[GRASS-user] Mask creation from sporadic data v.hull

[Dylan Beaudette]

Hi,

I have solved this problem in the past with a combination of g.region,
v.to.rast, and r.grow.

For example, if you import your points in as a vector-- convert to
raster, increase the cell size, and grow out a couple of cells. If you
are bringing in your lidar data with r.in.xyz, then it is already a
raster, and you can adjust the resolution and "grow" accordingly. Make
sense?

Cheers,
Dylan

On Fri, Dec 18, 2009 at 4:04 AM, John Tate <john.tate at ntlworld.com> wrote:
> Hi all,
>
> For a while now I have been trying to make an accurate mask for LiDAR points.
> As I am working with 1m resolution data I want the mask to be accurate (no
> more than 1m around the edge of the points/flight area).
>
> The data is wavy around the edges, due to a windy flight when the data was
> collected, so v.hull ignores the waves and joins the crests, adding vast NULL
> areas to the mask. Also, there are up to 10m holes within the individual
> swaths.
>
> r.in.xyz at 5m resolution has given me the best results so far as final
> accuracy masks, but not for the processing as I want holes within the data
> filled with v.surf.rst.
>
> I have looked at v.delaunay and v.voronoi too, but both need topology built
> and don't have similar outputs to v.hull regarding vast NULL areas. This is ok
> for 1km tiles, but I want to process each swath separately (study on swath
> accuracy) and these can be c.5million points each.
>
> Does anyone know if there is way to do this accurately without manually
> digitizing? Have I missed something in the book/manual?
>
> Cheers
>
> John
>
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