I took the VisualQTH app to the club (NSARC) today and tested it with the club computers running the N1MM software, with the help of Dave Shipman VA7AM.
The app now has some extra 'stats features' along the bottom of the window, and looks like this:
Once we had added the requisite lines to the N1MM .ini file to have it send out UDP packets to the VisualQTH machine, the software was tested with the master logging machine in the radio room, and it worked fine. The other two stations also needed to have these configuration lines added - I had wondered whether the master machine would transmit UDP for all logging records send from the slave machines, but this is clearly not how it works.
Once running, we did a few tests, including attempting to send near-simultaneous contacts from two machines, and all seems well. There are some cases where there are no QRZ records available at all for callsigns (in which case the station lat/lon will be 0,0), which VisualQTH should probably not plot, even if it adds a database entry and a 'slot' in the QSL cards column. I'll make a change to the software to avoid plotting stations with no lat/lon, and to use a particular image in the QSL cards column if no details are available online.
There was also talk of validating station callsign formats, but this entails finding some list of all legal formats for all countries around the world, and I'm not sure if such a thing exists. One could probably research this and build a list of validation patterns without much technical difficulty, but that would probably take more time than I have available.
Otherwise, the next steps are to present this to the plenary session of the club at next week's "field day planning" meeting, and see if there are any suggestions that I can relatively easily achieve in the remaining time before the field day on w/e of June 27/28.