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incorrect convergence calculation for lcc projection. #16
Reported by keesk on 22 Sep 2008 08:36 UTC
Convergence calculation for lcc seems to have an incorrect sign. The convention for convergence is:
To demonstrate this i modified proj.exe so it prints the convergence (in
When i calculate two positions along a longitude east of the origin (point E4N52 and point E4N52.1) the easting reduces when going northwards. According te the convention the convergence should be positive and not negative.
Testing with a UTM projection gives the expected results:
From the above results it seems that for utm the convergence is
From this is seems that TrueNorth = GridNorth + convergence which complies with the convention.
Last Modified by warmerdam on 22 Sep 2008 14:54 UTC
Comment by warmerdam on 22 Sep 2008 14:54 UTC
with the (current) conclusion:
I'll wait for Gerald to complete his analysis and then look to apply the same fix he does.
referenced this issue
Jul 5, 2017
My findings also confirm that LCC gives opposite sign for meridian convergence if we accept the definition: "meridian convergence on a map, at a given point, is the angle measured clockwise from
Solution is to replace the line:
fac->conv = - Q->n * lp.lam;
fac->conv = Q->n * lp.lam;