package border

import (
        "image"
        "strings"

        log "github.com/sirupsen/logrus"
)

const (
        Outer = 0
        Hole  = 1
)

// Contour represents a single contour/border extracted from an image.
// It also tracks its parents and children.
type Contour struct {

        // Points making up the contour
        Points []image.Point

        Id int

        // Outer or Hole.
        BorderType int

        // Id of parent
        ParentId int

        // ParentCollision indicates if colliding with parent. Just an optimisation for quick removal later on.
        ParentCollision bool

        // Parent links to contours parent
        Parent *Contour

        // Children links to contours children
        Children []*Contour

        // ConflictingContours is a map of contours that we KNOW we conflict with. This may be the parent or other
        // siblings
        ConflictingContours map[int]bool // hate to use maps here... but want uniqueness

        // usable or not. Not filtering out but marking that we may not use it. (say if we're conflicting with another contour)
        Usable bool
}

// NewContour create new contour
func NewContour(id int) *Contour {
        c := Contour{}
        c.Id = id
        c.BorderType = Hole
        c.ConflictingContours = make(map[int]bool)
        c.Usable = true
        return &c
}

// GetAllPoints returns all points in the contour and all children.
func (c *Contour) GetAllPoints() []image.Point {

        var allPoints []image.Point

        for _, p := range c.Points {
                allPoints = append(allPoints, p)
        }

        for _, ch := range c.Children {
                points := ch.GetAllPoints()
                allPoints = append(allPoints, points...)
        }

        return allPoints
}

// ContourStats generates writes the stats to a log about the contour and all children.
// Primarily used for debugging
func ContourStats(c *Contour, offset int) {
        if len(c.Points) > 0 {
                pad := strings.Repeat(" ", offset)
                log.Debugf("%s%d : len %d :  no kids %d : no col %d : col with parent %+v\n", pad, c.Id, len(c.Points), len(c.Children), len(c.ConflictingContours), c.ParentCollision)
        }

        for _, ch := range c.Children {
                ContourStats(ch, offset+2)
        }
}

// ContourStatsWithCollisions generates writes to stdout stats about the contour and all children that have collisions
// Primarily used for debugging.
func ContourStatsWithCollisions(c *Contour, offset int) {
        if len(c.Points) > 0 {
                if len(c.ConflictingContours) > 0 {
                        pad := strings.Repeat(" ", offset)
                        log.Debugf("%s%d : len %d :  no kids %d : no col %d : col with parent %+v\n", pad, c.Id, len(c.Points), len(c.Children), len(c.ConflictingContours), c.ParentCollision)
                }
        }

        for _, ch := range c.Children {
                ContourStatsWithCollisions(ch, offset+2)
        }
}

package border

import (
        "errors"
        "image"

        "github.com/kpfaulkner/borders/common"
        log "github.com/sirupsen/logrus"
)

var (

        // dirDelta determines which direction will we move based on the direction (0-7) index
        dirDelta = []image.Point{{0, -1}, {1, -1}, {1, 0}, {1, 1}, {0, 1}, {-1, 1}, {-1, 0}, {-1, -1}}
)

// clockwise determines direction if we have 'dir' and turn clockwise
func clockwise(dir int) int {
        return (dir + 1) % 8
}

// counterClockwise determines direction if we have 'dir' and turn counterclockwise
func counterClockwise(dir int) int {
        return (dir + 7) % 8
}

// move moves the current point (pixel) in the direction 'dir'
func move(pixel image.Point, img *common.SuzukiImage, dir int) image.Point {
        newP := pixel.Add(dirDelta[dir])
        width := img.Width
        height := img.Height

        if (0 < newP.Y && newP.Y < height) && (0 < newP.X && newP.X < width) {
                if img.Get(newP) != 0 {
                        return newP
                }
        }
        return image.Point{0, 0}
}

