[mkgmap-dev] Squaring off of land outlines

Wed Jan 29 11:09:39 GMT 2020

Hi

I have always used the default for this, including the skipSizeFilter
bit for sea as in the default style and had never noticed a problem.

I'm now about to experiment with --min-size-polygon=4.

The value of this option is in Garmin map units, regardless of the
resolution of the sub-map. Assuming it is worthwhile, wouldn't it be
better of the value was taken as 'current-resolution-units'?

I assume that, at low resolutions, polygons that degenerate into a
single point or line are chucked anyway, so a value of <= 8 is
irrelevant for resolution <= 18

Ticker

On Wed, 2020-01-29 at 10:50 +0000, Gerd Petermann wrote:
> Hi Mike,
> 
> thanks for the reminder. It  seems that I somehow missed v7 of the
> patch.
> Let's postpone the changes regarding the size filter. I first like to
> get more feedback.
> Will test v7 now...
> 
> Gerd
> 
> ________________________________________
> Von: Mike Baggaley <mike at tvage.co.uk>
> Gesendet: Mittwoch, 29. Januar 2020 11:43
> An: 'Gerd Petermann'; 'Felix Hartmann'; 'Development list for mkgmap'
> Betreff: RE: [mkgmap-dev] Squaring off of land outlines
> 
> Hi Gerd, setting the default to 0 sounds sensible. The documentation
> of
> --min-size-polygon doesn't mention you can set it to 0 to turn it off
> (it is
> mentioned in --polygon-size-limits, but this seems to me to be the
> wrong
> place). The recommendation of 8-15 gives no indication of what these
> values
> actually mean or whether 15 means remove more or less than 1.
> 
> Are you expecting anything further from me on the documentation patch
> I
> supplied earlier? I could include an update to this section: changing
> the
> default, moving the meaning of 0 from --polygon-size-limits to
> --min-size-polygon, including a mention of mkgmap:skipSizeFilter=true
> to
> override it for specific polygon types and giving more information on
> what
> the values mean (for the last one I would need some info).
> 
> Cheers,
> Mike
> 
> -----Original Message-----
> From: Gerd Petermann [mailto:gpetermann_muenchen at hotmail.com]
> Sent: 29 January 2020 09:51
> To: Mike Baggaley <mike at tvage.co.uk>; 'Felix Hartmann'
> <extremecarver at gmail.com>; 'Development list for mkgmap'
> <mkgmap-dev at lists.mkgmap.org.uk>
> Subject: Re: [mkgmap-dev] Squaring off of land outlines
> 
> Hi Mike,
> 
> the size filter "looks" at the polygons which are to be added to the
> map.
> Those polygons are the result of a long chain of split and merge
> processes
> followed by rounding which - sometimes - produce rather small shapes.
> The
> sea multipolygon is split into parts of no more than 255 points. So,
> the
> more detailed the mapping of the coastline the smaller those parts.
> This process is not optimal, see also the todo list (1).
> I've done a few tests with the default option (--min-size-polygon=8)
> and
> default style with the options given in examples/sample.cfg and I
> think most
> of the dropped elements at low resolutions should have been kept. For
> small
> map tiles like yours even the background (0x4b) polygon is dropped.
> The effect of the filter reg. img size is rather small thus it also
> has
> nearly no effect on throughput times.
> 
> My suggestion would be to change the default to 0 for the --min-size
> -polygon
> option. Suggested reasonable values should be in the range of 0-8 and
> maybe
> print a warning if --min-size-polygon is used with a value > 8.
> 
> Gerd
> (1) http://www.mkgmap.org.uk/dev/todo
> 
> ________________________________________
> Von: Mike Baggaley <mike at tvage.co.uk>
> Gesendet: Mittwoch, 29. Januar 2020 10:22
> An: 'Gerd Petermann'; 'Felix Hartmann'; 'Development list for mkgmap'
> Betreff: RE: [mkgmap-dev] Squaring off of land outlines
> 
> In the case where this is causing squaring off of the sea polygon,
> the
> coastline is not usually small even at the low resolution. So why is
> the
