indexer_appengine.go

package main

import (
	"encoding/gob"
	"fmt"
	"net/http"
	"strconv"

	itsk "github.com/prl900/intersekt"
	"google.golang.org/appengine"
)

const (
	sinuProj = "+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +a=6371007.181 +b=6371007.181 +units=m +no_defs "
	tileSize = 2400
)

var modisGeot = []float64{-20015109.3539999984204769, 463.3127165279165069, 0.0, 10007554.677005993, 0.0, -463.3127165279165069}

func GetChunkLoop(i, j int) (*itsk.Loop, error) {

	id := float64(i)
	jd := float64(j)

	tl := itsk.Point{modisGeot[0] + id*tileSize*modisGeot[1], modisGeot[3] + jd*tileSize*modisGeot[5]}
	tr := itsk.Point{modisGeot[0] + (id+1)*tileSize*modisGeot[1], modisGeot[3] + jd*tileSize*modisGeot[5]}
	br := itsk.Point{modisGeot[0] + (id+1)*tileSize*modisGeot[1], modisGeot[3] + (jd+1)*tileSize*modisGeot[5]}
	bl := itsk.Point{modisGeot[0] + id*tileSize*modisGeot[1], modisGeot[3] + (jd+1)*tileSize*modisGeot[5]}

	return itsk.NewLoop([]itsk.Point{tl, tr, br, bl}, j, i)
}

func GetLoops() ([]itsk.Loop, error) {
	loops := make([]itsk.Loop, 36*18)
	for i := 0; i < 36; i++ {
		for j := 0; j < 18; j++ {
			l, err := GetChunkLoop(i, j)
			if err != nil {
				return loops, err
			}
			loops[36*j+i] = *l
		}
	}

	return loops, nil
}

func GetMCD43A4Objects(x0, y0, res float64, xSize, ySize int) ([]string, error) {
	out := []string{}

	loops, err := GetLoops()
	if err != nil {
		return out, err
	}

	tl := itsk.Point{x0, y0}
	tr := itsk.Point{x0 + float64(xSize)*res, y0}
	br := itsk.Point{x0 + float64(xSize)*res, y0 - float64(ySize)*res}
	bl := itsk.Point{x0, y0 - float64(ySize)*res}

	a, err := itsk.NewLoop([]itsk.Point{tl, tr, br, bl}, 0, 0)
	if err != nil {
		return out, err
	}

	b := a.Transform(sinuProj)
	//sa := a.Segmentize(2)
	//sb := sa.Transform(sinuProj)

	for _, l := range loops {
		if b.Intersects(&l) {
			out = append(out, fmt.Sprintf("MCD43A4.A2017007.h%02dv%02d.006_B01.TIF", l.H, l.V))
		}
	}

	return out, nil
}

func handle(w http.ResponseWriter, r *http.Request) {

	q := r.URL.Query()
	xSize, err := strconv.Atoi(q.Get("xsize"))
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		w.Write([]byte("400 - Malformed request!"))
		return
	}

	ySize, err := strconv.Atoi(q.Get("ysize"))
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		w.Write([]byte("400 - Malformed request!"))
		return
	}

	x0, err := strconv.ParseFloat(q.Get("x0"), 64)
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		w.Write([]byte("400 - Malformed request!"))
		return
	}

	y0, err := strconv.ParseFloat(q.Get("y0"), 64)
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		w.Write([]byte("400 - Malformed request!"))
		return
	}

	res, err := strconv.ParseFloat(q.Get("res"), 64)
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		w.Write([]byte("400 - Malformed request!"))
		return
	}

	objs, err := GetMCD43A4Objects(x0, y0, res, xSize, ySize)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		w.Write([]byte("500 - Something bad happened!"))
		return
	}

	w.Header().Set("Content-Type", "application/octet-stream")
	enc := gob.NewEncoder(w)
	err = enc.Encode(objs)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		w.Write([]byte("500 - Something bad happened!"))
	}
}

func main() {
	http.HandleFunc("/", handle)
	appengine.Main()
}