Occlusion Queries with Clipping Planes

I wrote a program to learn how to use the occlusion queries. However, I found the clipping planes of OpenGL do not work with the occlusion queries. The clipping planes didn’t affect the results of occlusion queries. My graphic card is based on nVidia GeForce 4 Ti4200 chipset. Is this just due to the implementation of the nVidia?

Thanks in advance.

It is probably the result of NVIDIA’s implementation. Apparently they use texture units to clip so those clipped fragments probably erroneously still produce fragments they shouldn’t for the test in question.