Convergency & CA

 

Convergency : It is the inclination between two meridians at a given latitude. It is Maximum at poles and ‘0’ at equator  . It varies a function of SIN of mean latitude.

Convergency = d.Longitude X Sin Mean latitude

X = A2 – A1

Conversion Angle : Angular diffrence between Rhumb Line (RL) & Great Circle (GC) at a given latitude is called Conversion Angle.

CA = Y

X = A2 – A1

 if Angular difference of GC bearings is = 180*  then its Equator,

 if Angular difference of GC bearings is  > 180*  then its Northern Hemisphere,

 if Angular difference of GC bearings is  <180*  then its Southern Hemisphere,

Ex: Great circle bearing of A from B is 262*. Great circle bearing of B from A is 075*, Find Rhumb line Bearing of B from A.

Ans:

Angular Difference = 262*-075* = 187*

hence in Northern Hemisphere as difference is > 180*

Covergency = 187*-180* = 7*

CA = 7/2 = 3.5* or 4*

Ex: A & B are on parallel of latitude of 30*. Great circle bearing of A from B is 096*. Longitude of B is 4*W. Find Longitude of A.

Ans:

CA =(d.long x sin Lat)/2

6=(X x Sin 30)/2

X=24*

hence longitude = 20* E


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