[mkgmap-dev] low-res-opt branch: error message from ShapeSplitter for self-intersecting multipolygon

Mon Jun 14 17:30:21 BST 2021

Hi Ticker,

reg. my test which compares area sizes: It is normal that the size of the area changes a bit when the cut adds points in the middle of long segments. You can see the difference in JOSM when you zoom in.

Besides that I think that ShapeSplitter should not drop anything that is visible.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
Gesendet: Montag, 14. Juni 2021 18:14
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] low-res-opt branch: error message from ShapeSplitter for self-intersecting multipolygon

But going back to running GBR, I'm getting more errors - I'll have to
see if there is a compromise.

Ticker

On Mon, 2021-06-14 at 16:39 +0100, Ticker Berkin wrote:
> Hi Gerd
>
> Made some progress! I needed to disable the EPS_HP=2 tolerance along
> the cut line otherwise there were correct cases that could be
> interpreted incorrectly. I also needed not to chuck away very small
> areas otherwise your test complained. The major problem was valid
> shapes that had parts with zero area when cut and passed through the
> same point on the cut-line as another line.
>
> The main tiles in xxx.zip now build without error with order-by and
> no
> -order-by, even with ShapeMergeFilter maxPoints = 65535.
>
> However, the overview builder, when --no-order-by and --improve
> -overview, fails splitting. The shape presented to ShapeSplitter has
> obvious self-intersections (with --order-by, shape merge is disabled
> in
> the overview builder)
>
> Ticker
>
> On Mon, 2021-06-14 at 08:28 +0000, Gerd Petermann wrote:
> > Hi Ticker,
> >
> > I am still testing with the files in
> > https://files.mkgmap.org.uk/download/507/xxx.zip
> >
> > I applied the attached patch to enable massive merging and
> > simulating
> > possible splits and your splitShapeFix_10_lowRes.patch and I see
> > several error messages.
> > The previously attached example comes from xxx\63240004.osm.pbf
> >
> > My options:
> > --output-dir=e:\ld  --gmapi --generate
> > -sea=multipolygon,floodblocker
> > --preserve-element-order --order-by-decreasing-area
> > --allow-reverse-merge   --improve-overview --min-size-polygon=2
> > -c e:\xxx\template.args
> >
> > Gerd
> >
> > ________________________________________
> > Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> > von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> > Gesendet: Montag, 14. Juni 2021 10:19
> > An: Development list for mkgmap
> > Betreff: Re: [mkgmap-dev] low-res-opt branch: error message from
> > ShapeSplitter for self-intersecting multipolygon
> >
> > Hi Gerd
> >
> > Any form of self-intersection might cause problems to
> > ShapeSplitter.
> > Not sure what you mean by "connected hole visited.." - I presume
> > something like the outer edge of the shape is clockwise, with a cut
> > leading to a hole that is also clockwise; for this to happen the
> > in/out
> > lines from the edge to the hole conceptually cross.
> >
> > I'm just running low-res-opt on BritishIsles with ShapeMergeFilter
> > maxPoints=65535 to see if I can get a problem to work on. What is
> > your
> > test area?
> >
> > Also, the latest development versions of the suspect code areas are
> > in
> > different branches. Should I attempt to have a composite with the
> > faster-mp bits of MP handling and low-res-opt version of
> > ShapeMergeFilter?
> >
> > Your attached example looks OK and I wouldn't have expected it to
> > cause
> > any difficulties for the later versions of ShapeSplitter. A
> > possible
> > difficulty might be an almost horizontal line close to the in/out
> > lines
> > to the lower shape. I hope my attempt to allow a bit of tolerance
> > where
> > calculated points on the cut-line end up 1/2 HP units the wrong way
> > round isn't causing other problems. Do you have this as an example
> > I
> > can test?
> >
> > Ticker
> >
> >
> > On Sun, 2021-06-13 at 14:17 +0000, Gerd Petermann wrote:
> > > Hi Ticker,
> > >
> > > OK, my current understanding is that ShapeSplitter may fail to
> > > split
> > > 8-like shapes or shapes where the connected hole is visited in
> > > the
> > > "wrong" direction. Those problem cases are possibly created by
> > > 1) MultipolygonRelation.joinways()
> > > 2) MultipolygonCutter
> > > 3) ShapeMergeFilter (maybe)
> > >
> > > Do you see a way to avoid them in those routines? Attached is
> > > another
> > > example that doesn't work.
> > >
> > > Gerd
> >
> > _______________________________________________
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> > mkgmap-dev at lists.mkgmap.org.uk
> > https://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
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