[Talk-us] What to do with unnamed NHD streams

Dale Puch dale.puch at gmail.com
Mon Oct 29 04:09:40 GMT 2012


Simplification to 2.5M seems a reasonable decision to me, possibly even up
to 5M if it results in a significant reduction in data volume.

Dropping the two FCodes sounds like a reasonable idea.  They can always be
added at a later date if desired, and imported at other levels of
simplification at that time.

Dale

On Sun, Oct 28, 2012 at 11:58 PM, Michal Migurski <mike at teczno.com> wrote:

> On Oct 28, 2012, at 8:51 PM, Paul Norman wrote:
>
> > Background: I'm working on converting NHD to .osm format
> >
> > …
> >
> > 2. Some ways are very over-noded. The NHD accuracy standard is <12m error
> > 90% of the time. Running a 1m simplify in JOSM reduces the number of
> nodes
> > to 25%-50% of what it was before. Like everything with the NHD, this
> varies
> > from region to region. I'm thinking a 2.5m simplification would be best -
> > it's 1/5th of the accuracy standard. Of course, running a simplification
> on
> > a dataset this large is a challenge in itself.
>
> Does it all come in shapefile form? The simplification would be a
> relatively easy (though time-consuming) task for PostGIS on a server with
> sufficient storage, outputting new shapefiles for ogr2osm. I can help with
> this using one of our office servers that we use for such tasks.
>
>
> > 3. A lot of NHD is very minor streams "only of use to hydrologists."
> There
> > are streams that you would be hard pressed to locate if you were there in
> > person and in some cases they do not exist anymore.
> >
> > A sensible solution in any NHD translation may be to drop any FCode 46003
> > (intermittent) streams without a name. It may also be worth dropping
> FCode
> > 46006 (perennial) streams without a name.
>
> Can these be simplified to a lower level of accuracy?
>
> -mike.
>
> ----------------------------------------------------------------
> michal migurski- mike at stamen.com
>                  415.558.1610
>
>
>
>
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-- 
Dale Puch
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