[OSRS-PROJ] cs2cs and datum shift

[Roberto Vidmar]

Hi to all,

  this is my first experience with cs2cs so please be patient. I'm 
trying to shift coordinates between two different datums: wgs84 and 
Roma40 using a 7 parameter transformation.

cs2cs -vErs +proj=latlong +datum=WGS84 \
  +to +proj=latlong +ellps=intl\
  +towgs84=-85.88,-28.85,+49.67,-1.003,-2.383,-1.808,+27.82 \
   ap

The ap file is this:

# Abbazia Pisani
45d37'01.767"N 11d51'25.843"E 77.79

My output (Linux RH 7.3) is this:

# ---- From Coordinate System ----
#Lat/long (Geodetic)
#
# +proj=latlong +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
# ---- To Coordinate System ----
#Lat/long (Geodetic)
#
# +proj=latlong +ellps=intl
# +towgs84=-85.88,-28.85,+49.67,-1.003,-2.383,-1.808,+27.82
#--- following specified but NOT used
# +ellps=WGS84
# Abbazia Pisani
45d37'01.767"N 11d51'25.843"E 77.79     45d36'59.373"N  11d51'26.646"E 77.740


The 7 parameters I have are:
Tx:  85.88
Ty:  28.85
Tz: -49.67
Rx: -1.003"
Ry: -2.383"
Rz: -1.808"
K: 27.82

The shifted lat/lon pair are quite right, the point should be at 45d36'59.372"N (error 0.001") and 
-00d35'41.752" (Roma40 datum counts longitude from Monte Mario, 12d27'08.400"E =:-). Subtrating cs2cs output from Monte Mario longitude I get 0d35'41.750" (error 0.010", strange) but the real problem is height: 77.79 is the ellipsoidal height over WGS84 and the above sea level height of my point, Abbazia Pisani, is 32.71 m.

WHERE AM I WRONG?

I played a lot with the signs of the 7 parameters and this is the closest result I get. Does anybody else have problems like mine with datum shifts?

Thanks for your help and for the big job you have already done.

Roberto Vidmar

-- 
------------------------------------
                                                             
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
Tel. +39 040 2140 1  operator

 E-mail: rvidmar at inogs.it
------------------------------------


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