This would seem to be an easy task but in fact it's not. With a pointy
mountain you can always easily answer the question "Which mountains can see
the point peak?" by simply choosing the pointy peak as your viewpoint and
getting the list of visible peaks. Pointy peaks have the advantage that from
their summit you can see unobstructed in all directions - so any peak you can
see from there can also see you. Makes sense...
The problem with Rainier is that it isn't pointy. It's bulk is so large
that there is no single spot on or near it's summit where you have an
unobstructed view in all direction. The mountain's own bulk blocks the view.
So... what to do?
My general suggestion for a solution: Mount Rainier has several canned
viewpoints that ring the summit. Presumably the union of the visible peaks
from each of these viewpoints is the set of peaks from which Rainier is
I'm not sure exactly how to do this but I'm guessing that you can use the
program to output several CSV files for each of those viewpoints. Read those
CSV files into your favorite spreadsheet program and use your spreadsheet
knowledge to merge those lists and remove duplicates. Voila!