public static void makeHeatmap(int radius) throws Exception {
    Scanner scan = new Scanner(new File("/Users/leijurv/Downloads/heatmap_overworld_full.csv"));
    // from -radius to +radius-1
    BufferedImage output = new BufferedImage(radius * 2, radius * 2, BufferedImage.TYPE_BYTE_GRAY);
    WritableRaster raster = output.getRaster();
    SampleModel model = raster.getSampleModel();
    DataBuffer buffer = raster.getDataBuffer();
    for (int x = 0; x < 2 * radius; x++) {
        for (int y = 0; y < 2 * radius; y++) {
            model.setSample(x, y, 0, 255, buffer);
        }
    }
    int i = 0;
    while (scan.hasNextLine()) {
        if (++i % 1000000 == 0) {
            System.out.println(i);
        }
        String line = scan.nextLine();
        String[] split = line.split(",");
        int chunkX = Integer.parseInt(split[0]);
        int chunkZ = Integer.parseInt(split[1]);
        int imageX = chunkX + radius;
        int imageY = chunkZ + radius;
        if (imageX < 0 || imageX >= 2 * radius || imageY < 0 || imageY >= 2 * radius) {
            continue;
        }
        int weight = Integer.parseInt(split[2]);
        int color = 255 - (int) (50 * Math.log(weight)) - 50;
        if (color < 0) {
            color = 0;
        }
        if (color > 255) {
            color = 255;
        }
        model.setSample(imageX, imageY, 0, color, buffer);
    }
    File o = new File("/Users/leijurv/Downloads/heatmap_overworld_full.png");
    ImageIO.write(output, "png", o);
}