Customizable SVP interpolation options

A user requests being able to chose the line along which casts are interpolated. I added an image for clarification; essentially his issue is that when he's working in an area with current, instead of choosing to interpolate between the closest casts in distance or time, he wants to be able to chose which casts to "draw a line" between; in his example he wants casts that are across the river from each other instead of down river, where there's likely to be more dynamic changes. Reach out to me if you want me to try to explain it better.