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

[GRASS GIS]

#35: Verify and uncomment Swiss datum parameters
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  Reporter:  neteler      |       Owner:  grass-dev at lists.osgeo.org
      Type:  defect       |      Status:  new                      
  Priority:  major        |   Milestone:  6.4.0                    
 Component:  default      |     Version:  unspecified              
Resolution:               |    Keywords:                           
  Platform:  Unspecified  |         Cpu:  Unspecified              
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Comment (by pkelly):

 Many thanks to swisstopo. The information is really helpful and when I
 have time to digest it I will update GRASS's handling of the Swiss datums
 appropriately.

 Probably we can include the NTv2 grid in GRASS so it is irrelevant whether
 some areas have less accuracy with the 3-parameter rather than the
 7-parameter transform. And for users who only require approx. metre-level
 accuracy, treating CH1903 as the same as CH1903+ may be adequate. But at
 least finally the difference between them is clear (I think!): CH1903 is
 the old classically triangulated datum in widespread use throughout
 Switzerland. CH1903+ is a redefinition of this datum, derived from GPS
 rather than classical triangulation. I suspect in many areas there is
 little difference between the too - perhaps the fact that there are so
 many big mountains in Switzerland caused some distortion within the old
 CH1903, and that has been removed in CH1903+? I'm just speculating though.
 It sounds like a similar situation to when the Ordnance Survey of Great
 Britain redefined their OSGB36 to be referenced to GPS - I don't have a
 figure for the biggest difference between a point in the two definitions
 of that same datum though. Their website is also quite detailed like the
 Swiss one - perhaps the information would be there if we went looking for
 it.

 @Maciek re: missing link, try
 http://www.swisstopo.admin.ch/internet/swisstopo/en/home/topics/survey/sys/refsys.parsysrelated1.2487.downloadList.82881.DownloadFile.tmp/swissprojectionen.pdf

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Ticket URL: <http://trac.osgeo.org/grass/ticket/35#comment:4>
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