// calcDir returns index of dirDelta that matches direction taken.
func calcDir(from image.Point, to image.Point) (int, error) {
        delta := to.Sub(from)
        for i, d := range dirDelta {
                if d.X == delta.X && d.Y == delta.Y {
                        return i, nil
                }
        }

        return 0, errors.New("unable to determine direction")
}

// createBorder returns the slice of Points making up the border/contour
// Also returns list of nbd's that are colliding with this. Can use to help create
// tree with collision info later.
func createBorder(img *common.SuzukiImage, p0 image.Point, p2 image.Point, nbd int, done []bool) ([]image.Point, map[int]bool, error) {

        // track which borders have conflicts
        collisionIndicies := make(map[int]bool)

        border := []image.Point{}
        dir, err := calcDir(p0, p2)
        if err != nil {
                log.Errorf("unable to determine direction: %s", err.Error())
                return nil, nil, err
        }

        moved := clockwise(dir)
        p1 := image.Point{0, 0}
        for moved != dir {
                newP := move(p0, img, moved)
                if newP.Y != 0 {
                        p1 = newP
                        break
                }
                moved = clockwise(moved)
        }

        if p1.X == 0 && p1.Y == 0 {
                return []image.Point{}, collisionIndicies, nil
        }
        p2 = p1
        p3 := p0

        for {
                dir, err = calcDir(p3, p2)
                if err != nil {
                        log.Errorf("unable to determine direction: %s", err.Error())
                        return nil, nil, err
                }
                moved = counterClockwise(dir)
                p4 := image.Point{0, 0}
                done = []bool{false, false, false, false, false, false, false, false}
                for {
                        p4 = move(p3, img, moved)
                        if p4.Y != 0 {
                                break
                        }
                        done[moved] = true
                        moved = counterClockwise(moved)
                }

                // detect if colliding with something else (ie not 0 nor 1)
                curP3 := img.Get(p3)
                if curP3 != 1 {
                        if curP3 < 0 {
                                curP3 *= -1
                        }

                        absNbd := nbd
                        if absNbd < 0 {
                                absNbd *= -1
                        }
                        collisionIndicies[curP3] = true
                        collisionIndicies[absNbd] = true
                }

                border = append(border, p3)
                if p3.Y == img.Height-1 || done[2] {
                        img.Set(p3, -1*nbd)
                } else if img.Get(p3) == 1 {
                        img.Set(p3, nbd)
                }

                if p4.X == p0.X && p4.Y == p0.Y && p3.X == p1.X && p3.Y == p1.Y {
                        break
                }

                p2 = p3
                p3 = p4
        }

        return border, collisionIndicies, nil
}

// addCollisionFlag mark contours with collisions with other contours.
func addCollisionFlag(contour *Contour, parentId int, contours map[int]*Contour, collisionIndices map[int]bool) {
        for contour1 := range collisionIndices {

                // quick indicator to say colliding with parent.
                if contour1 == parentId {
                        contour.ParentCollision = true
                }

                for contour2 := range collisionIndices {
                        if contour1 != contour2 {
                                c1 := contours[contour1]
                                c1.ConflictingContours[contour2] = true
                        }
                }
        }
}

// FindContours takes a SuzukiImage and determines the Contours that are present.
// It returns the single parent contour which in turn has all other contours as children or further
// generations.
func FindContours(img *common.SuzukiImage) (*Contour, error) {
        nbd := 1
        lnbd := 1

        contours := make(map[int]*Contour)
        done := []bool{false, false, false, false, false, false, false, false}

        contour := NewContour(1)
        contours[lnbd] = contour

        height := img.Height
        width := img.Width

        for i := 0; i < height; i++ {
                lnbd = 1
                for j := 0; j < width; j++ {
                        fji := img.GetXY(j, i)
                        isOuter := fji == 1 && (j == 0 || img.GetXY(j-1, i) == 0)
                        isHole := fji >= 1 && (j == width-1 || img.GetXY(j+1, i) == 0)
                        if isOuter || isHole {

