[GRASS-user] v.generalize issues

[Markus Metz]

On Thu, Jun 30, 2011 at 4:01 PM, Christian Guirreri
<christian at guirreri.com> wrote:
> I'm a brand new user to GIS - my goal right now is to heavily simplify Tiger
> 2010 county and distrct data, without producing gaps between boundaries.
> I've been testing this with v.generalize in grass via QuantumGIS - I've had
> tons of issues with the Grass toolbox crashing, but have narrowed down to
> using the Hermite algorithm. While it works, I'm having some bizarre issues
> with it. Apologies for the cross-post with the PostGIS mailing list.
>
> In the attached gif of California counties, from left to right, I have used
> the following tolerance values with the Hermite algorithm:
>  - original
>  - 1.0
>  - 0.08
>  - 0.01
>  - 0.00001
>
> Why do counties disappear entirely as I decrease the tolerance?
>
This problem has been fixed in GRASS 6.4 only 2 weeks ago (June 13).
Please update your GRASS version if possible.

Markus M


> In the Grass Tools I choose the v.generalize function. I choose Boundary as
> the feature type (though I've tried checking others, as well as all of them
> and it doesn't seem to change anything). Everything else is default, except
> for tolerance as notated above.
>
> When I tested this originally on only Arkansas and Mississippi, I got really
> nice results. I then tried it on the entire US and had the missing counties
> problem. So I tried only California, and still have the same issue.
>
> I've tried other algorithms, but this has so far given me the detail I want
> - of course sans counties! Any thoughts?
>
> Thanks,
>  - Chris
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