[Talk-us] Systematic errors in the Maui, Hawaii Data

Dave Hansen dave at sr71.net
Tue Sep 29 19:42:30 BST 2009


On Tue, 2009-09-29 at 11:20 -0700, Scott Atwood wrote:

> I spot checked a number of locations all around Maui, and in all the
> locations I checked, they seem to be affected by the same or highly
> similar offset to the NNW.  Here is another example from the Lahaina
> area:
> 
> http://www.openstreetmap.org/?lat=20.88606&lon=-156.68522&zoom=15&layers=B000FTF

If you can look into formalizing this, I'd be willing to take a look at
it.  What I mean is to take some precise measurements from a wide set of
samples across the island, probably 20 or 30.  Figure out what the
displacement vector is at each point, and ensure that it *is*
consistent.  The worst thing we could do would be to perform such an
edit and later realize that we've hurt more than we've helped.

I'm just really hesitant to go moving an entire island worth of data
based on the problem I've seen so far.  

> The prospect of manually shifting every single street on the entire
> island of Maui (even in batches within JOSM) is extremely daunting,
> and strongly inhibits me from wanting to do any work on Maui.  And the
> fact that such enormous errors persist suggests to me that few if any
> people have done much non-automated work on Maui yet.

The question is whether it will take longer for people to do it manually
or if doing it in an automated way will be more efficient.  Believe me,
the prospect of doing a mass edit like that is pretty daunting as well.

> Can we verify how much editing has been done on Maui? If it is as
> little as I think, there is little to loose by throwing away the
> existing data and starting over. I still think re-importing (or some
> kind of automated batch editing) might be a faster and easier way to
> fix the problems with Maui.

Sure.  Just download the entire island and see how many objects have
been touched by people other than DaveHansen.  JOSM can tell you this
pretty quickly.

-- Dave





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