[GRASS5] Re: [GRASSLIST:2585] Re: v.to.rast aggressiveness

[Radim Blazek]

On Sunday 11 April 2004 10:48, Hamish wrote:
> On Fri, 13 Feb 2004 01:51:56 +1300 Hamish wrote:
>   http://grass.itc.it/pipermail/grassuser/2004-February/024709.html
>
> > > I'm noticing v.to.rast is rather aggressive -- (all versions
> > > 5.0,5.3,5.7)
> > >
> > > It will change many raster cells with only a little bit of vector
> > > line in it to a hit, rather than checking which side of the cell's
> > > centroid the area is on..?
> > >
> > > This has bad implications if you want to create masks covering areas
> > > both one side or the other, as it will always bias towards the side
> > > of the area vs. the negative. (say in/out of a lake's shoreline)
>
> Glynn wrote:
> > I find that rather odd, as G_plot_polygon() appears to shrink the
> > polygon which it is given.
> >
> > AFAICT, much of src/libes/gis.c is bogus; it should probably be using
> > floor(x + 0.5) consistently. However, given my experience from
> > XDRIVER[1], I'm reluctant to try to fix it, as there is probably code
> > which relies upon the existing behaviour.
> >
> > [1] XDRIVER, libraster, libdisplay and various d.* programs had a
> > number of +1/-1 "fudge" factors, which mostly cancelled each other
> > out. Once I fixed one, I had to go back up the chain and fix anything
> > which was relying upon the old behaviour.
>
> I'm having another try at this and it appears the problem goes away if I
> export the vector file to 5.3 (& run v.alabel and v.support). This
> solves my immediate problem.
>
> I'm not sure at this point what I was doing to make it show up in 5.0 &
> 5.3 before or if I was mistaken or something else is different now.
> Maybe the date had something to do with it.
>
> Trying with 5.7 from last week still produces bad results.
>
> see attached before & after pics. v2rast_1.png is using 5.7's v.to.rast,
> v2rast_3.png is using 5.3's version.
>
> Can someone confirm? Is this a 5.7 vector bug?

Are you sure the boundary is not used? If you want only the area, 
the boundary must not have a category of the field used in v.to.rast.

Radim