                                var contourPrime *Contour
                                contour := NewContour(1)
                                from := image.Point{j, i}
                                parentId := 0
                                if isOuter {
                                        nbd += 1
                                        from = from.Sub(image.Point{1, 0})
                                        contour.BorderType = Outer
                                        contourPrime = contours[lnbd]
                                        if contourPrime.BorderType == Outer {
                                                parentId = contourPrime.ParentId
                                        } else {
                                                parentId = contourPrime.Id
                                        }
                                } else {
                                        nbd += 1
                                        if fji > 1 {
                                                lnbd = fji
                                        }
                                        contourPrime = contours[lnbd]
                                        from = from.Add(image.Point{1, 0})
                                        contour.BorderType = Hole
                                        if contourPrime.BorderType == Outer {
                                                parentId = contourPrime.Id
                                        } else {
                                                parentId = contourPrime.ParentId
                                        }
                                }

                                p0 := image.Point{j, i}
                                border, collectionIndices, err := createBorder(img, p0, from, nbd, done)
                                if err != nil {
                                        log.Errorf("unable to create border: %s", err.Error())
                                        return nil, err
                                }

                                if len(border) == 0 {
                                        border = append(border, p0)
                                        img.Set(p0, -1*nbd)
                                }

                                if parentId != 0 {
                                        parent := contours[parentId]
                                        parent.Children = append(parent.Children, contour)
                                        contour.Parent = contours[parentId]
                                }
                                contour.ParentId = parentId
                                contour.Points = border
                                contour.Id = nbd
                                contours[nbd] = contour
                                addCollisionFlag(contour, parentId, contours, collectionIndices)
                        }
                        if fji != 0 && fji != 1 {
                                lnbd = fji
                                if lnbd < 0 {
                                        lnbd *= -1
                                }
                        }
                }
        }

        finalContour := contours[1]

        // image was padded... so now shift every co-ord by -1,-1
        if img.HasPadding() {
                shiftContour(finalContour)
        }
        return finalContour, nil
}

func shiftContour(contour *Contour) {
        for i, _ := range contour.Points {
                contour.Points[i].X = contour.Points[i].X - 1
                contour.Points[i].Y = contour.Points[i].Y - 1
        }

        for _, child := range contour.Children {
                shiftContour(child)
        }
}

package border

import (
        "fmt"
        "image"
        "image/color"
        "image/png"
        _ "image/png"
        "os"

        "github.com/kpfaulkner/borders/common"
        image2 "github.com/kpfaulkner/borders/image"
)

// LoadImage loads a PNG and returns a SuzukiImage. Currently restricted to PNG but will eventually expand
// to include other formats.
//
// Erode parameter forces the eroding of the image before converting to a SuzukiImage.
// See https://en.wikipedia.org/wiki/Erosion_(morphology) for explanation
//
// Dilate parameter forces the dilating of the image before converting to a SuzukiImage. Likewise, see
// https://en.wikipedia.org/wiki/Dilation_(morphology) for explanation.
//
// The combination of Erode and Dilate helps remove any "spikes" that may appear in the generated boundary.
// erode and dilate will usually be 0 (none) or 1 (single pixel spikes)
func LoadImage(filename string, erode int, dilate int) (*common.SuzukiImage, error) {

        f, err := os.Open(filename)
        if err != nil {
                return nil, err
        }
        defer f.Close()

        img, _, err := image.Decode(f)
        if err != nil {
                return nil, err
        }

        // If any pixels on the edges are populated, then we need to pad this out by 1 pixel on each side.
        // This will be reversed later.
        requirePadding := doesImageRequirePadding(img)

        // need border to be black. Pad edges with 1 black pixel
        si := common.NewSuzukiImage(img.Bounds().Dx(), img.Bounds().Dy(), requirePadding)

        paddingOffset := 0
        if requirePadding {
                paddingOffset = 1
        }

