[mkgmap-dev] mapnik TYP, forest and wetland

Mon Nov 2 18:27:39 GMT 2020

Hi Karl

The default draworder is probably device specific. It has been found
that most polygon have the same priority, with, for some reason, just a
few different - I think there is a wiki page on this.

Without --order-by-decreasing area, the output order is as good as
random, so one wetland might be over a forest, another underneath it.
Even more interesting, on some devices, you might see a feature for a
few seconds but then it will be overwritten by another with the same or
higher draworder. This can be very obvious if you scroll across a map. 
My eTrex HCx did this because it started to display things as soon as
possible. My eTrex 30x just shows a blank bit of screen until it is
sure it has found all the features to display.

Ticker

On Mon, 2020-11-02 at 19:05 +0100, 7770 wrote:
> The default garmin style (no TYP added), does draw the wetland in the
> forest.
> Actually it seems to draw it over the forest (no transparency).
> 
> This occurs even without the --order-by-decreasing-area.
> 
> Regards
> Karl
> 
> 
> On måndag 2 november 2020 kl. 18:26:42 CET 7770 wrote:
> > Hi.
> > No worries. It just means that the map maker must be more thorough.
> > I can see that some makers take this into consideration, but others
> > have
> > not. In effect it means that data is processed, but in the end
> > cannot be
> > shown if the TYP is applied at the end.
> > 
> > --order-by-decreasing-area, according to the documentation only
> > works if the
> > polygons have the same draw order, which these two do not by
> > default.
> > 
> > 
> > Regards
> > Karl
> > 
> > On måndag 2 november 2020 kl. 18:18:11 CET Ticker Berkin wrote:
> > > Hi
> > > 
> > > I understand that many users prefer a fixed order of rendering
> > > based on
> > > the polygon type, and this is part of the definition of
> > > mapnik.txt and
> > > seems to be the 'Garmin' way of doing things.
> > > 
> > > If there is a consensus that the draworder should be different,
> > > then
> > > make it so. I'd think that wetland and forest should be the same
> > > as the
> > > other large-area landuse polygons, with priority 2
> > > 
> > > Option --order-by-decreasing-area removes the need to make any of
> > > these
> > > fixed rendering choices but at the cost of an increase in map
> > > size and,
> > > possibly, mkgmap execution time. It works for MapSource and
> > > BaseCamp
> > > and Garmin devices I've encountered, but not for GPSMapEdit.
> > > If used, it is best to set the draworder for all real polygons to
> > > the
> > > same value.
> > > 
> > > It is a shame that the TYP.txt file has to contain everything
> > > (draworder, translations and object colour/icons). It would be
> > > beneficial it they could separated and the wanted variants of
> > > components supplied to mkgmap.
> > > 
> > > Ticker
> > > 
> > > On Mon, 2020-11-02 at 16:55 +0100, 7770 wrote:
> > > > Hi.
> > > > 
> > > > In the example mapnik.txt TYP file, the draworder of the
> > > > polygons for
> > > > woods/
> > > > forest 0x50 and wetland 0x51 are given like this:
> > > > 
> > > > [_drawOrder]
> > > > ..
> > > > Type=0x050,3
> > > > ..
> > > > Type=0x051,2
> > > > ..
> > > > [End]
> > > > 
> > > > 
> > > > When compiling a map, this means that wetlands in forests are
> > > > not
> > > > visible if
> > > > this TYP is used.
> > > > 
> > > > I tried makling a map using the same draworder
> > > > Type=0x050,2
> > > > Type=0x051,2
> > > > plus using the option --order-by-decreasing-area
> > > > 
> > > > This makes the wetland visible in forests.
> > > > I could not see any negative impacts of this in the areas which
> > > > i
> > > > checked (a
> > > > few in Sweden and Norway). Wetlands over other areas seems to
> > > > work
> > > > fine as
> > > > well.
> > > > 
> > > > Do you think such a change would be of help or is there a great
> > > > risk
> > > > that this
> > > > type of change would impact negatively on the drawing of the
> > > > maps?
> > > > 
> > > > 
> > > > 
> > > > Regards
> > > > Karl
> > > > 
> > > > 
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> > > 
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> 
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