[GRASS-dev] Re: [GRASS GIS] #163: g.transform no longer calculating error for 2nd order transformation

[GRASS GIS]

#163: g.transform no longer calculating error for 2nd order transformation
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  Reporter:  cmbarton  |       Owner:  grass-dev at lists.osgeo.org
      Type:  defect    |      Status:  reopened                 
  Priority:  major     |   Milestone:  6.4.0                    
 Component:  default   |     Version:  svn-develbranch6         
Resolution:            |    Keywords:  g.transform georectify   
  Platform:  All       |         Cpu:  Unspecified              
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Changes (by hamish):

  * status:  closed => reopened
  * resolution:  fixed =>

Comment:

 > It turns out that 2nd order transformation need MORE than 6 points, not
 6 points
 > or more

 Not according to the i.rectify man page,

 "The number of control points required for a selected order of
 transformation (represented by n) is ((n + 1) * (n + 2) / 2) or 3, 6, and
 10 respectively."

 And imagery/i.vpoints/analyze.c's compute_transformation() which leads to
 imagery/i.vpoints/crs.c's calccoef() function agrees. n >= 6.

 The same code is reused by g.transform, I assume they are identical after
 re-indent.
 no idea about what the needs of backtransforming are. I assume they are
 symetric with a forward transform.

 No idea if any of this matters to the status this bug. Reopening as the
 reason for closing it is invalid and the interactive georectify modules
 now need to be reverted.


 Hamish

-- 
Ticket URL: <http://trac.osgeo.org/grass/ticket/163#comment:3>
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