[OSRS-PROJ] cs2cs and datum shift]

[Roberto Vidmar]

-------- Original Message --------
Subject: Re: [OSRS-PROJ] cs2cs and datum shift
Date: Mon, 26 Aug 2002 10:41:14 +0200
From: Roberto Vidmar <rvidmar at inogs.it>
To: Clifford J Mugnier <cjmce at lsu.edu>
References: <OF625FF421.F9D24C30-ON86256C1E.005C2142 at lsu.edu>



Hi Clifford,

Clifford J Mugnier wrote:

>Roberto,
>
>For the inverse, you have to change the sign of the components for the
>translations AND for the rotations.  The scale factor is one minus the
>reciprocal.  Once you do that, then you should get sub-millimeter precision
>in duplicating what you started with.
>
I agree.

>Also, note that there are two different conventions for the sense of the
>rotations.  The correct way is that used by NIMA as defining the WGS84
>Datum (Counter-clockwise rotations as in vector mechanics and physics).
>The ITRF people in Paris confused the math and they use clockwise
>rotations.  What Firenze uses depends on whether they use American GPS
>software or French/Swiss software ...
>
I know.

>So when you diddle with the parameters you were sold; you SHOULD have been
>provided at least ONE test point to validate the math model you choose to
>use (PROJ4), versus what the results should be.
>
This is what I'm trying to validate, but I have no luck yet...

>  The parameters are
>intended to be used from Latitude, Longitude, ellipsoid heights to
>Latitude, Longitude, ellipsoid heights.
>
The parameters I have should bring me from local datum (Roma40) that is 
referred to heights above sea level to WGS84 that does know nothing 
about geoid (AFAIK).

>  The relation with elevation is dependant on geoid models (at both ends of the transform).
>
>Make sense?  I hope so; if not, continue asking questions.
>
The geoid stuff is quite complicated and I know that many people are 
deep inside this matter. From my point of view if I run a program with 
some input and then again requiring the reverse transform I should 
return to the same starting point. So either I called the program with 
wrong parameters or it is buggy :-)

Now forget Abbazia Pisani (near Padua by the way..) and try this:

cs2cs +proj=latlong +datum=WGS84\
  +to \
  +proj=latlong +ellps=intl \
  +towgs84=10,20,30,1,2,3,44 \
  bb | \
cs2cs +proj=latlong +ellps=intl\
  +towgs84=-10,-20,-30,-1,-2,-3,-44 \
  +to \
  +proj=latlong +datum=WGS84


cs2cs +proj=latlong +datum=WGS84\
  +to \
  +proj=latlong +ellps=intl \
  +towgs84=10,20,30,1,2,3,44 \
  bb | \
cs2cs -I +proj=latlong +datum=WGS84\
  +to \
  +proj=latlong +ellps=intl  \
  +towgs84=10,20,30,1,2,3,44

The bb file is:
11 45 77

My output is:

10d59'55.09"E   45d0'2.796"N 15.661
11dE    44d59'59.939"N 637.364

So:
1st:) The two outputs are different.
2nd:) Both are wrong.


Maybe I did not understand the syntax or my cs2cs is broken...


Any hints?

Roberto

------------------------------------
                                                             
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
------------------------------------




-- 
------------------------------------
                                                             
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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