A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2020 Apr 24, 18:56 -0700
While reducing and plotting some sights I became confused. The results did not always make sense. On reflection I decided that a change in terminology was needed. I always take my sights from the same location and I have a gnss receiver. Hence the concept of a DR position is meaningless. Additionally I work sights by methods that have differing requirements for assumed longitude. I have therefore abandoned the use of the terms "DR position" and "assumed position" and now use three positions:
GNSS position. Used with the cos and haversine methods. This is the method used for checking a sextant reading.
Assumed_t. Longitude selected to make the hour angle (t) a whole degree. Latitude a whole degree. Used with 249 and most short methods. Can also use the cos and hav methods.
An exception is the Aquino method. The table lookup begins with t a whole degree. It is not necessary to calcuate the corresponding longitude.
The Aquino table provides an assumed longitude (for which t is not a whole degree).
Assumed_p. Lat and long selected to make plotting easier - typically whole degrees. Used with the cos and laversine methods.
As an example I am at long 175° 05.2'. An obvious value for long_p is 175°.