A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Harri Ojanen
Date: 2014 Dec 10, 00:40 -0800
Sorry for not replying earlier, but I've been very busy with other things, and I haven't really had time to look at this. By the way, I just posted the source of the program on github (which is a popular website for publishing source code for open source software). Here is a direct link to the file:
You asked about the y-axis scale. I have to say I'm not sure, I need to think about it. This was my best guess, but I may be wrong. The versions described in the Brown-Nassau and Lyukx papers are different, and the process of using the computer is different. It seems there are then subtle differences between the two approaches. At least I had looked at one source for some detail, only to notice later on that it was different in the other version.
The version described by Lyukx (which seems to agree with the one in SI) makes more sense for sight reduction. In that one you use an AP so that latitude and LHA are whole degrees. Those are marked on the base plate. Declination is used as the rotor setting, where a vernier helps. In the Brown-Nassau version declination and LHA are marked on the base, which reduces accuracy if declination is not a whole degree. Latitude is used as the rotor setting, but the vernier is now not really needed, since latitude could be assumed in whole degrees. However, the Brown-Nassau method is much simpler, you get both altitude and azimuth in a single step. Because of the simplicity I'd still like to support both methods. When less accuracy is needed, you could use the simpler method.
Regarding the placement of the verniers: it has been a lot of work to create verniers and all those scales. The software I use is for plotting of mathematical objects. So in fact the grids were the easy part and quickly done, because the software (called "Matplotlib") is really meant for such things. The scales, verniers and texts I need to create manually one by one, and creating them has been several times more work than the grids. E.g., the software provides certain kinds of scales automatically, the type you would put on "ordinary" mathematical plots, but they are not useful here.
In the near future I won't have much time to fine tune the diagrams. Maybe later on, or perhaps somebody else on the list is also interested to work with the code. You will need Python and Matplotlib, both are free software and easily downloaded and installed.