[GRASS-user] circular neighborhoods?

[Carlos "Guâno" Grohmann]

Thanks for the quick answer Tom.

Carlos




On Thu, Feb 21, 2008 at 3:52 PM, Tom Russo <russo at bogodyn.org> wrote:
> On Thu, Feb 21, 2008 at 03:11:43PM -0300, we recorded a bogon-computron collision of the <carlos.grohmann at gmail.com> flavor, containing:
>
> > Yes, Eric, that is what it does for a _square_ neighborhood. I am a
>  > little confuse about the actual shape of the _circular_ neighborhood.
>  >
>  > using your examples:
>  >
>  > will a 3x3 circular neighborhood look like this:?
>  >
>  > ---o---
>  > o-X-o
>  > ---o---
>  >
>  > and a 5x5?
>  >
>  > ---o-o-o---
>  > o-o-o-o-o
>  > o-o-X-o-o
>  > o-o-o-o-o
>  > ---o-o-o---
>  >
>  >
>  > maybe now my question is more clear...
>
>  Piping in here after a quick glance at the source code...
>
>  When the "-c" option to r.neighbors is selected, a neighborhood mask of booleans
>  is created by this loop (in pseudocode):
>
>   neighborhoodDistance=neighborhoodSize/2 (in integer math)
>   for (i=0; i<neigborhoodSize; i++)
>     for (j=0; j<neighborhoodSize; j++)
>        mask[i][k]= ( (i-neighborhoodDistance)^2 + (j-neighborhoodDistance)^2 <= (neighborhoodDistance)^2
>
>  So in a 3x3 example, neighborhoodSize=3, neighborhoodDistance=1, and your
>  first diagram has "o"s where the mask is true.  The corners of the square
>  wouldn't be in the mask (as in Eric's 3x3), because those points would have
>  the left hand side of the inequality equal to 2, making the mask false.
>
>  I haven't actually *tried* the code, but that is what the block of code in
>  gather.c for circular neighborhoods says it should be doing.
>
>
>
>  > > >I was thinking about the circular neighborhoods that r.neighbors use.
>  > >  >How exactly are they shaped? I mean, in a 3x3 window, does the
>  > >  >circular one looks like a cross? and then it start to look more like a
>  > >  >circle as the size increases?
>  > >
>  > >  As far as I understand it,
>  > >
>  > >  A 3x3 window would look like this:
>  > >
>  > >  o-o-o
>  > >  o-X-o
>  > >  o-o-o
>  > >
>  > >  Where the 'X' is the current cell being processed. Similarly, a 5X5 window
>  > >  would look like this:
>  > >
>  > >  o-o-o-o-o
>  > >  o-o-o-o-o
>  > >  o-o-X-o-o
>  > >  o-o-o-o-o
>  > >  o-o-o-o-o
>  > >
>  > >  r.neighbors will perform calculations on all the cells I've marked 'o' and and
>  > >  assign the output value to 'X', according to whatever method has been chosen
>  > >  (i.e., average, median, min, max, etc.).
>  > >
>  > >  ~ Eric.
>  > >
>  >
>  >
>  >
>  > --
>  > +-----------------------------------------------------------+
>  >  Carlos Henrique Grohmann - Guano
>  >  Geologist M.Sc - Doctorate Student at IGc-USP - Brazil
>  > Linux User #89721 - carlos dot grohmann at gmail dot com
>  > +-----------------------------------------------------------+
>  > _________________
>  > "Good morning, doctors. I have taken the liberty of removing Windows
>  > 95 from my hard drive."
>  > --The winning entry in a "What were HAL's first words" contest judged
>  > by 2001: A SPACE ODYSSEY creator Arthur C. Clarke
>  >
>  > Can't stop the signal.
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>
>  --
>  Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
>  Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 http://kevan.org/brain.cgi?DDTNM
>  "And, isn't sanity really just a one-trick pony anyway? I mean all you get is
>   one trick, rational thinking, but when you're good and crazy, oooh, oooh,
>   oooh, the sky is the limit!"  --- The Tick
>



-- 
+-----------------------------------------------------------+
 Carlos Henrique Grohmann - Guano
 Geologist M.Sc - Doctorate Student at IGc-USP - Brazil
Linux User #89721 - carlos dot grohmann at gmail dot com
+-----------------------------------------------------------+
_________________
"Good morning, doctors. I have taken the liberty of removing Windows
95 from my hard drive."
--The winning entry in a "What were HAL's first words" contest judged
by 2001: A SPACE ODYSSEY creator Arthur C. Clarke

Can't stop the signal.