Hi folks,

I'm currently working on implementing a couple of plots to help investigate differences between two similar datasets.

I've implemented DifferenceProjectionPlot, RelativeDifferenceProjectionPlot, and AsymmetryProjectionPlot.

These are available at my fork of yt https://bitbucket.org/krafczyk/yt under the bookmark 'features/difference_plot'.

Essentially, Each of these Plots is a subclass of PWViewerMPL like ProjectionPlot, but create's it's FRB by first creating FRBs for the two data sets then applying an operation to each pixel value to get a new derived value which is a part of the new FRB.

For DifferenceProjectionPlot this is simply A-B
For RelativeDifferenceProjectionPlot this is (A-B)/A
For AsymmetryProjectionPlot this is (A-B)/(A+B)

It's already been suggested to me that I can avoid creating three new classes by moving the choice of combination algorithm to a keyword argument, but I'd like to hear more suggestions.

Thanks,
Matthew Krafczyk