[PROJ] general use of proj_factors

[Roger Oberholtzer]

On Fri, Oct 25, 2024 at 12:17 PM Javier Jimenez Shaw <j1 at jimenezshaw.com> wrote:
>
> About proj_create_crs_to_crs, I think you need the geographic as lon-lat and radians (as Kristian suggested) for the input of proj_factors(). I do not know how to get that easily.

My call to proj_factors is like this:


       PJ_FACTORS factors;
       PJ_COORD vals;

       vals.lp.lam = DegreesToRadians(point->LONGITUDE);
       vals.lp.phi = DegreesToRadians(point->LATITUDE);

       factors = proj_factors(tinfo->Meridian, vals);

where point->LONGITUDE and point->LATITUDE are the values I projected
and about which I want the meridian convergence. That part is working
fine. tinfo->Meridian is the transform I am trying to define. That
remains the issue.

My suggested code (below) does not work. So what I am trying to
discover is how, given an EPSG code, I can get the corresponding proj4
string. projinfo lists it. But discovering how it obtained it has not
been straight-forward. c++...

PJ *tmp = proj_create("EPSG:5678");
PJ_PROJ_INFO info = proj_pj_info(tmp);
PJ *used = proj_create(info.definition);
proj_destroy(tmp);

I seem to be missing a piece of the puzzle.


-- 
Roger Oberholtzer