I think polygons can be higher value except at level=0. In general I think it is better to have a bit higher values for higher levels. However then again lower for the overview map. However if the improve-overview filter chain would apply in general - then values need to be much lower. There is very aggressive filtering in comparison.

-x-simplify-filter-line-errors=23:2.6,22:4.2,21:5.4,20:6,19:7,18:7.5,17:5.2,13:5.2

--x-simplify-filter-polygon-errors=23:3.6,22:7,21:6,20:9,17:2.6

Why do we need higher values for resolutions far zoomed out? Most garmin GPS devices are pretty slow if zoomed out far - so heavily filter those polygons/lines to get decent speed. PC/desktop are fast enough for even complicated overview map - so that one should be optimized for best visual quality. Some filtering is needed usually however else Asia continent map or Europe continent map would break the img size limit.

This is what I am using now - and it works pretty well. Also the polygon size limits I feel the following is way better than default. Tiny dots look more like errors than help much:

--polygon-size-limits="24:12, 23:14, 22:14, 21:20, 20:20, 19:20, 18:20, 17:20, 16:20, 15:20, 14:20, 13:25"

On Mon, 14 Jun 2021 at 23:32, Mike Baggaley <mike@tvage.co.uk> wrote:

Hi Gerd,

I think the original documentation for --reduce-point-density and
--reduce-point-density-polygon could do with some improvement. It also seems
bizarre to have a recommended value that is not the default. Is 2.6 the
default if --reduce-point-density is specified without a value, or is it
also the default if the option is not specified? Are the units metres? Is
the distance the same no matter what resolution is used, or does the
distance increase at lower resolution? If the former, wouldn't it be better
to increase by a factor of 1.414 at successive resolutions? Would this be
sufficient to not need to be able to specify individual values for
resolutions?

I'm not keen on having two very differently named options that basically
achieve the same aim and suggest that it would be better to simply extend
the existing --reduce-point-density options with
--reduce-point-density=value|resolution:value[,...] or even better
--reduce-point-density=value[,...] where the first value applies to the
first used resolution and so on, with the last value being scaled for any
further resolutions that have not had a value specified.

Is there a reason why polygons need different values than lines? Shouldn't
reduce-point-density-polygon default to the reduce-point-density value?

I note that although the documentation belongs to the low-res-branch, it is
showing up on the mkgmap command line web page.

Regards,
Mike

-----Original Message-----
From: Gerd Petermann [mailto:GPetermann_muenchen@hotmail.com]
Sent: 14 June 2021 07:43
To: mkgmap-dev@lists.mkgmap.org.uk
Subject: [mkgmap-dev] Documentation for the new Douglas-Peucker options in
low-res-opt branch

Hi all,

I've now added documentation for these new options, see:
https://www.mkgmap.org.uk/websvn/diff.php?repname=mkgmap&path=%2Fbranches%2F
low-res-opt%2Fresources%2Fhelp%2Fen%2Foptions&rev=4775&peg=4775

Is it clear enough?
I think the recommend value --reduce-point-density-polygon=8 is far too high
at low resolutions. Should this be changed?

Together with the new --improve-overview option this branch version can
produce much better results for the lower resolutions.

Gerd

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