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» Online Classroom   »   » Public Discussion of Cel Nav   » Creat Circle Charts

   
Author Topic: Creat Circle Charts
Mike Buchko


 - posted April 25, 2004 06:35 AM      Profile for Mike Buchko           Edit/Delete Post 
I have been using the Great Circle Chart 17 (43rd edition revised 3/30/70) for the North Atlantic to measure some distances using the two graphing methods (lat and longs) described on the chart.
When measuring distances (1800 nM to say 3200 NM) for several different tracks by the latitude method I consistently seem to be getting answers that are in error by about 80 minutes.
When I do the same measurement using the longitude method of measurement on the chart I am within a few minutes. (Lats and longs of start and end points were plugged into the sailings online calculator to get exact distances).

Is there some error when using the latitude method as compared to the longitude method or am I just doing a poor job of it? I have very tired eyes and have pretty much given up on the latitude method because if I am doing something wrong I can't seem to figure out what it is. The thing that bothers me is that the example shown on the chart for the latitude method is pretty straight forward and seems to agree completely with the longitude method so I am guessing that I must be doing something wrong.

Mike Buchko

Mike Buchko


 - posted April 25, 2004 07:52 AM      Profile for Mike Buchko           Edit/Delete Post 
Sorry for the question I just found out I was swinging the arc from Point C insted of the point of tangency. Ignore this question.
Mike

David Burch


 - posted April 27, 2004 12:09 AM      Profile for David Burch           Edit/Delete Post 
Good. that is resolved, but you may still want to read the article we have online precision great cricle computations in the Resources/Library/Articles.

I think we have the program as a free download in the shareware/freeware section.

From: Starpath, Seattle, WA


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