[GRASS-dev] [GRASS GIS] #1948: r.fillnulls / v.surf.rst: use of segmax and npmin disarranged

[GRASS GIS]

#1948: r.fillnulls / v.surf.rst: use of segmax and npmin disarranged
------------------------------------+---------------------------------------
 Reporter:  sbl                     |       Owner:  grass-dev@…              
     Type:  defect                  |      Status:  new                      
 Priority:  normal                  |   Milestone:  7.0.0                    
Component:  Raster                  |     Version:  svn-trunk                
 Keywords:  v.surf.rst,r.fillnulls  |    Platform:  Unspecified              
      Cpu:  x86-64                  |  
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 After some speed-up r.fillnulls still feels quite slow on big rasters
 ([http://trac.osgeo.org/grass/ticket/1938]).

 On further investigation in particular the following waring message
 indicated some confusion in the npmin and segmax settings in r.fillnulls
 and/or v.surf.rst:

 {{{
 Interpolating 40 points[[BR]]
 (...)[[BR]]
 WARNING: There are less than 80 points for interpolation.[[BR]]
 No segmentation is necessary, to run the program faster set segmax=80 (see
 manual)
 }}}

 In r.fillnulls, if number of points is below 600, then both segmax and
 npmin are set to "pointsnumber". So, from r.fillnulls segmax was set to 40
 (and not 80, like the warning message indicates...). Then I tested in
 v.surf.rst with a hole with 1033 existing data points on the edge with the
 following result:

 If I set
 segmax = 1033
 npmin = 1033
  I get the following Warning message:
 {{{
 WARNING: There are less than 2066 points for interpolation.[[BR]]
 No segmentation is necessary, to run the program faster set segmax=2066
 (see manual)
 }}}
 Interpolation is done within 6 seconds.


 I get the same message if I set:
 segmax = 517
 npmin = 1033
 But now processing takes now 16 seconds...

 The warning message above changes to

 {{{
 WARNING: There are less than 1034 points for interpolation.[[BR]]
 No segmentation is necessary, to run the program faster set segmax=1034
 (see manual)
 }}}
  when I set:
 segmax = 1033
 npmin = 517
 Strange that it is possible because in the GUI it says npmin has to be
 greater than segmax...
 But processing time is down on 6 secs again...

 With:
 segmax = 1033
 npmin = 516.
 I get the expected error message, that npmin has to greater than segmax.

 Finally, I set segmax and npmin to the "default" in r.fillnulls for holes
 with pointnumber >= 600:
  segmax = 100
 npmin = 300
 Now processing takes 55 seconds!!!
 This is especially confusing because during the tests with npmin = 1033 I
 got the following warning message in addition:
 {{{
 WARNING: The computation will last too long - lower npmin is suggested"
 }}}
 But actually, processing was nearly 10 times faster then with npmin=300!

-- 
Ticket URL: <http://trac.osgeo.org/grass/ticket/1948>
GRASS GIS <http://grass.osgeo.org>