> size filter discarding it?  Is it because the object is crossing a
> tile
> boundary and the part within a tile is small? If that is the case, it
> would
> make sense to not discard any object that is touching the tile
> boundary.
> 
> Regards,
> Mike
> 
> -----Original Message-----
> From: Gerd Petermann [mailto:gpetermann_muenchen at hotmail.com]
> Sent: 29 January 2020 01:20
> To: Felix Hartmann <extremecarver at gmail.com>; Development list for
> mkgmap
> <mkgmap-dev at lists.mkgmap.org.uk>
> Subject: Re: [mkgmap-dev] Squaring off of land outlines
> 
> Hi all,
> 
> the default style adds buildings only with resolution 24. The size
> filter is
> disabled at this resolution. The area_size() style function allows to
> filter
> small polygons at this resolution.
> The size filter compares the width or height of the bounding box of
> the
> object AFTER all points where rounded to the given resolution.
> The rounding can produce a bbox which is smaller than the original
> object
> and thus produce the gaps in sea. I am pretty sure that you will also
> see
> those gaps with huge natural=wood or natural=water multipolygons if
> they are
> mapped in great detail when the size filter is used with default
> value
> (--min-size-polygon=8)
> I think this default is too high and the documentation even suggests
> to use
> a higher value.
> 
> Gerd
> 
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> von
> Felix Hartmann <extremecarver at gmail.com>
> Gesendet: Dienstag, 28. Januar 2020 23:52
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] Squaring off of land outlines
> 
> Performance of map on device is drastically improved you you kick out
> those
> tiny polygons. Especially in cities where people have detail mapped
> all
> buildings. If you don't have building=yes or building=* in your style
> - then
> you can likely live with the filter disabled (not sure how much
> bigger the
> map data gets).
> 
> On Tue, 28 Jan 2020 at 21:41, Gerd Petermann
> <gpetermann_muenchen at hotmail.com<mailto:
> gpetermann_muenchen at hotmail.com>>
> wrote:
> Hi Mike,
> 
> "sea" is build from shapes (= polygons).
> The size filter is not explained in the style manual, but in the
> options
> --min-size-polygon and --polygon-size-limits.
> Unfortunately the filter works a bit unpredictable at low
> resolutions, so in
> my eyes it is a good idea to disable.
> I've never fully understood the purpose of this filter. I think it
> should
> improve performance, but it seems to decrease quality even more.
> 
> You may play with --min-size-polygon=0 to see what happens when the
> filter
> is disabled.
> 
> Gerd
> 
> ________________________________________
> Von: Mike Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>
> Gesendet: Dienstag, 28. Januar 2020 21:21
> An: 'Gerd Petermann'; 'Development list for mkgmap'
> Betreff: RE: [mkgmap-dev] Squaring off of land outlines
> 
> Brilliant! A big improvement! It still doesn't exactly match the land
> polygon, but that doesn't matter for my purposes. I suggest changing
> the to
> do list so it says use the same algorithm for shapes, lines and sea.
> I also
> suggest adding a sentence to the style manual in the explanation of
> mkgmap:skipSizeFilter - the description doesn't explain the purpose
> or what
> the effect is of passing the size filter.
> 
> Thanks for your assistance,
> Mike
> 
> -----Original Message-----
> From: Gerd Petermann
> [mailto:gpetermann_muenchen at hotmail.com<mailto:
> gpetermann_muenchen at hotmail.c
> om>]
> Sent: 28 January 2020 19:03
> To: Mike Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>
> Subject: AW: [mkgmap-dev] Squaring off of land outlines
> 
> Hi Mike,
> 
> some small rather small sea polygons are filter by the size filter.
> Change the statememnt for sea polygons to this:
> natural=sea {add mkgmap:skipSizeFilter=true; name '${name}'} [0x32
> resolution 14]
> 
> See also the corresponding rule in the default style:
