To compare the old WCS and jointcal's fit with the "real" distortion, we can use the matched reference catalog to plot a quiver diagram or an interpolated heat map showing how far each star is from its reference star. We may have to think about how to select objects for this plot, since centroiding errors would make it not so useful.

This would probably be most useful for lsstSim, since that has an infinite-precision reference catalog.