[Proj] Info on proj4 formulas

[Charles Karney]

The JHS formulas (extended to 6th order) are proj.4's etmerc projection
(e = "extended").  The 4th-order series in JHS were first given by
Krueger in 1912.  The same formulas (at 6th order) are now recommended
by NGA for UTM (see my posting of 2014-04-29).

   --Charles

On 2014-05-09 13:36, Antti Castrén wrote:
> Hi,
>
> It seems that they differ at least on Transverse Mercator. OGP
> Guidance currently recommends so called JHS formulas which are
> satisfactory within +/-40 degrees from central meridian compared to
> Snyder's +/-4 degrees. Snyder's formulas seem to be coded in proj.4
> PJ_tmerc if I have read the current version correctly.
>
> For more information read OGP document pages 48...53
>
>
> Cheers,
>
>    Antti
>
> FYI: The so called JHS formulas were actually created by prof R A
> Hirvonen and published (in Finnish) already back in 1972.
> http://en.wikipedia.org/wiki/Reino_Antero_Hirvonen
>