Add tiles management

tiles/grid.go

@@ -0,0 +1,33 @@
+package tiles
+
+import "github.com/paulmach/orb"
+
+// GridId defines the position of a tile
+// It follows the Valhalla way of handling tiles : https://github.com/Telenav/open-source-spec/blob/master/valhalla/doc/valhalla-tiles-basic.md
+type GridId uint64
+
+const tilesize float64 = 1.0
+
+// PointGridId returns the id on the grid for a given point
+func PointGridId(point orb.Point) GridId {
+	width := int64(360 / tilesize)
+	return GridId(int64((point.Lat()+90)/tilesize)*width + int64((point.Lon()+180)/tilesize))
+}
+
+// LineStringGridIds returns the list of ids on the grid the linestring goes through.
+// In some really specific cases on tile edges, this could be unaccurate if the polyline was too much simplified
+func LineStringGridIds(linestring orb.LineString) []GridId {
+	results := []GridId{}
+
+	gidmap := map[int64]bool{}
+
+	for _, p := range linestring {
+		gid := PointGridId(p)
+		if _, ok := gidmap[int64(gid)]; !ok {
+			gidmap[int64(gid)] = true
+			results = append(results, gid)
+		}
+	}
+
+	return results
+}