        // dumb... but convert to own image format for now.
        for y := 0; y < img.Bounds().Dy(); y++ {
                for x := 0; x < img.Bounds().Dx(); x++ {
                        cc := 0
                        c := img.At(x, y)
                        r, g, b, _ := c.RGBA()
                        if !(r == 0 && g == 0 && b == 0) {
                                cc = 1
                        }
                        si.SetXY(x+paddingOffset, y+paddingOffset, cc)
                }

        }

        if erode != 0 {
                si, err = image2.Erode(si, erode)
                if err != nil {
                        return nil, err
                }
        }

        if dilate != 0 {
                si, err = image2.Dilate(si, dilate)
                if err != nil {
                        return nil, err
                }
        }

        return si, nil
}

// check down each edge to see if populated, if so, it will require padding
func doesImageRequirePadding(img image.Image) bool {

        // down left/right edge
        for y := 0; y < img.Bounds().Dy(); y++ {
                leftEdgeX := 0
                c := img.At(leftEdgeX, y)
                r, g, b, _ := c.RGBA()
                if !(r == 0 && g == 0 && b == 0) {
                        return true
                }

                rightEdgeX := img.Bounds().Dx() - 1
                c = img.At(rightEdgeX, y)
                r, g, b, _ = c.RGBA()
                if !(r == 0 && g == 0 && b == 0) {
                        return true
                }
        }

        // across top and bottom
        for x := 0; x < img.Bounds().Dx(); x++ {
                topEdgeY := 0
                c := img.At(x, topEdgeY)
                r, g, b, _ := c.RGBA()
                if !(r == 0 && g == 0 && b == 0) {
                        return true
                }

                bottomEdgeY := img.Bounds().Dy() - 1
                c = img.At(x, bottomEdgeY)
                r, g, b, _ = c.RGBA()
                if !(r == 0 && g == 0 && b == 0) {
                        return true
                }
        }

        return false
}

// SaveImage saves a SuzukiImage as a PNG to given filename.
// Although currently only PNG, will make this more generic in the future.
func SaveImage(filename string, si *common.SuzukiImage) error {

        upLeft := image.Point{0, 0}
        lowRight := image.Point{si.Width, si.Height}

        img := image.NewRGBA(image.Rectangle{upLeft, lowRight})

        for x := 0; x < si.Width; x++ {
                for y := 0; y < si.Height; y++ {
                        p := si.GetXY(x, y)
                        if p == 1 {
                                img.Set(x, y, color.White)
                        } else {
                                img.Set(x, y, color.Black)
                        }
                }
        }

        f, _ := os.Create(filename)
        png.Encode(f, img)
        return nil
}

// SaveContourSliceImage saves a contour (and all child contours) as a PNG.
// Width and height are the dimensions of the image to save.
//
// flipBook is a bool to indicate that when each child contour is added to the image, the image should be
// saved to a new file with the filename suffixed with the count of contours added so far. This is useful
// for debugging and visualising the contours as they are added.
//
// minContourSize indicates if minimum number of points that make up a contour. If contour contains fewer, then
// do NOT save.
func SaveContourSliceImage(filename string, c *Contour, width int, height int, flipBook bool, minContourSize int) error {

        upLeft := image.Point{0, 0}
        lowRight := image.Point{width, height}

        img := image.NewRGBA(image.Rectangle{upLeft, lowRight})

        // naive fill
        for x := 0; x < width; x++ {
                for y := 0; y < height; y++ {
                        img.Set(x, y, color.Black)
                }
        }

        colour := 0
        count := 0

        drawContour(img, c, flipBook, minContourSize, colour, &count, filename)
        f, _ := os.Create(filename)
        png.Encode(f, img)
        return nil
}

// drawContour saves a contour to the provided image and then recursively calls to save children to same image.
func drawContour(img *image.RGBA, c *Contour, flipBook bool, minContourSize int, colour int, count *int, filename string) error {

        colours := []color.RGBA{
                {255, 0, 0, 255},
                {255, 106, 0, 255},
                {255, 216, 0, 255},
                {0, 255, 0, 255},
                {127, 255, 197, 255},
                {72, 0, 255, 255},
                {255, 127, 182, 255},
        }

        max := len(colours)
        if c.BorderType == Outer {
                colour = 0
        }

