[mkgmap-dev] Tiles pruned in DEM map

Wed Jan 13 09:41:58 GMT 2021

Hi Gerd

I don't think this is the point of the patch.

--order-by is known to increase the size of the main map. This is
accepted by users who consider the benefit worthwhile. The overview
map, needing to operate in the same environment, has to keep to the
same principals and this can lead to a size increase and the effect you
mention of a label being off-center, because the named area has been
split and the display software labels one part and suppress the label
on the other.

A good example depends on finding overlayed polygons that either:

a/ conflict with a given TYP [_drawOrder] - for example, using
mapnik.txt, you won't see any land features within Amenity/0x23,
Parking/0x05, Industrial/0x0c

b/ have equal [_drawOrder], ie most landuse areas etc, where what will
be displayed depends mostly on the internal logic of mkgmap, and,
slightly by OSM extract ordering and the original object complexity.

Finding these examples would be tedious. I originally noticed these
types of problems because the eTrex HCx starts displaying as soon as
possible, and I'd see interesting features disappear from the display
as it worked through everything that should be on the screen.

Ticker

On Wed, 2021-01-13 at 08:21 +0000, Gerd Petermann wrote:
> Hi Ticker,
> 
> I've hoped for a good example that shows how --order-by... really
> improves the overview map. I gave an example where the only visible
> difference is a label that is slightly off (so the patch worsens the
> map).
> 
> 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, 11. Januar 2021 12:39
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] Tiles pruned in DEM map
> 
> Hi Gerd
> 
> Here is an updated patch with the naming changes.
> 
> Ticker
> 
> On Wed, 2021-01-06 at 09:35 +0000, Gerd Petermann wrote:
> > Hi Ticker,
> > 
> > OK regarding the naming.
> > I think what I tried to point out is that the overview map probably
> > never suffers the problem that should be solved with the order-by
> > stuff, but on the other hand we really want to keep that map as
> > small
> > as possible to allow continent or maybe even planet wide overview
> > maps.  So, I really prefer to enable the shape merging for the
> > overview map.
> > A possible work around might be to merge the shapes before
> > MapSplitter is executed. The number of points is rather small, so
> > performance shouldn't be a problem as it is with real OSM data. We
> > might even use java.awt.area for that.
> > Another question is if the --order-by could/should be disabled for
> > the ovm_ maps.
> > 
> > Gerd
> > 
> > ________________________________________
> > Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> > von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> > Gesendet: Mittwoch, 6. Januar 2021 10:19
> > An: Development list for mkgmap
> > Betreff: Re: [mkgmap-dev] Tiles pruned in DEM map
> > 
> > Hi Gerd
> > 
> > Sorry about overview-dem-dists.
> > 
> > I'd prefer the Map variable to be called IsOverviewComponent to
> > make
> > clear the distinction between the 2 types of overview and to be
> > consistent with the names used in MapBuilder. I can do a patch to
> > this
> > effect.
> > 
> > --order-by is expected to increase the map size a bit; extra
> > polygon
> > splitting (in the ovm_ and carried into the composite) is performed
> > so
> > that all polygons at any given point are in the same subdivision
> > and
> > some merges (in both the ovm_ and the composite) are inhibited.
> > 
> > An overview map is unlikely to have multiple overlayed polygons so
> > probably there won't be any cases where a fixed _drawOrder couldn't
> > be
> > defined correctly, but it exists with the detail tiles that need a
> > TYP
> > where all _drawOrders are equal.
> > 
> > Ticker
> > 
> > On Tue, 2021-01-05 at 15:35 +0000, Gerd Petermann wrote:
> > > Hi Ticker,
> > > 
> > > there is a typo in the patch, overview-dem-dists instead of
> > > overview
> > > -dem-dist. My rather small overview map got 20MB instead of 181K
> > > ;)
> > > I also didn't like the idea that the overview map is recognized
> > > by
> > > the name. That can lead to strange effects with test maps, so I
> > > added
> > > a parameter.
> > > 
> > > With the corrections the size increases by only by 5K, but I have
> > > no
> > > idea how these 5K improve the map.
> > > I see one small difference where a label of a lake (1)  is placed
> > > a
> > > bit of the center. The "patched" map contains two polygons for
> > > this
> > > lake, I assume the Garmin software avoids to render its name
> > > twice
> > > but uses a different algo to calculate the position. These are
> > > the
> > > results for my own style, a variant of Minkos OpenFietsMap Light
> > > style.
> > > Will try again with default style and type file sameOrder.txt.
> > > 
> > > Gerd
> > > (1)
> > > https://www.openstreetmap.org/relation/3582977#map=14/53.5815/11.
> > > 19
> > > 91
> > > 
> > > ________________________________________
> > > Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im
> > > Auftrag
> > > von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> > > Gesendet: Dienstag, 5. Januar 2021 10:58
> > > An: Development list for mkgmap
> > > Betreff: Re: [mkgmap-dev] Tiles pruned in DEM map
> > > 
> > > Hi Gerd
> > > 
> > > shapeMergeFilter.merge() sorts the shapes according to typ,
> > > skipSize,
> > > fullArea and name. For --order-by to work for the overview, this
> > > must
> > > not happen; the order in the ovm_ files must be used. This is the
> > > same
> > > idea as when the more than 1 detail tiles are displayed on a
> > > device.
> > > 
> > > The size of osmmap.img for my test area, with the patch, is:
> > >  9216 --no-order-by-decreasing-area throughout
> > > 10752 --order-by-decreasing-area throughout
> > >  9219 --order-by-decreasing-area at start,
> > >       --no-order-by-decreasing-area for the combiners
> > > So, there is a slight increase, as expected, it really isn't of
> > > any
> > > significance.
> > > 
> > > --order-by-decreasing-area needs to be applied to both phases for
> > > it
> > > to
> > > work correctly.
> > > 
> > > If applied to the tile phase only, the overview map will render
> > > polygons in order of the results of the the shapeMergeFilter.
> > > 
> > > If applied to the overview phase only, probably similar; the
> > > order
> > > of
> > > the shapeMergeFilter governed ordering in the ovm_ .img
> > > 
> > > Ticker
> > > 
> > > On Mon, 2021-01-04 at 18:52 +0000, Gerd Petermann wrote:
> > > > Hi Ticker,
> > > > 
> > > > thanks for the patch. I'll have a closer look during the next
> > > > days.
> > > > I
> > > > don't yet understand why shapes aren't always merged.
> > > > What is the impact on the size of the overview map? What
> > > > happens
> > > > for
> > > > those users who create the overview map in an extra step that
> > > > doesn't
> > > > have the --order-by-decreasing-area option? What happens when
> > > > it's
> > > > the other way around, no --order-by-decreasing-area option for
> > > > the
> > > > tiles but --order-by-decreasing-area for the overview map?
> > > > 
> > > > Gerd
> > > 
> > > _______________________________________________
> > > mkgmap-dev mailing list
> > > mkgmap-dev at lists.mkgmap.org.uk
> > > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
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