Interpolate

package gojts


const DISTMIN = 0.000001

type Segment struct {
    Start, End geom.XY
}

func (s Segment) Length() float64 {
    return s.End.Sub(s.Start).Length()
}

/**
x := segment.Start.X + (segment.End.X-segment.Start.X)*0.4
y := segment.Start.Y + (segment.End.Y-segment.Start.Y)*0.4
fmt.Println(x, y)

fmt.Println(segment.Start.Add(segment.End.Sub(segment.Start).Scale(rate)))
**/
func distValid(dist float64) {
    if dist < DISTMIN {
        panic("dist can not < 0")
    }
}
func (s Segment) Interpolate(dist float64) geom.XY {
    distValid(dist)
    length := s.Length()
    if dist < length {
        rate := dist / length
        return s.Start.Add(s.End.Sub(s.Start).Scale(rate))
    } else {
        return s.End
    }
}

func Interpolate(linestring geom.LineString, dist float64) geom.XY {
    distValid(dist)
    seq := linestring.Coordinates()
    for i := 0; i < seq.Length(); i++ {
        segment := Segment{Start: seq.GetXY(i), End: seq.GetXY(i + 1)}
        length := segment.Length()
        if dist <= length {
            return segment.Interpolate(dist)
        } else {
            dist -= length
        }
    }
    return geom.XY{X: -9999, Y: -9999}
}

package gojts

type Segment2 struct {
    Start, End r2.Vec
}

func (s Segment2) Length() float64 {
    return r2.Norm(r2.Sub(s.End, s.Start))
}

func (s Segment2) Interpolate(dist float64) r2.Vec {
    distValid(dist)
    length := s.Length()
    if dist < length {
        rate := dist / length
        return r2.Add(s.Start, r2.Scale(rate, r2.Sub(s.End, s.Start)))
    } else {
        return s.End
    }
}

func Interpolate2(linestring geom.LineString, dist float64) r2.Vec {
    distValid(dist)
    coords := linestring.Coords()
    for i := 0; i < len(coords); i++ {
        start := coords[i]
        end := coords[i+1]
        segment := Segment2{Start: r2.Vec{X: start[0], Y: start[1]}, End: r2.Vec{X: end[0], Y: end[1]}}
        length := segment.Length()
        if dist <= length {
            return segment.Interpolate(dist)
        } else {
            dist -= length
        }
    }
    return r2.Vec{X: -9999, Y: -9999}
}