# Changes between Initial Version and Version 1 of Ticket #16

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Timestamp:
09/22/08 07:54:35 (5 years ago)
Comment:

This is related to the thread:

with the (current) conclusion:

I'll wait for Gerald to complete his analysis and then look to apply the same fix he does.

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• ## Ticket #16

• Property status changed from new to assigned
• ## Ticket #16 – description

initial v1
11
22Convergence calculation for lcc seems to have an incorrect sign. The convention for convergence is:
3
3{{{
44  meridian convergence = bearing of grid north (measured clockwise from true north)
55
66  so: true bearing = grid bearing + convergence
7
7}}}
88To demonstrate this i modified proj.exe so it prints the convergence (in
99deg) at the end of the line when using the -S flag:
1010
1111
12
12{{{
1313C:\proj-4.6.1\src>proj -vS +proj=lcc +datum=WGS84 +lat_0=52 +lon_0=3
1414+lat_1=50 +lat_2=54

272768481.15 11591.10 <0.999393 0.999393 0.998787 0.000434814
28280.999397 0.99939 -0.788173>
29
29}}}
3030
3131When 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.
3232
3333Testing with a UTM projection gives the expected results:
34
34{{{
3535C:\proj-4.6.1\src>proj -vS +proj=utm +datum=WGS84 +lon_0=3
3636#Universal Transverse Mercator (UTM)

4747568496.62 5772632.28 <0.999658 0.999658 0.999315 0 0.999658
48480.999658 0.789115>
49
49}}}
5050 From the above results it seems that for utm the convergence is
5151negative when west and positive when east of lon_0.