kml.go

package heatmap

import (
	"archive/zip"
	"errors"
	"fmt"
	"image"
	"image/color"
	"image/png"
	"io"
)

const kmlStart = `<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
<Folder>`
const kmlOverlay = `
    <GroundOverlay>
      <Icon>
        <href>%s</href>
      </Icon>
      <LatLonBox>
        <north>%2.16f</north>
        <south>%2.16f</south>
        <east>%2.16f</east>
        <west>%2.16f</west>
        <rotation>0</rotation>
      </LatLonBox>
    </GroundOverlay>`
const kmlEnd = `</Folder></kml>`

const kml = kmlStart + kmlOverlay + kmlEnd

// KML generates a heatmap for geographical data and the kml required to render it.
func KML(size image.Rectangle, points []DataPoint, dotSize int, opacity uint8,
	scheme []color.Color, imgurl string, out io.Writer) (image.Image, error) {

	limits := findLimits(points)
	if !limits.inRange(-180, 180, -90, 90) {
		return nil, errors.New("limits out of range")
	}

	mapimg := Heatmap(size, points, dotSize, opacity, scheme)

	adjustedLimits := adjustLimits(limits, size, dotSize)

	_, err := fmt.Fprintf(out, kml, imgurl,
		adjustedLimits.Max.Y(),
		adjustedLimits.Min.Y(),
		adjustedLimits.Max.X(),
		adjustedLimits.Min.X())

	return mapimg, err
}

func must(err error) {
	if err != nil {
		panic(err)
	}
}

// KMZ generates a heatmap for geographical data as a kmz.
func KMZ(size image.Rectangle, points []DataPoint, dotSize int, opacity uint8,
	scheme []color.Color, out io.Writer) error {

	z := zip.NewWriter(out)
	defer z.Close()
	dockml, err := z.Create("doc.kml")
	must(err) // no known condition can cause failure here

	img, err := KML(size, points, dotSize, opacity, scheme,
		"heatmap.png", dockml)
	if err != nil {
		return err
	}

	imgf, err := z.Create("heatmap.png")
	must(err) // Can't induce failure here, either

	return png.Encode(imgf, img)
}

func adjustLimits(limits limits, size image.Rectangle, dotSize int) (rv limits) {
	halfdot := float64(dotSize) / 2.0
	offx := (halfdot / float64(size.Dx()-dotSize)) * float64(limits.Dx())
	offy := (halfdot / float64(size.Dy()-dotSize)) * float64(limits.Dy())

	rv.Min = P(limits.Min.X()-offx, limits.Min.Y()-offy)
	rv.Max = P(limits.Max.X()+offx, limits.Max.Y()+offy)
	return
}