        // draw contour itself.
        if len(c.Points) > 0 && len(c.Points) > minContourSize {

                colourToUse := colours[colour]
                for _, p := range c.Points {
                        img.Set(p.X, p.Y, colourToUse)
                }
                colour++
                if colour >= max {
                        colour = 0
                }

                // save new image per contour added...  crazy
                if flipBook {
                        fn := fmt.Sprintf("%s-%d.png", filename, *count)
                        f, _ := os.Create(fn)
                        png.Encode(f, img)
                        f.Close()
                }
                *count = *count + 1
        }

        for _, child := range c.Children {
                colour++
                if colour >= max {
                        colour = 0
                }
                *count = *count + 1
                drawContour(img, child, flipBook, minContourSize, colour, count, filename)
        }

        return nil
}

package common

import (
        "fmt"
        "image"
        "strings"
)

// SuzukiImage is the basic structure we use to define an image when trying to find contours.
type SuzukiImage struct {
        Width   int
        Height  int
        data    []int
        dataLen int

        // Indicates if a 1 pixel padding has been applied to around the image.
        // This helps with imagery where it goes RIGHT up to the edge.
        hasPadding bool
}

// NewSuzukiImage creates a new SuzukiImage of specific dimensions.
func NewSuzukiImage(width int, height int, hasPadding bool) *SuzukiImage {
        si := SuzukiImage{}
        padding := 0
        if hasPadding {
                padding = 2
        }
        si.Width = width + padding
        si.Height = height + padding
        si.data = make([]int, si.Width*si.Height)
        si.dataLen = si.Width * si.Height // just saves us calculating a lot
        si.hasPadding = hasPadding
        return &si
}

func NewSuzukiImageFromData(width int, height int, hasPadding bool, data []int) *SuzukiImage {
        si := NewSuzukiImage(width, height, hasPadding)
        si.data = data[:]
        si.dataLen = len(data)
        return si
}

// Get returns the value of a given point
func (si *SuzukiImage) GetAllData() []int {
        return si.data
}

// Get returns the value of a given point
func (si *SuzukiImage) Get(p image.Point) int {
        idx := p.Y*si.Width + p.X
        return si.data[idx]
}

// GetXY returns the value of a given x/y
func (si *SuzukiImage) GetXY(x int, y int) int {
        idx := y*si.Width + x
        return si.data[idx]
}

// Set sets the value at a given point
func (si *SuzukiImage) Set(p image.Point, val int) {
        idx := p.Y*si.Width + p.X
        si.data[idx] = val
}

// SetXY sets the value at a given x/y
func (si *SuzukiImage) SetXY(x int, y int, val int) {
        idx := y*si.Width + x
        si.data[idx] = val
}

func (si *SuzukiImage) HasPadding() bool {
        return si.hasPadding
}

// DisplayAsText generates a string of a given image. This is purely used for debugging SMALL images
func (si *SuzukiImage) DisplayAsText() []string {
        s := []string{}
        for y := 0; y < si.Height; y++ {
                ss := si.data[y*si.Width : (y*si.Width + si.Width)]
                t := []string{}
                for _, i := range ss {
                        t = append(t, fmt.Sprintf("%d", i))
                }
                s = append(s, strings.Join(t, " ")+"\n")
        }

        return s
}

// Equals checks if two SuzukiImages are equal.
func (si *SuzukiImage) Equals(other *SuzukiImage) bool {
        if si.Width != other.Width || si.Height != other.Height {
                return false
        }

        for i := 0; i < si.dataLen; i++ {
                if si.data[i] != other.data[i] {
                        return false
                }
        }
        return true
}

package converters

import (
        "errors"
        "image"
        "math"

        "github.com/kpfaulkner/borders/border"
        "github.com/peterstace/simplefeatures/geom"
)

const (
        EarthRadius       = 6378137.0
        toleranceInMetres = 2
)

type PointConverter func(x float64, y float64) (float64, float64)

