[GRASS-dev] Re: [GRASS GIS] #35: Verify and uncomment Swiss datum parameters

[Massimiliano Cannata]

maybe this can help (CH1903 to WGS84):
http://www.swisstopo.admin.ch/internet/swisstopo/en/home/products/software/products/skripts.html

GRASS GIS wrote:
> #35: Verify and uncomment Swiss datum parameters
> ---------------------------------+------------------------------------------
>   Reporter:  neteler             |       Owner:  grass-dev at lists.osgeo.org
>       Type:  defect              |      Status:  closed                   
>   Priority:  major               |   Milestone:  6.4.0                    
>  Component:  Projections/Datums  |     Version:  unspecified              
> Resolution:  fixed               |    Keywords:  CH1903, Swiss            
>   Platform:  Unspecified         |         Cpu:  Unspecified              
> ---------------------------------+------------------------------------------
> Comment (by pkelly):
>
>  My understanding: ETRS89 is fixed to the European/Eurasian plate. It was
>  the same as WGS84 in 1989 and since then has been drifting by a centimetre
>  or two per year. But the ellipsoid is the same (well, given the
>  GRS80/WGS84 difference which is miniscule). Presumably it's quite easy to
>  compensate for the drift between ETRS89 and WGS84 when interpreting GPS
>  co-ordinates (do some GPS receivers do this? I have no idea), and then
>  after that it is simple to apply a localised country datum transformation
>  grid or parameters, which don't change over time.
>
>  The interesting thing about CH1903+ is that it is only compatible with
>  ETRS89 in the sense that a simple rotation brings it into alignment
>  (3-parameter transform) and there is negligible distortion. But to convert
>  from CH1903 to ETRS89 you first need to apply the gridshift transform to
>  remove the localised surveying distortions and get to CH1903+, and then
>  apply the rotation separately. However the structure of PROJ.4 only allows
>  for the concept of a gridshift file converting to WGS84.
>
>   
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>
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-- 

Dr. Eng. Massimiliano Cannata
Responsabile Area Geomatica
Istituto Scienze della Terra
Scuola Universitaria Professionale della Svizzera Italiana
Via Trevano, c.p. 72
CH-6952 Canobbio-Lugano
Tel: +41 (0)58 666 62 14
Fax +41 (0)58 666 62 09