What is the standard of distinguishing these categories of vehicles? 判别类别的标准是什么？

[zjh21]

Thank you again for this great dataset.
When I work on DroneVehicle, I find it hard to distinguish between truck, van, and freight-car by myself as a human. In the bottom right corner of image 08966.jpg in the test set, there is a line of freight-cars. However, they seem a bit more like vans to me. For trucks and freight-cars, it seems that a freight-car always has a container on its back, while a truck does not. Am I correct?
Therefore, I would like to ask -- what is the definition of truck, van, and freight-car?
Thank you very much!

再次感谢这个数据集。
我做实验的时候，发现肉眼很难辨别truck, van和freight-car这三个类别。比如在测试集里08966.jpg图像的右下角有一排freight-car，但是看起来有一点点像van。对truck和freight-car来说，是不是freight-car背后一定有一个集装箱，而truck没有？
所以我想问一下，truck，van和freight-car具体是怎么定义的？
非常感谢！