> natural=sea {add mkgmap:skipSizeFilter=true; set mkgmap:drawLevel=2}
> [0x32
> resolution 10]
> 
> Gerd
> 
> ________________________________________
> Von: Mike Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>
> Gesendet: Dienstag, 28. Januar 2020 19:39
> An: 'Gerd Petermann'
> Betreff: RE: [mkgmap-dev] Squaring off of land outlines
> 
> Thanks Gerd. I has been considering trying to find the problem
> myself, but
> I'm not familiar with the writing sections of code, and they are
> complicated
> to get to grips with.
> 
> Cheers,
> Mike
> 
> -----Original Message-----
> From: Gerd Petermann
> [mailto:gpetermann_muenchen at hotmail.com<mailto:
> gpetermann_muenchen at hotmail.c
> om>]
> Sent: 28 January 2020 16:16
> To: Mike Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>;
> 'Development
> list for mkgmap'
> <mkgmap-dev at lists.mkgmap.org.uk<mailto:mkgmap-dev at lists.mkgmap.org.uk
> >>
> Subject: AW: [mkgmap-dev] Squaring off of land outlines
> 
> Hi Mike,
> 
> okay, I'll have a closer look now.
> 
> Gerd
> 
> ________________________________________
> Von: Mike Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>
> Gesendet: Dienstag, 28. Januar 2020 16:51
> An: 'Gerd Petermann'; 'Development list for mkgmap'
> Betreff: RE: [mkgmap-dev] Squaring off of land outlines
> 
> Hi Gerd, the problem I have is not the one in the to do list. If I
> add the
> polygon fill for natural=coastline, this does produce a different
> outline
> than the one for the line, but both are reasonable approximations and
> neither contains unexpected artefacts. The sea generation
> approximation is
> wildly different and contains unwanted artefacts.  Please see the
> attached
> image that contains land in brown, sea in blue and an area of white
> that is
> not filled by either. I believe this is a bug in the sea generation
> code. I
> would expect sea generation to use the same algorithm as for filled
> areas so
> that holes are not left. I'm not too worried about the line being
> slightly
> different.
> 
> Regards,
> Mike
> 
> -----Original Message-----
> From: Gerd Petermann
> [mailto:gpetermann_muenchen at hotmail.com<mailto:
> gpetermann_muenchen at hotmail.c
> om>]
> Sent: 28 January 2020 14:59
> To: Mike Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>;
> 'Development
> list for mkgmap'
> <mkgmap-dev at lists.mkgmap.org.uk<mailto:mkgmap-dev at lists.mkgmap.org.uk
> >>
> Subject: AW: [mkgmap-dev] Squaring off of land outlines
> 
> Hi Mike,
> 
> See last point in the todo list: http://www.mkgmap.org.uk/dev/todo
> I think what you see is exactly the result of the two different
> algos.
> I can only suggest to omit the rendering of polygon outlines at
> resolutions
> below 24.
> 
> ________________________________________
> Von: Mike Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>
> Gesendet: Dienstag, 28. Januar 2020 15:23
> An: 'Gerd Petermann'; 'Development list for mkgmap'
> Betreff: RE: [mkgmap-dev] Squaring off of land outlines
> 
> Hi Gerd, I have produced a small sample which demonstrates the
> problem. It
> contains one very small island. I have cut down the style to a bare
> minimum
> with just two resolutions: 24 and 14 containing just sea and a
> coastline
> outline. At resolution 24 the sea and coastline are coincident. At
> 14, they
> are wildly different. The coastline at low resolution includes a spur
> which
> is a complication. The ideal sea boundary would be the same as the
> coastline, but with the spur removed (or perhaps the spur should not
> be on
> the coastline either). I have included the style, typ file, command
> line in
> a batch file and osm data in the attached zip. Please let me know if
> you
> need anything else.
> 
> Cheers,
> Mike
> 
> -----Original Message-----
> From: Gerd Petermann
> [mailto:gpetermann_muenchen at hotmail.com<mailto:
> gpetermann_muenchen at hotmail.c
> om>]
> Sent: 28 January 2020 08:26
