🤔 [QUESTION]密度热力图如何保证数据点在背景图片上位置的准确

### 🐛 Question description [Please make everyone to understand it]
背景图片是我自己上传的一张图片，数据点的坐标就是该点在图片上的位置（以图片左下角为原点，与坐标轴原点保持一致），但是显示到页面上数据点在图片上的位置好像就不对了，那我该如何保证数据点显示在图片上准确的位置呢？
### 💻 Link to minimal reproduction

Please provide a link by forking these links [g2plot](https://codesandbox.io/s/g2plot-reproduction-template-gyej1) or GitHub repo. What is a minimal reproduction, and why is it required?

### 🏞 Expected result

### 🚑 Any additional [like screenshots]https://g2plot.antv.antgroup.com/zh/examples/heatmap/density/#basic

* **G2Plot Version**:
* **Platform**:

Start with the linked density heatmap example at https://g2plot.antv.antgroup.com/zh/examples/heatmap/density/#basic and inspect how the uploaded background image and point coordinates are configured. Reproduce the reported coordinate mismatch with a minimal example; done means the data points align with their intended positions on the image.

Written by the indexing model from the issue text.