private static Bitmap DrawSingleCoordinate(Bitmap bitmap, Font font, Color fontColor, Point vertex, Point coordinates)
        {
            Graphics graphics = Graphics.FromImage(bitmap);

            string text = coordinates.ToString();

            float x = vertex.X;
            float y = vertex.Y;

            SizeF  size         = graphics.MeasureString(text, font);
            Bitmap stringBitmap = new Bitmap((int)size.Width, (int)size.Height);

            Graphics.FromImage(stringBitmap).DrawString(text, font, new SolidBrush(fontColor), 0, 0);

            stringBitmap.RotateFlip(RotateFlipType.RotateNoneFlipY);
            graphics.DrawImage(stringBitmap, x, y);

            return(bitmap);
        }