[GRASS-user] Presence/Absence error

[Hamish]

Joel wrote:
> > Thanks guys! I had some vaque idea how to do it - but the v.to.ascii
> > command line is really fast - so just what I need.
> >
> > However one problem is using v.to.rast:
> >
> > http://static.flickr.com/93/242928408_189e335e04_o.png
> >
> > This is result of:
> > create a raster map1 from v.to.rast
> > place nulls into map2 where map1 cells are not null (basically
> > subtracting the vector points from map2)
> >
> > As you can see in the screenshot, some of the points and the raster
> > cells of map1 don't line up. Ignore the null cells at the bottom of
> > the map as it is near a coast line and have nothing to do with the
> > vector.
> >
> > Any idea why this is? and how to get around it?
..
> Hi again, turns out I can't reproduce this error - thus it is most
> likely that occured from me doing something strange.


My guess is that the region bounds/resolution changed after the
v.to.rast type=points step, so the cells were being resampled on
display.

be sure to do:

g.region rast=target_map

before v.to.rast.


this also happens if your region is like: n=5000175 s=5000025 w=1000175
e=1000025 and your res=50. After zoom the region aligns to whole "00"
and all cells are resampled with 1/2 a cell error in both horiz and
vert.



Hamish