[Talk-ca] Dealing with huge features

[Emilie Laffray]

2009/11/10 Sam Vekemans <acrosscanadatrails at gmail.com>

> One thing i forgot to mention,
>
> I'll use my trusty example on Vancouver Island
>
>
> http://www.openstreetmap.org/?lat=48.599&lon=-124.63&zoom=10&layers=B000FTFT
>
> Because the script 'chops up' that wooded area shp file into 'bite-sized
> chunks 2000)  once all the 'chunks get uploaded'' it turns out correct.
>
> Ie. the 'inners'  get loaded 1st, (and it looks funny) but once the
> 'outers' are loaded.. then it seems to fix its self.
>
> One way to handle that is this method (i might have used it for he area).
>
> 1 - load that big file to JOSM
> 2 - select the big polygon (outer ring) and 'delete'
> 3 - the result will look funny (but all those 'inners that are green, are
> still tagged correctly)
> 4 - upload to OSM all those 'inners'  (select top half and upload those
> 1st, then other half) and upload those (copying each selection to a new
> layer).
> 5 - when thats done... take  abreak :)
> 6 - in JOSM, hide all the other layers (accept the main osm.data)
> 7 - select that big outter ring and copy it to a new layer
> 8 - check the nodes size. (if it's STILL to big) cut it in half)
> 9 - upload that
> 10 - then when it renders in OSM.. it should be correct.
>
> Another option is to use PostGISmess
> - (my guess) is that you load the shp file into OpenJUMP  and then use the
> 'split area' option, where it cuts the whole thing into 5x5 (is nice an
> round 0.1 degree squares).
> -then save each square as a new file name (using A-Y)..
> -then let shp-to-osm do its tricks on each area.
>
> (Adam talked about that for a way to deal with downtown Vancouver with the
> automatch roads)
> ... so it would be only 1 or 2 tiles out of that, that would need to me
> manually worked with.
>

Huge polygons are becoming quite a problem. In your case, you have to use to
load in JOSM unfortunately.
For Corine, we decided to load the polygons manually after removing
intersect data. The rationale behind it is that it is a relation and that
people will load only a part of a chosen area when they are loading an area
and that it will not slow down their JOSM.
Also, we decided to have ways no longer than 1000 (the hard limit in API is
2000). The reason for that is that it allows people to add points easily to
ways that have been entered.
Breaking the polygon from a GIS software makes sense. Unfortunately, we
cannot use Osmosis to break down the polygon due to the way it works.
And I take exception to the fact that Postgis is a mess :)  It is a very
powerful tool to automate countless polygons without doing much :)

Emilie Laffray
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