[Proj] Lambert projection with one or two standard parallels and proj4

[Linton Corbet]

Hello all,

I'm sure there is a gap in my understanding, but I haven't been able to
identify where it is, nor how to fill it. My issue is this:

I'm transforming lon lat coordinates into a lambert conformal conic
projection.

The lambert projection uses a single standard parallel 46.244 and the
central meridian is 17.0. And it's on a sphere, but that's not particularly
relevant here. I am using packages that use the proj4 library.

I test the transformation using linux tool cs2cs as follows:

echo "15.220483 48.437298" | cs2cs +proj=lonlat +to +proj=lcc
+lat_1=46.244 +lat_0=46.244 +lon_0=17. +a=6367470 +b=6367470 +ellps=sphere
+datum=WGS84

-131346.80 245318.16

I also understand that the one-standard parallel form is the same as the
two-standard parallel form if the two standard parallels are the same. It
is more convenient for me to give all parallels in my scripts - let proj do
the work. So I also test with:

echo "15.220483 48.437298" | cs2cs +proj=lonlat +to +proj=lcc +lat_1=46.244
+lat_2=46.244 +lat_0=46.244 +lon_0=17. +a=6367470 +b=6367470 +ellps=sphere
+datum=WGS84

-131290.66 245281.34

yet I get different results. Any ideas as to why?

And at very least, what am I doing wrong and which approach should I use?

Kind regards,
Linton Corbet
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