NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Why no interpolation for Latitude/LHA in sight reduction tables?
From: Gary LaPook
Date: 2008 Jul 09, 03:15 -0700
From: Gary LaPook
Date: 2008 Jul 09, 03:15 -0700
That is the same methodology and formulas used to print the "Motion of
the observer" and the "motion of the body" correction tables in H.O 249.
gl
Thomas Kleemann wrote:
--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
gl
Thomas Kleemann wrote:
It's a little late but I'll jump in here. To achive a correction for the intercept from AP to DR one can assume some simplification: Because intercepts are usually short (less than 45 nm) plane geometry is sufficiently applicable. The following formula won't change the Azimuth or move your LOP at all, only the intercept is corrected for the other position it starts from. Delta I = Delta LHA * sinAz + Delta Lat * cosAz It can be done by tables, a natural sine table has you left with two multiplications, whereas a logarithmic sine table uses sums only. Don't get confused by the term 'Delta LHA', thats the difference between your longitudes AP vs DR, expressed by the minutes you round the LHA up or down for AP. This way you spare one calculation. /Thomas P.S. I haven't looked after it, but, maybe the old traverse tables are of some use here. Greg R. schrieb:Here's something that I've wondered about for a while: Does anyone know why there aren't interpolation tables for Latitude and LHA in the sight reduction tables (as there are for Dec)? Seems like if there were, we could just use the DR position as the AP - which would also make for faster position-finding since there wouldn't be a need to plot individual APs for each of the sights. Might have something to do with the limited amount of computing power available when the tables were first created (as was discussed with the reason why Pub 229 is LHA-oriented), or maybe Latitude and LHA don't vary linearly between even degrees - but I was curious if anyone knew if there was some reason for it. -- GregR
--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---