[Proj] Differences in Output between proj and cs2cs

[Martin Thierer]

Hi,

while trying to understand proj (and projections in general) I'm having 
difficulties to understand the differences I get when using the cs2cs program 
to convert from Lat/Lon coordinates to Equirectangular Projection and the 
same (at least: intended to be the same) conversion done with the proj 
program:

1. With proj:

proj +proj=eqc +datum=WGS84 +lat_ts=48.8 +lon_0=9.48 +ellps=WGS84
9.48 48.8
0.00    5432391.15

2. With cs2cs:

cs2cs -v +proj=longlat +datum=WGS84 +to  +proj=eqc +datum=WGS84 +lat_ts=48.8 
+lon_0=9.48
# ---- From Coordinate System ----
#Lat/long (Geodetic)
#
# +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
# ---- To Coordinate System ----
#Equidistant Cylindrical (Plate Caree)
#       Cyl, Sph
#       lat_ts=
# +proj=eqc +datum=WGS84 +lat_ts=48.8 +lon_0=9.48 +ellps=WGS84 +towgs84=0,0,0
9.48 48.8
0.00    5411149.43 -12062.35
 
Why this difference in x the y-coordinate? And why is there a difference in 
the z-coordinate? As the WGS84 ellipsis is used for both source and target 
shouldn't the z-coordinate in the result be 0 as well?

Could someone please help me?

Thank you very much!

Bye,

Martin