add dem

pkg/dem/dem.go

@@ -0,0 +1,70 @@
+package dem
+
+import (
+	"math"
+
+	"github.com/airbusgeo/godal"
+	log "github.com/sirupsen/logrus"
+)
+
+type Dem1Km struct {
+	File          string
+	LT            [][]float32
+	width, height int
+	wUnit         float32 // degree per pixel
+	hUnit         float32 // degree per pixel
+}
+
+var Dem1KmLT *Dem1Km
+
+func NewDem1Km(file string) *Dem1Km {
+	d := &Dem1Km{
+		File: file,
+	}
+
+	if err := d.Load(); err != nil {
+		log.Error("cannot load DEM file", err)
+	}
+	return d
+}
+
+func (d *Dem1Km) Load() error {
+	hDataset, err := godal.Open(d.File)
+	if err != nil {
+		return err
+	}
+
+	band := hDataset.Bands()[0]
+
+	structure := band.Structure()
+
+	for y := 1; y <= structure.SizeY; y++ {
+		scanline := make([]float32, structure.SizeX)
+		err = band.Read(0, y, scanline, structure.SizeX, 1)
+		if err != nil {
+			return err
+		}
+		d.LT = append(d.LT, scanline)
+	}
+
+	d.wUnit = 360.0 / float32(structure.SizeX)
+	d.hUnit = 180.0 / float32(structure.SizeY)
+	d.width = structure.SizeX
+	d.height = structure.SizeY
+
+	return nil
+}
+
+func (d *Dem1Km) Elevation(lng, lat float64) float32 {
+	lng = math.Abs(lng + 180.0)
+	lat = math.Abs(lat - 90.0)
+	w := int(lng / float64(d.wUnit))
+	h := int(lat / float64(d.hUnit))
+
+	if w > d.width-1 || h > d.height-1 {
+		return 0.0
+	}
+
+	return d.LT[h][w]
+
+}