[mkgmap-dev] mkgmap-dev Digest, Vol 153, Issue 40 Resolution 23 raster problems

Thu Apr 29 13:30:57 BST 2021

Yes - I also support Gerd that it doesn't work well for polygons.
Now for lines it's another story.
a) I love that lines are a bit straighter and looking better vs increasing
douglas peucker.
b) Sadly though there are bits and pieces of roads missing. If that is
fixed I would be all supportive to use this for all lines. But not before
those missing bits reappear.
How to check for it - just use lowest detail level in Basecamp.

Oh yeah and mkgmap without that patch also has a zig zagging problem. Maybe
we would need a separate algorithm to check for zig zagging and make sure
this does not happen. I really think we could need an algorithm that just
checks for zig zagging from resolution 22 and lower and base it on the
principle that 90% of all those zig zags are unwanted therefore just
straighten lines if there is a zig zag.
So nothing to do with this patch - but a general really needed improvement
for mkgmap. (mkgmap is lacking a bit vs Garmin owns map at lower
resolutions. At resolution 24 mkgmap produces fantastic maps, but garmins
own maps are definitely better at lower resolutions regarding problems like
zig zagging or reducing detail). Avoiding those zig zags would make the
maps pan and load much faster on devices. I use a high DP value of 5.4
because zoomed out further I feel this is needed. But the zig zagging
occurs anyhow, or because of it?

I really feel some little tweaks here could be a huge improvement for
practical use on devices. We do not need exactness when zoomed out far -
but we need the map to look nice. If a line is 1 or 2 points away from
reality doesn't matter from resolution 17-21 and matters not too much for
resolution 22. Only 23 and 24 should be more or less exact. (maybe for
driving on highways with a car this is different - but is anyone actually
using mkgmap created maps for this? I think nearly everyone uses google
maps or smartphone. Garmin maps are mainly for outdoors or city maybe. But
not for automobile use. Some people but not many motorcycle maybe. So the
main importance for lower resolution is nice visual display and fast, not
if a road misses some tiny turn or is 100m left or right. And with a car we
have lock on road exactly for that. So visually it will be on the road
anyhow even if the road is moved 1 or 2 garmin units to one side.

On Wed, 28 Apr 2021 at 22:59, Gerd Petermann <
gpetermann_muenchen at hotmail.com> wrote:

> Hi all,
>
> my observations at resolution 22:
> I think the patch re-introduces rendering problems at T-shaped crossings,
> sometimes they look like t-shapes at lower resolutions.
> Sample: https://www.openstreetmap.org/node/260418111
>
> It seems to filter more small polygons, even with  --min-size-polygon=0.
> I think it tends to make polygons smaller, not sure why.
>
> It sometimes reduces wrong zig-zagging, but only for ways with many
> points. In cities, where roads are often split into many small parts it
> sometimes makes things worse.
>
> It probably helps for the special case contour lines and therefore I
> suggest to limit it to them.
>
> Maybe the code to find the best place for a rounded coord should also
> consider to remove the point if that would give the best result.
>
> Gerd
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von
> Gerd Petermann <gpetermann_muenchen at hotmail.com>
> Gesendet: Mittwoch, 28. April 2021 15:21
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] mkgmap-dev Digest, Vol 153, Issue 40 Resolution
> 23 raster problems
>
> Hi Felix,
>
> I expect (more) small missing parts of complex shapes like forests or
> waterway areas (those without mkgmap:skipSizeFilter=true) and more obvious
> differences between shapes and lines, e.g. if a style renders outlines of
> buildings.
>
> The maps are very different at res 22, so it is hard to say if there are
> more  improvements then worsenings.
>
> I've experimented with different orders of filters in the past. It's
> difficult to test because the changes heavily depend on the Styte AND the
> mapped objects AND the mappers preferences. For example, if landuse areas
> are glued to highways or not, if landuse areas are glued to other landuse
> areas or if there nodes are just very close.
>
> Gerd
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von
> Felix Hartmann <extremecarver at gmail.com>
> Gesendet: Mittwoch, 28. April 2021 14:58
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] mkgmap-dev Digest, Vol 153, Issue 40 Resolution
> 23 raster problems
>
> Oh I thought it was mainly meant for contourlines. Did not know you intend
> it to be used in general. I am not really sure how and where to check for
> quality.
>
> On Wed, 28 Apr 2021 at 20:13, Gerd Petermann <
> gpetermann_muenchen at hotmail.com<mailto:gpetermann_muenchen at hotmail.com>>
> wrote:
> Hi Felix,
>
> your screen shots only show contour lines but the patch works on all types
> of lines and polygons. So, please also check the results with other maps.
>
> Gerd
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk<mailto:
> mkgmap-dev-bounces at lists.mkgmap.org.uk>> im Auftrag von Felix Hartmann <
> extremecarver at gmail.com<mailto:extremecarver at gmail.com>>
> Gesendet: Mittwoch, 28. April 2021 04:54
> An: Development list for mkgmap; Andrzej Popowski
> Betreff: Re: [mkgmap-dev] mkgmap-dev Digest, Vol 153, Issue 40 Resolution
> 23 raster problems
>
> forgot 1.3 value - that is good enough (and this location is not the most
> difficult, but there are very few places that are worse. So I feel it's
> good enough as if it's fine here - there are very very few other places
> that are still problematic.
>
>
> On Wed, 28 Apr 2021 at 10:50, Felix Hartmann <extremecarver at gmail.com
> <mailto:extremecarver at gmail.com><mailto:extremecarver at gmail.com<mailto:
> extremecarver at gmail.com>>> wrote:
> Thanks for that patch, the improvement is not as big as from the previous
> patch - but there is some.
> I analysed it a bit more - and I think there needs to be one more change -
> actually in general and not only for contourlines.
>
> We need different values for the douglas peucker algorithm depending on
> resolution!
>
> Right now we can only set one value, and that is multiplied for each
> resolution?
> Based on the current state I would like to have
>
> resolution
> 24= 0.0 or maybe actually have it active at 24 as well trying a value of
> 0.3 or so. Where there any problems with autorouting or why is it not
> possible to use it at resolution 24 as well?
> 23=1.3
> 22=2.6
> 21=3.9
> 20-11=5.4
>
>
> Especially if we produce a map without resolution 24, then resolution 23
> needs to have much lower DP value than the subsequent resolutions. Using
> 1.3 for resolution 23 makes the quality IMHO good enough to be used for an
> contourlines only map for GPS devices and skipping resolution 24
> altogether. For Desktop use resolution 24 may still make sense for
> contourlines - but even then the difference is only in very steep areas.
>
> Attached some screenshots at resolution 24, and at 23 with different DP
> values and one of patch2.
>
> On Tue, 27 Apr 2021 at 23:16, Andrzej Popowski <popej at poczta.onet.pl
> <mailto:popej at poczta.onet.pl><mailto:popej at poczta.onet.pl<mailto:
> popej at poczta.onet.pl>>> wrote:
> Hi,
>
> some more experiments, see attached patch. I have tried to optimize
> rounding of coordinates for lowest distance to line. This is not good
> for polygons, because can creates gaps between adjacent polygons.
>
> --
> Best regards,
> Andrzej
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>
>
> --
> Felix Hartman - Openmtbmap.org & VeloMap.org
>
>
>
> --
> Felix Hartman - Openmtbmap.org & VeloMap.org
>
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>
>
> --
> Felix Hartman - Openmtbmap.org & VeloMap.org
>
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-- 
Felix Hartman - Openmtbmap.org & VeloMap.org
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