> To: Mike Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>;
> 'Development
> list for mkgmap'
> <mkgmap-dev at lists.mkgmap.org.uk<mailto:mkgmap-dev at lists.mkgmap.org.uk
> >>
> Subject: AW: [mkgmap-dev] Squaring off of land outlines
> 
> Hi Mike,
> 
> I can try to find out what's wrong but I would need a lot more
> details about
> your map creation process. Could be an error in mkgmap or in the OSM
> data or
> in the --levels option or in the --min-size-polygon option or
> --polygon-size-limits or ...
> 
> Gerd
> 
> ________________________________________
> Von: mkgmap-dev
> <mkgmap-dev-bounces at lists.mkgmap.org.uk<mailto:
> mkgmap-dev-bounces at lists.mkgm
> ap.org.uk>> im Auftrag von Mike
> Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>
> Gesendet: Montag, 27. Januar 2020 19:07
> An: 'Development list for mkgmap'
> Betreff: Re: [mkgmap-dev] Squaring off of land outlines
> 
> HI Gerd, I don't have an old map, but this has been happening for
> some time
> - I am not sure whether it has always done this, but thought it would
> be
> worth trying a few old versions to see whether it is bug that got
> introduced, or is one that has always been there. It looks similar to
> the
> problem reported on Feb 18 2017 with "Terraced/pixellated coastline
> with
> --precomp-sea" as the title. I am not using --precomp-sea, but the
> problem I
> am getting is also in the sea outline. NopMap indicated that his
> problem was
> fixed in r3819, however, I have downloaded the source to that version
> and
> compiled it, and it exhibits the same problem for me.
> 
> Regards,
> Mike
> 
> -----Original Message-----
> From: Gerd Petermann
> [mailto:gpetermann_muenchen at hotmail.com<mailto:
> gpetermann_muenchen at hotmail.c
> om>]
> Sent: 27 January 2020 08:36
> To: 'Development list for mkgmap'
> <mkgmap-dev at lists.mkgmap.org.uk<mailto:mkgmap-dev at lists.mkgmap.org.uk
> >>
> Subject: Re: [mkgmap-dev] Squaring off of land outlines
> 
> Hi Mike,
> 
> I am not aware of a folder that keeps all older releases or an error
> that
> would be related to this.
> Are you sure that you didn't change mgkmap options like --levels or
> the
> style or the typ file?
> Do you still have a map which looks better? In that case you should
> find the
> string mkgmap in the img file, e.g. "mkgmap-r4431"
> 
> Gerd
> 
> 
> ________________________________________
> Von: mkgmap-dev
> <mkgmap-dev-bounces at lists.mkgmap.org.uk<mailto:
> mkgmap-dev-bounces at lists.mkgm
> ap.org.uk>> im Auftrag von Mike
> Baggaley <mike at tvage.co.uk<mailto:mike at tvage.co.uk>>
> Gesendet: Montag, 27. Januar 2020 01:43
> An: 'Development list for mkgmap'
> Betreff: [mkgmap-dev] Squaring off of land outlines
> 
> Hello,
> 
> I am getting squaring off of the outline between land and sea at low
> zoom
> levels (less than 16) - see attached BaseCamp images of Gran Canaria
> at
> resolution 16 and at resolution 14 displayed at the same size.
> Obviously
> some reduction in accuracy is expected at lower zoom level, but not
> these
> artefacts. I'm not sure when this started happening but believe it
> was some
> time ago. I can't seem to find the old releases to try previous
> versions,
> http://svn.mkgmap.org.uk/mkgmap/releases/ just shows me an empty
> folder. Can
> you point me to the correct download folder that contains the
> previous jar
> files, and/or let me know if this is a known problem, and if so
> whether
> there is a workaround?
> 
> Thanks,
> Mike
> 
> 
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk<mailto:mkgmap-dev at lists.mkgmap.org.uk>
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
> 
> 
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk<mailto:mkgmap-dev at lists.mkgmap.org.uk>
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
> 
> 
> --
> Felix Hartman - Openmtbmap.org & VeloMap.org
> Schusterbergweg 32/8
> 6020 Innsbruck
> Austria - Österreich
> 
> 
> 
> 
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev