'f', -1, 64))
	buf.WriteByte(',')
	buf.WriteString(strconv.FormatFloat(b.Min.Y, 'f', -1, 64))
	if hasZ {
		buf.WriteByte(',')
		buf.WriteString(strconv.FormatFloat(b.Min.Z, 'f', -1, 64))
	}
	buf.WriteByte(',')
	buf.WriteString(strconv.FormatFloat(b.Max.X, 'f', -1, 64))
	buf.WriteByte(',')
	buf.WriteString(strconv.FormatFloat(b.Max.Y, 'f', -1, 64))
	if hasZ {
		buf.WriteByte(',')
		buf.WriteString(strconv.FormatFloat(b.Max.Z, 'f', -1, 64))
	}
	buf.WriteByte(']')
}

func (b BBox) center() Position {
	return Position{
		(b.Max.X-b.Min.X)/2 + b.Min.X,
		(b.Max.Y-b.Min.Y)/2 + b.Min.Y,
		0,
	}
}

func (b BBox) union(bbox BBox) BBox {
	if bbox.Min.X < b.Min.X {
		b.Min.X = bbox.Min.X
	}
	if bbox.Min.Y < b.Min.Y {
		b.Min.Y = bbox.Min.Y
	}
	if bbox.Max.X > b.Max.X {
		b.Max.X = bbox.Max.X
	}
	if bbox.Max.Y > b.Max.Y {
		b.Max.Y = bbox.Max.Y
	}
	return b
}

func (b BBox) exterior() []Position {
	return []Position{
		{b.Min.X, b.Min.Y, 0},
		{b.Min.X, b.Max.Y, 0},
		{b.Max.X, b.Max.Y, 0},
		{b.Max.X, b.Min.Y, 0},
		{b.Min.X, b.Min.Y, 0},
	}
}

func rectBBox(bbox BBox) poly.Rect {
	return poly.Rect{
		Min: poly.Point{X: bbox.Min.X, Y: bbox.Min.Y, Z: 0},
		Max: poly.Point{X: bbox.Max.X, Y: bbox.Max.Y, Z: 0},
	}
}

// ExternalJSON is the simple json representation of the bounding box used for external applications.
func (b BBox) ExternalJSON() string {
	sw, ne := b.Min, b.Max
	sw.Z, ne.Z = 0, 0
	return `{"sw":` + sw.ExternalJSON() + `,"ne":` + ne.ExternalJSON() + `}`
}

// Sparse returns back an evenly distributed number of sub bboxs.
func (b BBox) Sparse(amount byte) []BBox {
	if amount == 0 {
		return []BBox{b}
	}
	var bboxes []BBox
	split := 1 << amount
	var xsize, ysize float64
	if b.Max.X < b.Min.X {
		// crosses the prime meridian
		xsize = (b.Min.X - b.Max.X) / float64(split)
	} else {
		xsize = (b.Max.X - b.Min.X) / float64(split)
	}
	if b.Max.Y < b.Min.Y {
		// crosses the equator
		ysize = (b.Min.Y - b.Max.Y) / float64(split)
	} else {
		ysize = (b.Max.Y - b.Min.Y) / float64(split)
	}

	for y := b.Min.Y; y < b.Max.Y; y += ysize {
		for x := b.Min.X; x < b.Max.X; x += xsize {
			bboxes = append(bboxes, BBox{
				Min: Position{X: x, Y: y, Z: b.Min.Z},
				Max: Position{X: x + xsize, Y: y + ysize, Z: b.Max.Z},
			})
		}
	}
	return bboxes
}

// BBoxesFromCenter calculates the bounding box surrounding a circle.
func BBoxesFromCenter(lat, lon, meters float64) (outer BBox) {

	outer.Min.Y, outer.Min.X, outer.Max.Y, outer.Max.X = BBoxBounds(lat, lon, meters)
	if outer.Min.X == outer.Max.X {
		switch outer.Min.X {
		case -180:
			outer.Max.X = 180
		case 180:
			outer.Min.X = -180
		}
	}

	return outer
}

func BBoxBounds(lat, lon, meters float64) (latMin, lonMin, latMax, lonMax float64) {

	// see http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates#Latitude
	lat = toRadians(lat)
	lon = toRadians(lon)

	r := meters / earthRadius // angular radius

	latMin = lat - r
	latMax = lat + r

	latT := math.Asin(math.Sin(lat) / math.Cos(r))
	lonΔ := math.Acos(( math.Cos(r) - math.Sin(latT) * math.Sin(lat)) / (math.Cos(latT) * math.Cos(lat) ))

	lonMin = lon - lonΔ
	lonMax = lon + lonΔ

	// Adjust for north poll
	if latMax > math.Pi/2 {
		lonMin = -math.Pi
		latMax = math.Pi/2
		lonMax = math.Pi
	}

	// Adjust for south poll
	if latMin < -math.Pi/2 {
		latMin = -math.Pi/2
		lonMin = -math.Pi
		lonMax = math.Pi
	}

	// Adjust for wraparound. Remove this if the commented-out condition below this block is added.
	if lonMin < -math.Pi || lonMax > math.Pi {
		lonMin = -math.Pi
		lonMax = math.Pi
	}

/*
	// Consider splitting area into two bboxes, using the below checks, and erasing above block for performance. See http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates#PolesAnd180thMeridian

	// Adjust for wraparound if minimum longitude is less than -180 degrees.
	if lonMin < -math.Pi {
// box 1:
		latMin = latMin
		latMax = latMax
		lonMin += 2*math.Pi
		lonMax = math.Pi
// box 2:
		latMin = latMin
		latMax = latMax
		lonMin = -math.Pi
		lonMax = lonMax
	}

	// Adjust for wraparound if minimum longitude is greater than -180 degrees.
	if lonMax > math.Pi {
// box 1:
		latMin = latMin
		latMax = latMax
		lonMin = lonMin
		lonMax = -math.Pi
// box 2:
		latMin = latMin
		latMax = latMax
		lonMin = -math.Pi
		lonMax -= 2*math.Pi
	}
*/

	lonMin = math.Mod(lonMin+3*math.Pi, 2*math.Pi) - math.Pi // normalise to -180..+180°
	lonMax = math.Mod(lonMax+3*math.Pi, 2*math.Pi) - math.Pi

	return toDegrees(latMin), toDegrees(lonMin), toDegrees(latMax), toDegrees(lonMax)
}