Re: [GRASS-dev] [GRASS GIS] #1996: r.random.cells not working correctly when min distance is < 0.1

[GRASS GIS]

#1996: r.random.cells not working correctly when min distance is < 0.1
--+
  Reporter:  pvanbosgeo   |  Owner:  grass-dev@…
  Type:  defect   | Status:  new
  Priority:  normal   |  Milestone:  7.0.7
 Component:  Raster   |Version:  svn-trunk
Resolution:   |   Keywords:  r.random.cells
   CPU:  Unspecified  |   Platform:  Unspecified
--+

Comment (by martinl):

 What is status of this issue?

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Ticket URL: 
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[GRASS-dev] [GRASS GIS] #1996: r.random.cells not working correctly when min distance is 0.1

[GRASS GIS]

#1996: r.random.cells not working correctly when min distance is  0.1
-+--
 Reporter:  pvanbosgeo   |   Owner:  grass-dev@…  
 Type:  defect   |  Status:  new  
 Priority:  normal   |   Milestone:  7.0.0
Component:  Default  | Version:  svn-trunk
 Keywords:   |Platform:  Unspecified  
  Cpu:  Unspecified  |  
-+--
 I am running r.random.cells in location/mapset with latlon with a
 resolution of 0.008333. When using a minimum distance of e.g., 0.09
 degrees, random locations / cells are selected that are closer then that
 distance, including selection of neighboring cells.

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Ticket URL: https://trac.osgeo.org/grass/ticket/1996
GRASS GIS http://grass.osgeo.org

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Re: [GRASS-dev] [GRASS GIS] #1996: r.random.cells not working correctly when min distance is 0.1

[GRASS GIS]

#1996: r.random.cells not working correctly when min distance is  0.1
+---
 Reporter:  pvanbosgeo  |   Owner:  grass-dev@…  
 Type:  defect  |  Status:  new  
 Priority:  normal  |   Milestone:  7.0.0
Component:  Raster  | Version:  svn-trunk
 Keywords:  r.random.cells  |Platform:  Unspecified  
  Cpu:  Unspecified |  
+---
Changes (by martinl):

  * keywords:  = r.random.cells
  * component:  Default = Raster


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Ticket URL: https://trac.osgeo.org/grass/ticket/1996#comment:1
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Re: [GRASS-dev] [GRASS GIS] #1996: r.random.cells not working correctly when min distance is 0.1

[GRASS GIS]

#1996: r.random.cells not working correctly when min distance is  0.1
+---
 Reporter:  pvanbosgeo  |   Owner:  grass-dev@…  
 Type:  defect  |  Status:  new  
 Priority:  normal  |   Milestone:  7.0.0
Component:  Raster  | Version:  svn-trunk
 Keywords:  r.random.cells  |Platform:  Unspecified  
  Cpu:  Unspecified |  
+---

Comment(by hamish):

 what is your ew, ns region resolution? (the module uses that)

 r.random.cells does not know that 1deg lat is not the same distance as
 1deg lon. Considering the nature of what it is doing (feeding into future
 stats) I wouldn't risk the wrong answers, I'd run it from a projected
 location instead of a lat/lon one.

 the module is smart enough to deal with ew,ns resolution (of the same
 units) being different though.


 Hamish

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Ticket URL: https://trac.osgeo.org/grass/ticket/1996#comment:2
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Re: [GRASS-dev] [GRASS GIS] #1996: r.random.cells not working correctly when min distance is 0.1

[GRASS GIS]

#1996: r.random.cells not working correctly when min distance is  0.1
+---
 Reporter:  pvanbosgeo  |   Owner:  grass-dev@…  
 Type:  defect  |  Status:  new  
 Priority:  normal  |   Milestone:  7.0.0
Component:  Raster  | Version:  svn-trunk
 Keywords:  r.random.cells  |Platform:  Unspecified  
  Cpu:  Unspecified |  
+---

Comment(by pvanbosgeo):

 The region's resolution is  0.008333. Good point about different distances
 latitudinal and longitudinal. In my specific case it doesn't really matter
 though, I just want to avoid to select any two cells that are e.g., less
 then 2 cells apart). A minimum distance of 0.09 should take care of that,
 shouldn't it. However, the resulting layer does still contain plenty of
 neighboring cells selected (see attached image).

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Ticket URL: http://trac.osgeo.org/grass/ticket/1996#comment:3
GRASS GIS http://grass.osgeo.org

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Re: [GRASS-dev] [GRASS GIS] #1996: r.random.cells not working correctly when min distance is 0.1

[GRASS GIS]

#1996: r.random.cells not working correctly when min distance is  0.1
+---
 Reporter:  pvanbosgeo  |   Owner:  grass-dev@…  
 Type:  defect  |  Status:  new  
 Priority:  normal  |   Milestone:  7.0.0
Component:  Raster  | Version:  svn-trunk
 Keywords:  r.random.cells  |Platform:  Unspecified  
  Cpu:  Unspecified |  
+---

Comment(by hamish):

 without exploring the code to closely, perhaps what is happening is that
 the random points in real x,y,z space are more than 1 cell space apart
 from each other, but at the final rasterization step they trigger filling
 adjacent cells?

 {{{
 +--+
 |   .  |
 |  |
 |  |
 +--+
 |  |
 |  |
 | .|
 +--+
 }}}


 But r.random.cells works on distance between the rows and columns, so
 perhaps that is wrong and it is comparing distance between cell centers.
 Further investigation would be needed to see at what stage the
 rasterization happens.


 Hamish

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Ticket URL: https://trac.osgeo.org/grass/ticket/1996#comment:4
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