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[mkgmap-dev] Documentation improvements for sea processing,

From Gerd Petermann gpetermann_muenchen at hotmail.com on Fri Feb 19 09:21:41 GMT 2021

Hi all,

- reg. --add-pois-to-lines (and also ----add-pois-to-areas)
I think the texts (and of course the option names) are misleading. The program doesn't generate "POI", it just generates additional nodes with special tags and the point rules decide what to do with those nodes.
I noticed this because of the new text "An extra point added by mkgmap at the middle of the line".
Really, mkgmap adds a new node for all existing nodes of the unclosed way AND one extra node for the calculated middle of the way. Some of the added nodes may be filtered, e.g. when two consecutive "inner" nodes have the same Garmin position.
I think the most important thing about nodes created by  the --add-pois-to-lines option is that the user probably has to add rules to ignore most of those nodes.

- Reg. "=== Sea Processing options ==="
I don't like the word "either" in this section. This implies that you cannot use --precomp-sea together with --generate-sea while the text for --precomp-sea says you can.

- The --generate-sea option can always be used to overwrite these defaults:

The default tag natural=land tag is also used in the precomp-sea data, and e.g. generate-sea: land-tag=natural=background can be used to change that. No idea why, found this option in the "Openfietsmap full" style together with these polygon rules:
natural=land [0x27 resolution 20]
natural=background [0x010100 resolution 12]

- I don't understand the sentence "Must be used in conjunction with the --generate-sea option." for --coastlinefile option. I guess this only applies when data like that in "gbcoastline-unfixed.zip" is used.

- I think the docu for --precomp-sea should point out that one can download that data from http://www.mkgmap.org.uk/download/mkgmap.html  and that it typically is the best option (I don't know any good alternative)
I see no need for a normal user to compile precomp-sea data, but the needed steps are shown in https://wiki.openstreetmap.org/wiki/Mkgmap/help/options#generating_precompiled_sea_yourself


Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
Gesendet: Mittwoch, 17. Februar 2021 11:33
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] Documentation improvements for sea processing,

Hi Mike & Gerd

No problems with this.

Concerning *-sea-sectors. My reading of the documentation implies
extend-sea-sectors and no-sea-sectors are alternatives. The
comprehension difficulty is because of the naming of 'extend-sea
-sectors', which are very different from the 'sea-sectors' that 'no-sea
-sectors' stops. 'sea-sectors' isn't a good name either because they
could be 'land-sectors'. Probably not worth thinking about this any


On Tue, 2021-02-16 at 20:23 +0000, Mike Baggaley wrote:
> Hi Gerd,
> Please find attached a patch to improve the documentation of sea
> processing
> plus minor changes to --add-pois-to-lines.
> I note that extend-sea-sectors says  "Adds a point so coastline
> reaches the
> nearest tile boundary. This implies no-sea-sectors". But no-sea
> -sectors
> disables the generation of sea sectors when the coastline fails to
> reach the
> tile's boundary, so I would have thought that extend-sea-sectors is
> an
> alternative action and would imply that no-sea-sectors is off.
> Cheers,
> Mike
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> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
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