[Proj] Why is cs2cs not compensating for the difference between ellispoid and sphere?

Andrea Aime andrea.aime at geo-solutions.it
Mon Apr 6 12:25:53 EST 2015

does anybody know why when going from WGS84 to the 1924 authalic sphere
cs2cs is not compensating for the difference in flattening (and thus not
changing a bit
the latitute)?

cs2cs -v +datum=WGS84 +proj=lonlat +to +proj=lonlat  +a=6371228 +b=6371228
+units=m +no_defs
# ---- From Coordinate System ----
#Lat/long (Geodetic)
# +datum=WGS84 +proj=lonlat +ellps=WGS84 +towgs84=0,0,0
# ---- To Coordinate System ----
#Lat/long (Geodetic)
# +proj=lonlat +a=6371228 +b=6371228 +units=m +no_defs
10 10
10dE 10dN 0.000

I was expecting this behavior only when adding +nadgrids=@nul (as reported
in the
faq, http://proj.maptools.org/faq.html, which is using a similar command

What am I missing?


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Ing. Andrea Aime
Technical Lead

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Via Poggio alle Viti 1187
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