Tokyo Bay Height Map Creator

// for LINQPad 5

var http = new HttpClient();

var tile_start = new int[]{1819-2,806-3};
var tile_range = 10;
var tile_zoom = 11;
var bmp = new Bitmap(tile_range*256,tile_range*256);

for(var pixel_x = 0;pixel_x < tile_range*256;pixel_x++) {
for(var pixel_y = 0;pixel_y < tile_range*256;pixel_y++) {
bmp.SetPixel(pixel_x,pixel_y,Color.Black);
}
}

for(var count_x = 0; count_x < tile_range;count_x++) {
for(var count_y = 0; count_y < tile_range;count_y++) {
try{
var tile_x = tile_start[0]+count_x;
var tile_y = tile_start[1]+count_y;
var url = $@"https://cyberjapandata.gsi.go.jp/xyz/dem_png/{tile_zoom}/{tile_x}/{tile_y}.png";
var stream = await http.GetStreamAsync(url);
var src_bmp = new Bitmap(stream);

for(var pixel_x = 0;pixel_x < 256;pixel_x++) {
for(var pixel_y = 0;pixel_y < 256;pixel_y++) {

var h = ToHeight(src_bmp.GetPixel(pixel_x,pixel_y));
bmp.SetPixel(pixel_x + count_x * 256,pixel_y + count_y * 256,ToColor(h));
}
}
}catch{}
}
}

for(var count_x = 0; count_x < tile_range;count_x++) {
for(var count_y = 0; count_y < tile_range;count_y++) {
try{
var tile_x = tile_start[0]+count_x;
var tile_y = tile_start[1]+count_y;
var url = $@"https://cyberjapandata.gsi.go.jp/xyz/lcm25k_2012/{tile_zoom}/{tile_x}/{tile_y}.png";
var stream = await http.GetStreamAsync(url);
var src_bmp = new Bitmap(stream);

for(var pixel_x = 0;pixel_x < 256;pixel_x++) {
for(var pixel_y = 0;pixel_y < 256;pixel_y++) {

var color = src_bmp.GetPixel(pixel_x,pixel_y);
if(color.R == 101 && color.G == 202 && color.B >= 250) {

bmp.SetPixel(pixel_x + count_x * 256,pixel_y + count_y * 256,Color.Black);
}

}
}
}catch{}
}
}


bmp.Dump();

Color ToColor(double height) {
  var min = -40.0;
  var max = 300;

  if(height > max/2) height = max/4 + height/2;

  var value =
    (height - min) / (max - min) * 255;
  if(height < 1) value = 0;

  value = Math.Max(0,Math.Min(255,value));

  return Color.FromArgb((int)value,(int)value,(int)value);
}

double ToHeight(Color color) {
var pow2_8 = 256;
var pow2_16 = 65536;
var pow2_23 = 8388608;
var pow2_24 = 16777216;

var r = color.R;
          var g = color.G;
          var b = color.B;
          var h = 0.0;
          if (r != 128 || g != 0 || b != 0) {
            var d = r * pow2_16 + g * pow2_8 + b;
            h = (d < pow2_23) ? d : d - pow2_24;
            if (h == -pow2_23) h = 0;
            else h *= 0.01;
            return h;
          }
  return -9999;
}