[GRASS-dev] r.distance problem: in our out?

[Markus Neteler]

Hi,

backported to GRASS 6.2-CVS for 6.2.2.

Markus


hallo,

Dylan tested and found no error. Patch commited, r.distance has -o flag
for taking care on overlapping rasters

    jachym

On Tue, Oct 10, 2006 at 03:33:56PM +0200, Jachym Cepicky wrote:
> hallo,
> 
> On Wed, Oct 04, 2006 at 01:38:25PM +0200, Markus Neteler wrote:
> > Hi,
> > 
> > for an application I have to calculate the distance between
> > raster "objects". While this generally works, I have found
> > that r.distance happily calculates the distance even if
> > one object is within the other (say, raster pixel over
> > raster polygon in second map). I would need an indication
> > somehow that we are *in* (to ignore the distance in this
> > case).
> 
> i did not found any G_is_null(raster_map_name,x,y) or similar function.
> is there something like this?
> 
> thank you
> 
> jachym
> 
> one cell from mypixel is "surrounded" 
> > 
> > Spearfish example:
> > 
> > g.region -dp
> > 
> > # extract field #25:
> > r.mapcalc "myarea=if(fields == 25, 1,null())"
> > 
> > # this archsite falls into field 25:
> > v.extract archsites out=mypixel list=9
> > v.to.rast mypixel out=mypixel use=val val=1
> > r.distance mypixel,myarea 
> > # -> reports two distant points
> > 
> > # zoom:
> > g.region n=4926990 s=4925856 w=599850 e=601376 align=myarea
> > d.mon x0
> > d.rast myarea
> > d.vect mypixel col=blue
> > # visualize distance (d.graph give sometimes random output!):
> > r.distance mypixel,myarea | awk -F: '{print
> "move",$4,$5,"\ndraw",$6,$7}' | d.graph -m
> > 
> > # generate points from distance for easier verification:
> > r.distance mypixel,myarea | awk -F: '{print $4,"|",$5,"\n",$6,"|",$7}' |
> sed  's+ ++g' | v.in.ascii out=distance
> > d.vect distance col=yellow
> > 
> > # cleanup:
> > g.remove rast=myarea,mypixel
> > g.remove vect=mypixel,distance
> > 
> > ###
> > Problem: There is no indication that we are *within* the area. Maybe a
> flag is
> > needed to optionally suppress the result in this case?
> > Better ideas?
> > 
> > Second problem: The result seems to be underestimated by half a cell
> > since not the cell edge is taken from the raster polygon boundary 
> > but the cell center.
> > 
> > Appreciating help,
> > Markus
> 
> -- 
> Jachym Cepicky
> e-mail: jachym.cepicky at centrum.cz
> URL: http://les-ejk.cz
> GPG: http://les-ejk.cz/gnupg_public_key/jachym_cepicky-gpg_public_key.asc
> -----------------------------------------   
> OFFICE:                                     
> Department of Geoinformation Technologies 
> Zemedelska 3
> 613 00, Brno
> Czech Republick
> e-mail: xcepicky at node.mendelu.cz
> URL:    http://mapserver.mendelu.cz
> Tel.:   +420 545 134 514

-- 
Jachym Cepicky
e-mail: jachym.cepicky at centrum.cz
URL: http://les-ejk.cz
GPG: http://les-ejk.cz/gnupg_public_key/jachym_cepicky-gpg_public_key.asc
-----------------------------------------   
OFFICE:                                     
Department of Geoinformation Technologies 
Zemedelska 3
613 00, Brno
Czech Republick
e-mail: xcepicky at node.mendelu.cz
URL:    http://mapserver.mendelu.cz
Tel.:   +420 545 134 514

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