GeoPoint rendering using gfx.

gfx-geo-countries.go

package main

import (
	"image/draw"
	"io"
	"strconv"
	"text/scanner"

	"github.com/peterhellberg/gfx"
)

const tileSize, zoom float64 = 170, 5

var move = gfx.V(-2600, 1450)

func main() {
	dst := gfx.NewImage(768, 768, gfx.BlockColorBlack.Dark)

	drawCountry(dst, "sweden", gfx.GP(59.3293, 18.0686), gfx.BlockColorBlue)
	drawCountry(dst, "finland", gfx.GP(60.1699, 24.9384), gfx.BlockColorWhite)
	drawCountry(dst, "denmark", gfx.GP(55.6761, 12.5683), gfx.BlockColorRed)
	drawCountry(dst, "germany", gfx.GP(52.5200, 13.4050), gfx.BlockColorOrange)

	gfx.SavePNG("gfx-geo-countries.png", dst)
}

func drawCountry(dst draw.Image, country string, city gfx.GeoPoint, bc gfx.BlockColor) {
	downloadPoly(country).Fill(dst, bc.Medium)
	gfx.DrawCircleFilled(dst, city.Vec(tileSize, zoom).Add(move), 6, bc.Dark)
}

func downloadPoly(country string) gfx.Polygon {
	rawurl := gfx.Sprintf("https://download.geofabrik.de/europe/%s.poly", country)

	resp, err := gfx.Get(rawurl)
	if err != nil || resp.StatusCode != 200 {
		return gfx.Polygon{}
	}
	defer resp.Body.Close()

	return scanPoly(resp.Body).Project(gfx.IM.Moved(move))
}

func scanPoly(r io.Reader) gfx.Polygon {
	var s scanner.Scanner

	s.Init(r)

	var floats []float64

	for tok := s.Scan(); tok != scanner.EOF; tok = s.Scan() {
		switch tok {
		case scanner.Float:
			if f, err := strconv.ParseFloat(s.TokenText(), 64); err == nil {
				floats = append(floats, f)
			}
		}
	}

	var p gfx.Polygon

	for i := len(floats) - 2; i >= 0; i -= 2 {
		p = append(p, gfx.GP(floats[i+1], floats[i]).Vec(tileSize, zoom))
	}

	return p
}