// NewSlippyToLatLongConverter returns a function that converts slippy tile coordinates to lat/long.
func NewSlippyToLatLongConverter(slippyXOffset float64, slippyYOffset float64, scale int) func(X float64, Y float64) (float64, float64) {
        latLongN := math.Pow(2, float64(scale))
        f := func(x float64, y float64) (float64, float64) {
                long, lat := slippyCoordsToLongLat(slippyXOffset, slippyYOffset, x, y, latLongN)
                return long, lat
        }
        return f
}

// LatLongToSlippy converts lat/long to slippy tile coordinates.
func LatLongToSlippy(latDegrees float64, longDegrees float64, scale int) (float64, float64) {
        n := math.Exp2(float64(scale))
        x := int(math.Floor((longDegrees + 180.0) / 360.0 * n))
        if float64(x) >= n {
                x = int(n - 1)
        }
        y := int(math.Floor((1.0 - math.Log(math.Tan(latDegrees*math.Pi/180.0)+1.0/math.Cos(latDegrees*math.Pi/180.0))/math.Pi) / 2.0 * n))
        return float64(x), float64(y)

}

// ConvertContourToPolygon converts the contours (set of x/y coords) to geometries commonly used in the GIS space
// Convert to polygons, then simplify (if required) while still in "pixel space"
// Only then apply conversions which may be to lat/long (or any other conversions).
// Simplifying while in "pixel space" simplifies the simplification degTolerance calculation.
// params:
//
//                simplify: Simplify the resulting polygons
//            minPoints: Minimum number of vertices for a polygon to be considered valid. If less than this, then will be discarded. 0 means no minimum
//                degTolerance: Tolerance in pixels when simplifying. If set to 0, then will use defaults.
//                multiPolygonOnly: If the geometry is results in a GeometryCollection, then extract out the multipolygon part and return that.
//                pointConverters: Used to convert point co-ord systems. eg. slippy to lat/long.
func ConvertContourToPolygon(c *border.Contour, scale int, simplify bool, minPoints int, tolerance float64, multiPolygonOnly bool, pointConverters ...PointConverter) (*geom.Geometry, error) {
        polygons := []geom.Polygon{}

        err := convertContourToPolygons(c, minPoints, &polygons)
        if err != nil {
                return nil, err
        }

        mp := geom.NewMultiPolygon(polygons)

        if simplify {
                if tolerance == 0 {
                        tolerance = generateSimplifyTolerance(scale)
                }
                gg := mp.AsGeometry()
                simplifiedGeom, err := gg.Simplify(tolerance, geom.NoValidate{})
                if err != nil {
                        return nil, err
                }

                if multiPolygonOnly {
                        if simplifiedGeom.Type() == geom.TypeMultiPolygon {
                                mp, _ = simplifiedGeom.AsMultiPolygon()
                                return returnConvertedGeometry(&mp, pointConverters...)
                        }

                        ////////////////////////
                        // Need to check if this is still possible.
                        // need to check when we get geometrycollection vs multipolygon
                        //if simplifiedGeom.Type() == geom.TypeGeometryCollection {
                        //        gc, ok := simplifiedGeom.AsGeometryCollection()
                        //        if ok {
                        //                mp, err := filterMultiPolygonFromGeometryCollection(&gc)
                        //                if err == nil {
                        //                        return returnConvertedGeometry(mp, pointConverters...)
                        //                }
                        //        }
                        //}
                        ////////////////////////
                        return nil, errors.New("unable to filter multipolygon from geometry collection")
                }

                mp, ok := simplifiedGeom.AsMultiPolygon()
                if ok {
                        return returnConvertedGeometry(&mp, pointConverters...)
                } else {
                        return nil, errors.New("unable to convert simplified geom to multipolygon")
                }
        }
        return returnConvertedGeometry(&mp, pointConverters...)
}

