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Changes between Initial Version and Version 1 of Ticket #16

Timestamp:

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

Author:

warmerdam

Comment:

This is related to the thread:

http://lists.maptools.org/pipermail/proj/2008-September/003804.html

with the (current) conclusion:

http://lists.maptools.org/pipermail/proj/2008-September/003821.html

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

Ticket #16
- Property cc evenden added
- Property status changed from new to assigned

initial	v1
1	1
2	2	Convergence calculation for lcc seems to have an incorrect sign. The convention for convergence is:
3
	3	{{{
4	4	meridian convergence = bearing of grid north (measured clockwise from true north)
5	5
6	6	so: true bearing = grid bearing + convergence
7
	7	}}}
8	8	To demonstrate this i modified proj.exe so it prints the convergence (in
9	9	deg) at the end of the line when using the -S flag:
10	10
11	11
12
	12	{{{
13	13	C:\proj-4.6.1\src>proj -vS +proj=lcc +datum=WGS84 +lat_0=52 +lon_0=3
14	14	+lat_1=50 +lat_2=54
…	…
27	27	68481.15 11591.10 <0.999393 0.999393 0.998787 0.000434814
28	28	0.999397 0.99939 -0.788173>
29
	29	}}}
30	30
31	31	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.
32	32
33	33	Testing with a UTM projection gives the expected results:
34
	34	{{{
35	35	C:\proj-4.6.1\src>proj -vS +proj=utm +datum=WGS84 +lon_0=3
36	36	#Universal Transverse Mercator (UTM)
…	…
47	47	568496.62 5772632.28 <0.999658 0.999658 0.999315 0 0.999658
48	48	0.999658 0.789115>
49
	49	}}}
50	50	From the above results it seems that for utm the convergence is
51	51	negative when west and positive when east of lon_0.