[GRASS-user] Question about v.to.rast

[Thomas Adams]

Sotiris,

Thank you for your reply -- I'll file your suggestion away for future
issues. What I ended up doing was to add a column to all my messy polygons
using v.db.addcolumn; then to make the value for that field the same for
each polygon; then use v.dissolve, identifying that new column as the Name
of attribute column used to dissolve common boundaries. The resulting
vector map had an appropriate number of polygons. This ended up working
very well.

Cheers!
Tom


On Sat, Jun 21, 2014 at 3:02 PM, S. Koukoulas (listes) <
sotkouklistes at gmail.com> wrote:

>  This is a late reply, but you might still find it useful.
>
> You can get rid of single (or multiple) isolated pixels  by cleaning the
> raster with the following commands:
>
> r. reclass.area
> r.neighbors (with the selection option - appears only in version 7).
>
> The idea is to reclassify your raster using the area of a single or
> multiple isolated pixels ( eg. estimate what is the area of a single pixel
> in ha and use it to reclassify your raster), producing a map that will
> exclude the pixels selected below this area threshold. You will end up with
> a raster with nulls in place of the rejected pixels.
>
> Then you can use the r.neighbors to replace these nulls (and only these,
> if you use the selection option) with the mode (if it is an
> integer/categorical raster otherwise use the appropriate statistic) of the
> pixels values in the specified neighborhood. This is done by using the
> raster resulted from the r. reclass.area in the selection option and the
> original raster in the input.  You will end up with a much more "clean"
> raster to convert  to vector.
>
> best regards,
> sotiris
>
>
>
>
>
> On 06/16/2014 02:47 PM, Thomas Adams wrote:
>
> All:
>
>  I have used r.lake to simulate flood inundation in an urban area -- the
> raster looks great! What I want to do (and have done) is to use r.to.vect,
> export the vector as a KML (which works), bring the simulated flood
> inundation map KMLs into GoogleEarth and create some animations from the
> simulated inundation, including showing rising flood levels inundating the
> city streets in 3D.
>
>  I can basically do all this, except that the r.to.vect conversion
> creates a gazillion boxes that are the size of the raster pixels -- I don't
> want all the tiny boxes. What I want, is just a single (albeit, complex)
> polygon showing the flooded areas. v.dissolve will remove the boundaries of
> adjacent boxes if their cat or attributes are the same -- is this the way
> to go, namely, make all the cats or attribute values the same and then use
> v.dissolve?
>
>  Or, is there is there a better way to do what I'm attempting to do? That
> is, is it best to keep the individual small vector boxes for reasons I'm
> not considering?
>
>  Thank you,
> Tom
>
>  --
>
>
>
> _______________________________________________
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>
>


-- 
Thomas E Adams, III
718 McBurney Drive
Lebanon, OH 45036

1 (513) 739-9512 (cell)
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