// returnConvertedGeometry converts the multipolygon with PointConverters (if supplied)
// Can be used to help convert to lat/long or any other co-ordinate system.
func returnConvertedGeometry(mp *geom.MultiPolygon, pointConverters ...PointConverter) (*geom.Geometry, error) {
        finalMultiPoly, err := convertCoords(mp, pointConverters...)
        if err != nil {
                return nil, err
        }
        g := finalMultiPoly.AsGeometry()
        return &g, nil
}

// convertCoords converts the coordinates of a multipolygon using the supplied PointConverters.
func convertCoords(mp *geom.MultiPolygon, converters ...PointConverter) (*geom.MultiPolygon, error) {

        mp2 := mp.TransformXY(func(xy geom.XY) geom.XY {
                x := xy.X
                y := xy.Y
                // run through converters.
                for _, converter := range converters {
                        newX, newY := converter(x, y)
                        x = newX
                        y = newY
                }
                return geom.XY{X: x, Y: y}
        })

        return &mp2, nil

}

// generateLineString generates a LineString from a slice of image.Points.
func generateLineString(points []image.Point) (*geom.LineString, error) {
        seq := pointsToSequence(points)

        if seq.Length() > 2 {
                ls := geom.NewLineString(seq)

                // if linestring only has 1 value, then ditch.
                if seq.Length() >= 1 {
                        return &ls, nil
                }
        }

        return &geom.LineString{}, nil
}

// convertContourToPolygons converts the contour to a set of polygons but does NOT convert to different co-ord systems.
// If a polygon has fewer than minPoints then it will be discarded. 0 means no min points.
func convertContourToPolygons(c *border.Contour, minPoints int, polygons *[]geom.Polygon) error {

        // outer... so make a poly
        // will also cover hole if there.
        if c.BorderType == border.Outer {

                lineStrings := []geom.LineString{}
                outerLS, err := generateLineString(c.Points)
                if err != nil {
                        return err
                }
                lineStrings = append(lineStrings, *outerLS)

                // now get children... (holes).
                for _, child := range c.Children {
                        if !child.ParentCollision && child.Usable {
                                ls, err := generateLineString(child.Points)
                                if err != nil {
                                        return err
                                }
                                lineStrings = append(lineStrings, *ls)
                        }
                }

                var poly geom.Polygon
                if minPoints == 0 || len(lineStrings) > minPoints {
                        poly = geom.NewPolygon(lineStrings)
                        *polygons = append(*polygons, poly)
                }
        }

        for _, child := range c.Children {
                // only process child if no conflict with parent.
                if !child.ParentCollision && child.Usable {
                        err := convertContourToPolygons(child, minPoints, polygons)
                        if err != nil {
                                return err
                        }
                }
        }

        return nil
}

// pointsToSequence converts a slice of image.Points to a geom.Sequence.
func pointsToSequence(points []image.Point) geom.Sequence {
        s := len(points)*2 + 2
        seq := make([]float64, s, s)
        index := 0
        for _, origP := range points {
                x, y := float64(origP.X), float64(origP.Y)
                seq[index] = x
                seq[index+1] = y
                index += 2
        }

        seq[index] = seq[0]
        seq[index+1] = seq[1]
        return geom.NewSequence(seq, geom.DimXY)
}

// slippyCoordsToLongLat converts to lat/long... and requires the slippy offset of top left corner of area.
func slippyCoordsToLongLat(slippyXOffset float64, slippyYOffset float64, xTile float64, yTile float64, latLongN float64) (float64, float64) {
        x := xTile + slippyXOffset
        y := yTile + slippyYOffset

        longDeg := (x/latLongN)*360.0 - 180.0
        latRad := math.Atan(math.Sinh(math.Pi - (y/latLongN)*2*math.Pi))
        latDeg := latRad * (180.0 / math.Pi)

        return longDeg, latDeg
}

// generateSimplifyTolerance will mainly be used when we want to convert to geographical co-ordinates
// By default we will determine how many metres per pixel (for input scale/zoom) and double it.
func generateSimplifyTolerance(scale int) float64 {
        mtrPerPixel := metresPerPixel(scale)
        tolerance := mtrPerPixel * toleranceInMetres
        return tolerance
}

