[PROJ] Meridian convergence

[Roger Oberholtzer]

I have been using proj_factors() to get the meridian convergence for a
given point. It has been working great. We need this when projecting LiDAR
points that involve multiple rotations. The code is something 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);

       return(RadiansToDegrees(factors.meridian_convergence));

I have been using it with Sweref99 (EPSG:4326).

I have two questions:

Is proj_factors() the fastest way to get this information? A look at the
code shows that it is calculating other things as well. Is there is a
faster way? When generating point clouds, each contains 10s of millions of
points, and we generated 10s of thousands of these over a summer. Needless
to say, we are always looking for speedups.

Would this method work for all 'standard' projections? By 'standard' I mean
the typical ones used in, say, European countries. Would we need to
consider anything when extending this to something other than EPSG:4326?

-- 
Roger Oberholtzer
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