[mkgmap-dev] Option to output polygons in size order

Sun Jul 24 00:06:10 BST 2016

Hi Gerd

I'll need to some digging and understanding to get you IDs.
I don't think multi-polygons are the cause of my problems, rather the
standard British Isles map has an polygon place=island that covers the
whole of the mainland. Within it are many other areas, including nested
woods containing lakes, containing islands, containing ...
None of these show because "British Isles" is rendered on top of
everything. For some of the smaller islands around the coast of
Britain, features show correctly.

If I hack the style to suppress island when nam="British Isles" then
things show better.

If I was to have a Typ section with different _drawOrder levels,
imagine something like:
  Sea    1
  Island 2
  Woods/Forest...  3
  Lake   4
if the lake contains an Island with woods, they won't show because the
lake has higher level and is drawn on top.

I'd understood and hoped that, for areas with the same level it
rendered areas in file order, and I see on my device it overwriting,
sometimes woods with island, sometimes the other way around, depending
on, I presumed, the input ordering. I see the exactly the same
overwriting effect zooming in or scrolling in any direction.

What is the scale of the 'sub areas' you mention?

Ticker

On Sat, 2016-07-23 at 20:31 +0000, Gerd Petermann wrote:
> Hi Ticker,
> 
> okay, can you give an example where areas are causing problems?
> For example the id of a mp-relation?
> I ask because I assume that the problem is in the data.
> 
> Besides that the img format isn't that simple, it has different sub
> areas
> for one resolution, each can contain many polygons which don't have
> to
> fit into the sub area, in fact it is quite likely that a polygon in
> one sub area
> overlaps polygons in other sub areas. I assume that the order in
> which these
> sub areas are rendered depends on the direction you are moving.
> 
> Gerd
> 
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> Gesendet: Samstag, 23. Juli 2016 22:00:12
> An: mkgmap-dev at lists.mkgmap.org.uk
> Betreff: Re: [mkgmap-dev] Option to output polygons in size order
>  
> Hi Gerd
> 
> I don't understand how multi-polygon processing works, but was
> presuming that, if my idea works, sorting on the size of each
> individual polygon is the correct thing to do.
> 
> Partial overlap of polygons is generally not a problem I'm trying to
> solve here, and it is unlikely that, say, if there is a field next to
> a
> wood with a lake spanning the two, the mapping data would have 2 land
> areas fully abutted with the lake overlapping both; I'd expect there
> to
> be 3 distinct, non-overlapping, areas.
> 
> Ticker
> 
> On Sat, 2016-07-23 at 19:23 +0000, Gerd Petermann wrote:
> > Hi Ticker,
> > 
> > mkgmap analyses multipolygon relations and cuts inner parts, so
> > correct mp-relations
> > should not be a problem. I've seen overlapping polygons, e.g. when
> > you chose to render
> > place=island and also the land polygons created by the sea
> generator.
> > You suggest to write the larger polygon first, but in those cases
> > this would not help.
> > I think this solution would also not help when polygons partially
> > overlap.
> > 
> > Gerd
> > Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> > von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> > Gesendet: Samstag, 23. Juli 2016 20:42:02
> > An: mkgmap-dev at lists.mkgmap.org.uk
> > Betreff: Re: [mkgmap-dev] Option to output polygons in size order
> >  
> > Hi
> > 
> > I'm sure that the order in the map has some effect on the Legend;
> as
> > I
> > zoom in or scroll across areas with greenery they appear briefly
> and
> > are then cleared, by the island polygon that covers everything, as
> it
> > starts drawing the ways...
> > 
> > Generally, the openStreetMap data order is OK, but I have found
> > examples where there are lakes, within the same meadow, that occur
> > both
> > before and after it. Not sure if this is related to multi-polygons,
> > but
> > if sorting was performed on the individual polygons there wouldn't
> be
> > any problem.
> >  
> > Also it looks like splitter is delaying the British Isles (and
> other
> > large) polygons because they occurs on multiple tiles.
> > 
> > Typ _drawOrder cannot solve the problem when there are nested
> > polygons
> > with more that one instance of the same type, whereas drawing outer
> > ones first solves it completely.
> > 
> > I have seen mention somewhere that areas with the same _draworder
> are
> > rendered in file order
> > 
> > Ticker
> > 
> > On Sat, 2016-07-23 at 17:17 +0000, Gary Bamford wrote:
> > > Hi Ticker/Gerd
> > > 
> > > The draw order does work for the Legend ( it is the device I have
> > ).
> > > I also came across problems with multiple polygons, the problem
> can
> > > be one of several things, not all multi polygons are correct on
> > > openstreetmap, I cam across one today "fairhaven lake"  golf
> > course,
> > > was hiding, due to draw order, but the problem was, it is
> contained
> > > within a polygon for a residential area, so I had to change the
> > data
> > > on openstreetmap, to make it an inner polygon. when i download
> the
> > > new OSM data I expect it to work correctly.
> > > 
> > > if the polygons are set correctly on openstreetmap, then draw
> order
> > > will will as you expect. 
> > > 
> > > Gary
> > > 
> > > From: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> on
> behalf
> > > of Gerd Petermann <GPetermann_muenchen at hotmail.com>
> > > Sent: 23 July 2016 17:05
> > > To: Development list for mkgmap
> > > Subject: Re: [mkgmap-dev] Option to output polygons in size order
> > >  
> > > Hi Ticker,
> > > 
> > > are you sure that the order matters? I've never heard that theory
> > > and I would be surprised when that is true.
> > > The normal way to handle the draw order is to use a typ file, not
> > > sure
> > > if this works on your device, but it seems to work well for
> others.
> > > 
> > > Gerd
> > > Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im
> Auftrag
> > > von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> > > Gesendet: Samstag, 23. Juli 2016 18:45:59
> > > An: mkgmap development
> > > Betreff: [mkgmap-dev] Option to output polygons in size order
> > >  
> > > Hi
> > > 
> > > I'm using splitter-r437/mkgmap-r3676 to make a map for Etrex
> Legend
> > > from british-isles-latest.osm.pbf from geofabric.de.
> > > 
> > > Using "default" style and not using a TYP file, no land features
> > > (woods,marsh,green) show because an island polygon for "British
> > > Isles"
> > > is rendered near the end, on top of everything else. I guess that
> > the
> > > Etrex has all area types as the same draworder and renders them
> in
> > > file
> > > order.
> > > 
> > > I presume I could use TYP / _DrawOrder to change this behaviour
> > > slightly but I keep finding examples of woods in islands in lakes
> > in
> > > marsh in islands etc etc, so _DrawOrder can't solve the problem.
> > > 
> > > What would make everything show correctly would be to output
> > polygons
> > > in size order, largest to smallest. Could this be done easily?
> > either
> > > in splitter then --preserve-element-order, or in mkgmap, possibly
> > > after
> > > style processing because there will be a lot fewer polygons at
> this
> > > point.
> > > 
> > > Regards
> > > Ticker Berkin
> > > 
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