// tileSizeInMetres is the size of a tile in metres.
func tileSizeInMetres(scale int) float64 {
        return 2 * math.Pi * EarthRadius / float64(uint64(1)<<uint64(scale))
}

// metresPerPixel is number of metres for a given input pixel. This is based on the scale/zoom.
func metresPerPixel(scale int) float64 {
        return tileSizeInMetres(scale) / 256.0
}

// filterMultiPolygonFromGeometryCollection currently unused. Will be used in upcoming version.
func filterMultiPolygonFromGeometryCollection(col *geom.GeometryCollection) (*geom.MultiPolygon, error) {
        var mp geom.MultiPolygon
        var ok bool
        for i := 0; i < col.NumGeometries(); i++ {
                g := col.GeometryN(i)
                mp, ok = g.AsMultiPolygon()
                if ok {
                        return &mp, nil
                }
        }

        return nil, errors.New("no multipolygon found in geometry collection")
}

package image

import (
        "github.com/kpfaulkner/borders/common"
)

// Erode the suzuki image, based on Morphological Erosion
// https://en.wikipedia.org/wiki/Erosion_(morphology)
// Although based on the above, we always need to make sure the border of the image is all 0.
func Erode(img *common.SuzukiImage, radius int) (*common.SuzukiImage, error) {

        img2 := common.NewSuzukiImage(img.Width, img.Height, img.HasPadding())
        for y := 0; y < img.Height; y++ {
                for x := 0; x < img.Width; x++ {

                        // if x == 0 or y == 0 or x == img.Width-1 or y == img.Height-1 then its an edge, and set it to 0.
                        if x == 0 || y == 0 || x == img.Width-1 || y == img.Height-1 {
                                img.SetXY(x, y, 0)
                                continue
                        }

                        // for each pixel, check if all pixels within radius are 1
                        // if not, set to 0
                        if img.GetXY(x, y) == 1 {
                                // check if all pixels within radius are 1
                                // if not, set to 0
                                if !checkErodeRadius(img, x, y, img.Width, img.Height, radius) {
                                        img2.SetXY(x, y, 0)
                                } else {
                                        img2.SetXY(x, y, 1)
                                }
                        }
                }
        }
        return img2, nil
}

func checkErodeRadius(img *common.SuzukiImage, x int, y int, width int, height int, radius int) bool {
        for i := -radius; i <= radius; i++ {
                for j := -radius; j <= radius; j++ {
                        if x+i < 0 || y+j < 0 || x+i >= width || y+j >= height {
                                continue // out of bounds.
                        }
                        if img.GetXY(x+i, y+j) != 1 {
                                return false
                        }
                }
        }
        return true
}

// Dilate the suzuki image, based on Morphological Dilation
// https://en.wikipedia.org/wiki/Dilation_(morphology)
func Dilate(img *common.SuzukiImage, radius int) (*common.SuzukiImage, error) {
        img2 := common.NewSuzukiImage(img.Width, img.Height, img.HasPadding())

        for y := 0; y < img.Height; y++ {
                for x := 0; x < img.Width; x++ {

                        // for each pixel, check if any pixels within radius are 1
                        // if not, set to 0
                        if img.GetXY(x, y) == 1 {
                                dilateRadiusAroundPoint(img2, x, y, img.Width, img.Height, radius)
                        }
                }
        }
        return img2, nil
}

func dilateRadiusAroundPoint(img2 *common.SuzukiImage, x int, y int, width int, height int, radius int) {
        for i := -radius; i <= radius; i++ {
                for j := -radius; j <= radius; j++ {
                        if x+i < 0 || y+j < 0 || x+i >= width || y+j >= height {
                                continue // out of bounds.
                        }
                        img2.SetXY(x+i, y+j, 1)
                }
        }
}