[Talk-us] hyrdography imports

SteveC steve at asklater.com
Wed Feb 10 15:59:15 GMT 2010


On Feb 10, 2010, at 8:48 AM, Mike N. wrote:

>> any way the importer can
>> 
>> a) go back and fix all the millions of duplicated nodes
>> 
>> b) not do it in future?
> 
>  I'm working on both points -
> 
> a) Happens in several cases:
>  1. At the joining of streams to waterbodies.  The duplicate happens 
> because data comes from 2 separate sources (Flowlines and Waterbodies / 
> Areas).   There needs to be a higher level view to combine them.  The number 
> of duplicates is relatively small.
>  2. NHD features are placed into multiple NHD 'sub-basin extracts'. 
> Those could be eliminated at OSM conversion time if the conversion scripts 
> were to have access to all features previously imported.   This can result 
> in many duplicates.
>   3.  Adjoining area types from NHD do not share nodes, but should.   I was 
> able to cobble together a manual Perl script to fix this up as features are 
> imported, but it's not a good general solution.

is this covered - it seems to happen at every single stream intersection?

> b.)  All current scripts I know of require significant rework, short of 
> importing the NHD into a local GEO database, then exporting it to remove 
> duplicate nodes.
> 
> 
> Should we halt all US Hydro import work until this is resolved?

personally I think so, I'm fixing stuff in CO just to get a feel for it

> 
> 
> 
> 
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Yours &c.

Steve





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