Sliders to set max angle and "fold" of offset synthetics

[EvanBianco]

In 1-D It would be good to control the max angle of the synthetic gather.

At the time of writing, I think the max is 30 degrees, fold is 10, which is good. 30 degrees also happens to be the angle which we compute the gradient, for instance, used in stochastic AVO crossplots.

We could add a max angle slider, up to at least 60 degrees, maybe even up to ninety degrees, though I am sure this would cause some wild looking wiggle plots when reflection coefficients approach the critical angle. We'll probably have to clip the plot or deal with it in some other manner. Indeed I think it is reasonable to deal with large angles; one use case is crosswell seismic.

It would also be good to add a slider for the number of traces in the offset synthetic. The current value is fixed to 10.

I see the use case where I want to set the max angle to 45 degrees, and I want to set the number of traces to 2. In that scenario, the first trace would be the zero-offset trace, the second trace would be the far-offset trace; two critical signals for Shuey two-term-like intercept/gradient calculation. Gradient would be far offset trace divided by near offset trace (which we are doing hard coded at 30 deg).

I'm thinking both of these sliders can go with the frequency slider in the gathers menu.

[kwinkunks]

I'd be happy to see 60 deg as the max, assuming we're doing full Zoeppritz. If this is an approximation, then let's keep it in the realm of the model.