Many times it has come up that users/developers want to find out which ra/dec points overlap a given exposure. Unfortunately, converting the ra/dec to x/y often fails due to extrapolation issues. The other way works, but there are a few lines to convert a bbox to a sphgeom convex polygon (given a wcs) that aren't obvious. This will add a convenience method to the exposure class in python to return this convex polygon (though necessarily approximate because of projections). This will allow poly.contains() and other manipulations of the sphgeom polygon.