[postgis-users] Recommendations with GRASS v.generalize() on Tiger Data

[Christian Guirreri]

Narrowed down some test to using the "Hermite" algorithm, but I'm having
some bizarre issues with it.

In the attached gif of California counties from Tiger data, from left to
right, I have the following tolerance values:
 - original
 - 1.0
 - 0.08
 - 0.01
 - 0.00001

Why do counties disappear entirely as I decrease the tolerance?

Setup is QuantumGIS with GRASS. In the Grass Tools I choose the v.generalize
function. I choose Boundary as the feature type (though I've tried checking
others and it doesn't seem to change anything). Everything else is default,
except for tolerance as notated above.

When I tested this original 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 what I want. Any
thoughts?
 - Chris


On Wed, Jun 29, 2011 at 5:10 PM, Christian Guirreri
<christian at guirreri.com>wrote:

> I'm currently going through the GRASS v.generalize() function's various
> parameters in QuantumGIS. There's so many options, I'm not entirely sure
> what's best. Has anyone tried this on Tiger 2010 counties or district data?
> Any particular recommendations?
>
> What's most important to me, as mentioned in a previous thread, is that
> there are no gaps between counties/districts in a similar fashion to
> MapShaper.
>
> Thanks,
>  - Chris
>
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