[Talk-us] NHD data import question

[Ian Dees]

On Thu, Apr 28, 2011 at 8:08 AM, James Umbanhowar <jumbanho at gmail.com>wrote:

> On Thursday 28 April 2011 08:53:56 Ben Supnik wrote:
> > Hi Ian,
> >
> > I should be able to convert the NHD data sometime in the next week or
> > so.  Also, if/when you want the original data, let me know.
> >
> > For the conversion, do we want medium or high resolution?
> >
> > Re: the import status map, I don't know how to make an actual map from
> > them....short of simply providing a KML file and saying "go look on
> > Google Earth", what formats are most useful for making an overlay status
> > map?  (I could do that conversion and hand it off to someone.)
> >
> > cheers
> > ben
> >
>
> I've been checking some of the imported data and my general feel is that it
> is
> overdigitized.  I don't know if medium versus high reflects just the
> quality or
> the amount of digitization.  That would be something to check.  One could
> also
> just run some sort of simplification algorithm on all the data.
>

I haven't seen any excess digitization, but I have seen incorrect data
(stream networks completely missing from aerial imagery and vice versa). I
suppose we could do some light simplification on the more complicated
waterbodies.


>
> Also, are the plans to make one file for each subbasin or one file per
> attribute
> (flowline, waterbody etc...).  With one file, one can remove all the
> duplicate
> nodes before uploading.
>

In the past it was file per datatype because all of the tools work with one
shapefile at a time. Theoretically we could post-process the OSM data to
remove duplicate nodes between the data types. (and if we do that we might
as well download the area from the API and do a check to see if the data
already exists).


>
> Maybe it would be useful to do a test subbasin with whatever toolchain
> you're
> going to use and then post it so that mappers can check to see how the
> conversion meshes with our general wants.
>
>
There have been several tests already and data has already been imported.
I'm happy to have people try out a subbasin as I'm running the conversion
scripts (I imagine it will take a while) so we can restart the conversion if
a bug is found.
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