A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2016 Oct 18, 15:58 -0400
You can modify the spreadsheet to provide a crisper blue overlay by increasing the number of plotted points. I tried to make the image "live" when using the slider bars, so I kept the number of plotted points to a reasonable value. If you are trying to print a static overlay, it won't really matter how long it takes; so feel free to increase that quantity!
You can also modify the latitude at which you plot the overlay. Instead of using the slider bar, find the cell that contains the output of the slider bar and directly enter the decimal value. So if your port is really 60° 38' 23", then input it's decimal equivalent. It's a very modest change to the output, but it's certainly feasible.
There are many other things you can play with, like adding altitude lines for astronomical, nautical and civil twilight. So you turn it into a sunrise/sunset calculator. Of course, you have to be able to plot the sun to do that. Some versions I posted have that facility.
It's been a few years since I created this, it was good fun at the time. If you want the fun and the work, search "azimuthal equidistant" equations. I will caution you that the sign changes will drive you batty!!