NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2025 Mar 7, 05:28 -0800
Andrés Ruiz, you wrote:
"Basically it uses the calculation of the ephemerides based on a SIMPLIFIED SOLUTION described in Jean Meeus: VSOP87 for planets, ELP2000 for Moon position solution."
The code employs obsolete tools and produces terrible results. Andres, you very diplomatically suggested that it would be "more expensive to modify the code than to start over to achieve the required accuracy."
In more blunt terms, the code is a disaster. The tool is junk. It should probably be declared defunct and abandoned, but that's not a NavList topic.
The problem is deep incompetence in the computations required here. If you visit the github issues page for this plugin, supplied in Rick Gleason's original post three weeks ago, you'll find this gem: "Moon Semi-Diameter and Horizontal Parallax used by Celestial plugin is off by up to +/- 8%." That's insane. If it's really out by 8%, that would be about 4.6 minutes of arc in HP. That's not a little bug... a little 'oops' somewhere. That's a useless product and, arguably, a dangerous product.
If any of you wish to engage further in this "project", then do it via one of the links the original author provided in his message on 12 Feb 2025. Secondary topics emerging from the discussion are OK for NavList messages, but this cannot become a forum to "fix up" some wildly incompetent project. Secondary topics worth considering: why would anyone use code from 25 years ago (Meeus AA ephemeris code for example) in a modern app? Or... is it worth worrying about angular range issue (forcing arguments to 0 to 360° range) in the modern world, as Paul Hirose mentioned? Or... how can you validate star coordinates in modern apps, whether using Hipparcos or Gaia or anything else as a starting point? Is there any definitive, authoritative source for such data? If you wish to discuss this or any related issues, please go ahead and start a new topic (change the subject of the thread). But this "OpenCPN...Plugin" thread will close shortly.
Frank Reed
