[Proj] True North Angle

[Gerald I. Evenden]

On Monday 23 June 2008 11:52 am, Hersman, William wrote:
> Hello,
>
> Does anyone know the formula to calculate the deviation angle between
> true north and Universal Transverse Mercator grid north?  Thanks.
>
> Willy Hersman

How accurate to you want?  lproj -V does a reasonable job for convergence for 
*any* projection.

lproj +proj=utm +zone=31 +ellps=WGS84 -V
#Universal Transverse Mercator (UTM)
#       Cyl, Sph
#       zone= south
# +proj=utm +zone=31 +ellps=WGS84
#Final Earth figure: ellipsoid
#  Major axis (a): 6378137.000
#  1/flattening: 298.257224
#  squared eccentricity: 0.006694379990
2 45                              <----------------------------- entered value
Longitude: 2dE [ 2 ]
Latitude:  45dN [ 45 ]
Easting (x):   421184.70
Northing (y):  4983436.77
Meridian scale (h) : 0.99967638  ( -0.03236 % error )
Parallel scale (k) : 0.99967638  ( -0.03236 % error )
Areal scale (s):     0.99935287  ( -0.06471 % error )
Angular distortion (w): 0.000
Meridian/Parallel angle: 90.00000
Convergence : -0d42'25.715" [ -0.70714305 ]                 <-------
Max-min (Tissot axis a-b) scale error: 0.99968 0.99968

-- 
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939)  British psychologist