Hello, I want to use VolumeController to color-map the attributes in the PointData in the vti file. I have tried only one Scalar, and it works very well. I now want to include two Scalars in a PointData so that I can select different scalars for color mapping on the web page, but I don’t know how to organize the vti file format and how to selectively perform color mapping. In my attempts, I found that a PointData can only contain one Scalars in the vti file, and I feel very confused. Hope someone can tell me what should I do, thank you very much! 
This might be a case of multi component volume rendering, where your second scalar is just the second component. @thewtex can tell you more about it, if applicable.
Thank you very much for your reply. The example you gave is very enlightening. I will try it in the code. 