NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Looking for a mathematical ( programable ) set of rules to determine LHA
From: Peter Hakel
Date: 2010 Jan 26, 22:07 -0800
From: "aszy@mac.com" <aszy@mac.com>
To: NavList@fer3.com
Sent: Tue, January 26, 2010 7:06:30 PM
Subject: [NavList] Looking for a mathematical ( programable ) set of rules to determine LHA
From: Peter Hakel
Date: 2010 Jan 26, 22:07 -0800
I assume that you are after getting an AP that would lead to an integer LHA to enter the tables. You could add the DRP longitude to GHA and round the result to the nearest integer X. That integer will be your LHA.(*) Subtracting GHA from X will give AP longitude.
Example (all in degrees):
GHA = 10.3
DRP_Lon = -20.7
X = round( GHA + DRP_Lon ) = round(-10.4) = -10
AP_Lon = X - GHA = -10 - 10.3 = -20.3
LHA = X + 360 = 350 (since X < 0 )
(*) Note that in some cases you may need to add or subtract 360 to bring some quantities into their conventional range. In this example the extra step appears in the translation of X into LHA.
Peter Hakel
Example (all in degrees):
GHA = 10.3
DRP_Lon = -20.7
X = round( GHA + DRP_Lon ) = round(-10.4) = -10
AP_Lon = X - GHA = -10 - 10.3 = -20.3
LHA = X + 360 = 350 (since X < 0 )
(*) Note that in some cases you may need to add or subtract 360 to bring some quantities into their conventional range. In this example the extra step appears in the translation of X into LHA.
Peter Hakel
From: "aszy@mac.com" <aszy@mac.com>
To: NavList@fer3.com
Sent: Tue, January 26, 2010 7:06:30 PM
Subject: [NavList] Looking for a mathematical ( programable ) set of rules to determine LHA
Good day all. I am looking for a hard and fast set of rules to apply to a dead reckoning longitude to make an assumed-longitude, such that I will always obtain the correct LHA to enter the tables with.
I do this in my head and can 'see' the correct answer, but now I find that I need to be able to actually write this out programmatically. Any takers? TIA - Al
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