[OSRS-PROJ] cs2cs and datum shift

Roberto Vidmar rvidmar at ogs.trieste.it
Fri Aug 23 10:16:41 EDT 2002

Dear Clifford,

  thanks for your answer but now I'm even more confused. I got the 7 
parameters from a sheet issued and SOLD by IGM (istituto Geografico 
Militare) where they tell me that Abbazia Pisani is located at
phi, lambda (geographic, datum Roma40) = Norhing, Easting (Gauss-Boaga) 
= phi, lambda (geographic, WGS84) = Norhing, Easting (UTM-WGS84).
They say also that Abbazia Pisani is located at 32.71 m above sea level 
= 77.79 ellps. height.
The 7 parameters come from the same sheet
AFAIK the 7 parameters transform should bring my point from one datum to 
another, it shouldn't know anythink about geoid.

But I made another test:

cs2cs -rs +proj=latlong +datum=WGS84\
  +to +proj=latlong +ellps=intl \
  +towgs84=-85.88,-28.85,+49.67,-1.003,-2.383,-1.808,-27.82 \
  +proj=latlong +datum=WGS84 aa | \
cs2cs -rIs +proj=latlong +datum=WGS84\
  +to +proj=latlong +ellps=intl \
  +towgs84=-85.88,-28.85,+49.67,-1.003,-2.383,-1.808,-27.82 \
  +proj=latlong +datum=WGS84

where aa contains my damned Abbazia Pisani coordinates in WGS84:

45d37'01.767"N 11d51'25.843"E 77.79

...and to my surprise the output is:

45d37'1.805"N   11d51'25.842"E -276.471

I thought the output should be pretty the same of the input or... am I 
wrong again?


Roberto Vidmar 
  ___  __  __    OCEANOGRAFIA
 /  / /__ /__    GEOFISICA
/__/ /__/ __/    SPERIMENTALE
Istituto Nazionale di Oceanografia e
di Geofisica Sperimentale
34010 Sgonico (TS) ITALY

Research Group: CARS
(CArtography and Remote Sensing)

Tel. +39 040 2140 336 direct
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 E-mail: rvidmar at inogs.it

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