[mkgmap-dev] There is not enough room in a single garmin map for all the input data

Mon Dec 31 00:25:35 GMT 2012

Hi

A large polygon is split up into many smaller ones.  For a tile with a
large area of sea there will therefore be many more polygons in the img
file than you would expect from the number of nodes on the coastline.
So that is one problem. The polygons fragments will be roughly the
same size and so it would be possible to calculate and allow for them
in theory.

The polygon is sliced into fragments with horizontal and vertical
lines.  This is the reason for the
PreserveHorizontalAndVerticalLinesFilter; you mustn't allow the
straight lines of the polygon fragments to be smoothed in any way, or
else they won't form the complete polygon any more.  We used to get
triangular shaped pieces of sea. On the other hand a different
smoothing algorithm was used in the past and so perhaps the new one
does not mangle straight lines.

[As a separate issue, I don't know if the Douglas Peucker algorithm is
the most suitable one to smooth polygons and if anyone wants to look
into that, it would be great]

> The base class OsmHandler has a method addCoordToWay(..). In this method
> the highwayCount is increased always - no matter if it is a way or not.
> This was introduced by merging the way-closing branch.
> So Steve should have a look on it. I think that's not intended.

The fact that highwayCount is incremented always is harmless in itself
and necessary, since at that point we do not know what is a road and
what isn't (highwayCount is not a great name, except that it is not
used for ordinary lines). Obviously we shouldn't be doing any specific
road processing later on and that needs looking into, certainly
shouldn't be calling removeShortArcsByWhatever() on anything that
isn't a road.  That whole area of the code is now quite old and was
written before we knew how routing worked so we might want to
rearrange it differently now.

> Osm5XmlHandler.startInNode checks for a tag mkgmap:on-boundary. If that
> is set the highwayCount is increased. So far so good but this is not
> performed in the PBF and o5m handler. So maybe this can be removed or
> must be added to the other handlers too.

This is to support the case where a splitter-like program creates an
extract that is exactly trimmed to the boundary and has created its
own boundary nodes. I don't think that anyone does this. However
it's not wrong and could be added the other handlers if someone does
use it.

..Steve