On Thu, Jun 30, 2011 at 7:49 PM, Christian Guirreri <[email protected]> wrote: > I suppose my other question is if anyone has any recommendations concerning > v.generalize as it applies specifically to tiger data - I'm doing all of US. > Lots of settings and tests and its a bit overwhelming for a newbie. > For simplification (vertex reduction), Douglas-Peucker is generally a good choice, it's relatively simple and commonly used.
For smoothing, Chaiken's Algorithm and Hermite Interpolation should produce quite different results, apart from being a matter of taste, it depends on what kind of modifications are allowed. Markus M > On Jun 30, 2011 11:33 AM, "Christian Guirreri" <[email protected]> > wrote: >> Success! Thanks for making this easy for the total noob that I am. >> >> On Thu, Jun 30, 2011 at 11:04 AM, Markus Metz < >> [email protected]> wrote: >> >>> On Thu, Jun 30, 2011 at 4:47 PM, Christian Guirreri >>> <[email protected]> wrote: >>> > I'm on GRASS 6.4.1. QGIS 1.7.0 >>> > >>> In this version, v.generalize is still broken. You would need a recent >>> version of GRASS 6.4.2. For Windows, you can get a recent version >>> here: >>> >>> http://wingrass.fsv.cvut.cz/grass64/ >>> >>> Markus M >>> >>> >>> > On Thu, Jun 30, 2011 at 10:18 AM, Markus Metz >>> > <[email protected]> wrote: >>> >> >>> >> On Thu, Jun 30, 2011 at 4:01 PM, Christian Guirreri >>> >> <[email protected]> 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 >>> >> > _______________________________________________ >>> >> > grass-user mailing list >>> >> > [email protected] >>> >> > http://lists.osgeo.org/mailman/listinfo/grass-user >>> >> > >>> >> > >>> > >>> > >>> > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
