[Proj] Why use pj_inv() and pj_fwd() instead of pj_transform() ?

Gerald I. Evenden geraldi.evenden at gmail.com
Sun Jun 3 17:10:14 EDT 2007

On Sunday 03 June 2007 3:19 pm, fabrice martin wrote:
> >The principle reason is that a prime meridian can easily be compensated
> > for with simple modification of the central meridian (+lon_0).
> In
> that case, shouldn't EPSG definitions be modified, in order to use
> +lon_0 instead of +pm ? For example, French Lambert projections are
> defined with "+lon_0=0 +pm=paris". Wouldn't it be better to use simply
> "+lon_0=2.33..." ? It would enable pj_inv, pj_fw and pj_transform to
> return similar results.

I personally do not favor a change in either proj/libproj library nor EPSG but 
would suggest that the software using the proj/libproj libraries compensate 
for the adjustment.  Admittedly, my program proj did not prove for prime 
meridians but it was originally designed to be an elementary mechanism to use 
the projection library and in the era that I put the material together I and 
the group using it were total ignorant of varying prime meridians.

As an aside, the fact that proj/libproj provides for false easting and 
northing somewhat compromises my argument for the current handling of the 
prime meridian as these corrections are easily handled external to the 
library.  But the difference here was the UTM projection which is defined as 
part of the library and requires hardwired northing/easting values.

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

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