在PictureBox中渲染地理坐标点失败，请求协助排查问题

我现在尝试在PictureBox上绘制地理坐标点，但怎么都没效果，实在搞不清楚问题出在哪。我写了代码来计算图像尺寸和实际地理坐标对应的绘制点，但就是不生效，有没有大佬能帮我找找问题？

我的代码如下：

private void renderMap(Points p)
{
    SizeF dimensions = pictureBox1.Image.PhysicalDimension;
    float width = dimensions.Width;
    float height = dimensions.Height;

    PictureBox image = this.pictureBox1;
    Graphics g = Graphics.FromImage(image.Image);

    while (p is not null)
    {
        float x, y;
        x = float.Parse(p.lon) * width / (width - height);
        y = float.Parse(p.lat) * height / (0 - height);

        //Pen p = new Pen(Color.Blue);
        //int c_radius = 200;
        //int first_point1 = (int)(Math.Cos(0) * c_radius + x);
        //int first_point2 = (int)(Math.Sin(0) * c_radius + y);
        //Point point = new Point(first_point1, first_point2);

        Brush aBrush = (Brush)Brushes.Red;
        g.FillRectangle(aBrush, x, y, 300, 300);

        pictureBox1.Image = image.Image;
        p = p.next;
    }
}

我试过各种修改代码的方式，但最后还是改回了我觉得最直接的写法，可问题依然存在。

备注：内容来源于stack exchange，提问作者bitcoinluvr6969