[mkgmap-dev] Request - set --reduce-point-density= for each resolution

Sat May 1 11:44:48 BST 2021

That could well be - it does seem a bit strange that pretty straight roads
become so zig zagged - surely also taking up more space in the map itself.

On Sat, 1 May 2021 at 17:23, Gerd Petermann <gpetermann_muenchen at hotmail.com>
wrote:

> Hi Felix,
>
> I think one reason for the zig-zagging is that we don't merge roads at
> lower resolutions and maybe DouglasPeucker should ignore "preseved" points
> at level 1 and higher.
>
> Gerd
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von
> Felix Hartmann <extremecarver at gmail.com>
> Gesendet: Samstag, 1. Mai 2021 11:17
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] Request - set --reduce-point-density= for each
>       resolution
>
> haha, no worries. I could have only said, I never noticed that problem.
> The main problem is the zig-zagging at lower resolution.
>
> On Sat, 1 May 2021 at 16:54, Gerd Petermann <
> gpetermann_muenchen at hotmail.com<mailto:gpetermann_muenchen at hotmail.com>>
> wrote:
> Hi all,
>
> sorry for the noise. Got confused by the special case with
> mkgmap:fast_road=yes in the default style.
>
> Gerd
>
> ________________________________________
> Von: Gerd Petermann <gpetermann_muenchen at hotmail.com<mailto:
> gpetermann_muenchen at hotmail.com>>
> Gesendet: Samstag, 1. Mai 2021 10:46
> An: Development list for mkgmap
> Betreff: AW: [mkgmap-dev] Request - set --reduce-point-density= for each
>       resolution
>
> Hi Felix,
>
> reg. low resolutions:
> I think there is also an error in mkgmap which filters e.g. large parts
> (almost all) of motorways at resolution 14.
>
> 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: Freitag, 30. April 2021 16:55
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] Request - set --reduce-point-density= for each
>       resolution
>
> sorry - patch has some typos as i was still playing around with values.
> here is a working version. These values I feel are good with 1.3 at
> commandline.
>
> On Fri, 30 Apr 2021 at 22:44, Felix Hartmann <extremecarver at gmail.com
> <mailto:extremecarver at gmail.com><mailto:extremecarver at gmail.com<mailto:
> extremecarver at gmail.com>>> wrote:
> I hardcoded a patch - as I was not sure someone is interested in it. This
> is doing the job - but I do feel others could profit as well. And yes I now
> understood how I could change this for a map starting at resolution 23 as
> well. I'm still not sure why do we not run the DP filter on resolution 24?
> I would image a very small value would give some improvement without
> visually changing anything.
>
> I haven't really looked at polygons yet - but my patch looks pretty good
> to me if you use a value of 1.3. So just as recommendation for default
> values. I feel the current default of 2.6 was exactly that low - because at
> resolution 23 a high value is really bad, while at lower resolutions there
> is a need for simplification. it's a bad compromise.
>
> On Fri, 30 Apr 2021 at 20:38, Gerd Petermann <
> gpetermann_muenchen at hotmail.com<mailto:gpetermann_muenchen at hotmail.com
> ><mailto:gpetermann_muenchen at hotmail.com<mailto:
> gpetermann_muenchen at hotmail.com>>> wrote:
> Hi Felix,
>
> you are probably right, the DP filter was not adapted to work with a map
> with resolution 23 as highest resolution. A quick change would be to
> disable the filter at level 0, similar to a map with max resolution 24.
> The --reduce-point-density sets the error distance for the Douglas-Peucker
> (DP) algorithm.
> If I got you right that's not enough for a map with levels = 0:24, 1:23,
> ... because you would want to use a rather small error distance for the
> first two layers and a higher value for the rest.  Sounds reasonable to me.
> Probably also for --reduce-point-density-polygon.
>
> I'll try to implement both.
>
> Gerd
>
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk<mailto:
> mkgmap-dev-bounces at lists.mkgmap.org.uk><mailto:
> 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><mailto:
> extremecarver at gmail.com<mailto:extremecarver at gmail.com>>>
> Gesendet: Mittwoch, 28. April 2021 05:03
> An: Development list for mkgmap
> Betreff: [mkgmap-dev] Request - set --reduce-point-density= for each
> resolution
>
> As I'm not sure everyone is following the other topic, I would like to ask
> to introduce the possibility to set different values for the DP filter
> based on resolution.
>
> Why is this important?
>
> a) maps which are produced with resolution 23 as highest resolution need
> to have a much lower level than subsequent resolutions.
> b) For resolution 23 and 22 a lower level makes sense - it is not needed
> as much here to speed up the gps device map drawing speed, while for lower
> resolutions like 18-21 a high level is really needed else map panning
> becomes painfully slow (usually basemap kicks in at 17).
>
> If I'm correct right now 2.6 at resolution 23 would be 5.4 at resolution
> 22, 10.8 at resolution 21 and so on. It's okay to keep that behaviour - but
> the value doubled just needs to be possible to be set for each resolution.
> It doesn't matter to me if we keep it like that or if we change the numbers
> than ourselves by resolution. Important thing is that it's possible to be
> set for each resolution
>
> c) maybe also introduce the possibility to set DP for resolution 24. I
> think a value of 0.3-0.6 could be worth it. I'm not sure if there were some
> problems preventing DP to be used at 24. However as by now I think mkgmap
> is able to produce routable maps starting at 23 instead of 24, those
> problems should be fixed...
> In general I think a map made for automotive use (car, motorcycle) would
> be fine using resolution 23 as a start instead of 24. Like Garmin City
> Navigator maps do. But then yes it's really important to not have a high DP
> value on resolution 23. Same as contourlines only maps which make sense at
> resolution 23 instead of 24.
>
> --
> Felix Hartman - Openmtbmap.org & VeloMap.org
>
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> mkgmap-dev at lists.mkgmap.org.uk>>
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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
>
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
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>

-- 
Felix Hartman - Openmtbmap.org & VeloMap.org
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