[Talk-us] city polygons too large for potlatch to handle?

[Alan Brown]

Rather than "blowing it away", perhaps there should be a tool to automatically cut and replace large polygons with multiple smaller polygons?  Perhaps someone could write a routine using GPC:  http://www.cs.man.ac.uk/~toby/alan/software/ .  Years ago, when I worked at Etak, the internal format (mapengine) had a limit of 255 points per polygon; all software interfacing with it had to maintain this limit.  The limit doesn't have to be that low, but perhaps it should be low enough for Potlatch to handle anything.

Of course, the downside is that you can't assume that a polygon's border will the border of the administrative unit or physical feature represented.  (How is this handled for Oceans?)  The boundary polylines and polygons have to be distinct.

-Alan




________________________________
From: Chris Lawrence <lordsutch at gmail.com>
To: OpenStreetMap U.S. <talk-us at openstreetmap.org>
Sent: Tuesday, April 28, 2009 12:17:58 AM
Subject: Re: [Talk-us] city polygons too large for potlatch to handle?

On Tue, Apr 28, 2009 at 2:02 AM, Alan Brown <adbrown1967 at yahoo.com> wrote:
> This might not be the right group to direct this technical question - but
> I'll put it out there anyhow.
>
> I noticed a little while ago that city polygons where added to the OSM
> database (at least in the SF Bay Area) - and that's a good thing.  There is
> a city boundary that runs along a major road between San Jose and Campbell
> that I meant to clean up, by getting it to run along the median of the
> street.  I was also going to redigitize this road as the dual carriageway
> that it is.  Here's a junction between Bascom Ave, California Highway 85,
> and some of the city polygon boundaries:
>
>  http://www.openstreetmap.com/?lat=37.254578&lon=-121.951574&zoom=18&layers=B000FTF
>
> Every time I try to edit (or even select) the city polygon - to delete
> unnecesary points, or to get it to run nicely up the middle of the road -
> potlatch gets stuck in a loop.  It eventually shows me a warning:  "A script
> in this movie is causing Adobe Flash Player 10 to run slowly.  If it
> continues to run, your computer may become unresponsive.  Do you wish to
> abort the script?"  After which, it's impossible to complete the edit.
>
> This problem is making it difficult to clean up this street.  Are the
> developers aware of this problem?  Is there anything that can be done?  I
> was hoping that the new version of Potlatch would correct the problem, but
> it's not the case.

Ick.  It's possible the OSM API 0.6 upgrade brought in polygons & ways
that are now too big to edit because they're over the 0.6 limit of
2000 nodes per way--it is not at all clear what the migration for
existing polygons/ways was.  You may need to use JOSM to do at least a
basic edit on these polygons then upload and continue work in
Potlatch.

(Alternative theory: Potlatch has also just been generally flaky for
me post-upgrade, so it could just be Potlatch-flakiness.)

Worst comes to worst I can try to blow away the California upload and
upload a 0.6-friendly version.  I have a very nice, mostly-way-based
conversion setup respecting the 0.6 API limits and using complex
multipolygon relations that I implemented starting with the Idaho
(complete) and Illinois (uploading now) boundaries; ideally I'd like
to go back and redo the boundaries in the A-H states if I can think of
a sensible way to do it.  (Texas I will have to blow away and redo
anyway, which I'm not looking forward to.)


Chris

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