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

Fri Apr 30 15:55:47 BST 2021

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>
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> 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> im Auftrag von
>> Felix Hartmann <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
>>
>> _______________________________________________
>> mkgmap-dev mailing list
>> mkgmap-dev at lists.mkgmap.org.uk
>> https://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
>>
>
>
> --
> Felix Hartman - Openmtbmap.org & VeloMap.org
>
>

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