[mkgmap-dev] filters for shapes

Wed Feb 6 10:54:13 GMT 2013

Hi,

the current filter chain for shapes is a bit confusing for me:
- We start with PreserveHorizontalAndVerticalLinesFilter which uses the
original coords (in map units)
to preserve endpoints of vertical and horizontal lines.
- Next we use the RoundCoordsFilter which rounds the coords according to the
desired resolution
For low resolutions, many small shapes are rounded to a single point. Only
when the remaining line has at least two points we continue either with the
SizeFilter or with the DouglasPeuckerFilter (if they are not disabled)

Only the DouglasPeuckerFilter cares about the preserved flag, so I think the 
PreserveHorizontalAndVerticalLinesFilter should be moved directly before it
so that it checks
only the rounded coords.

I also wonder why we use the PreserveHorizontalAndVerticalLinesFilter for
lines that are
not shapes. The filter was added with a comment regarding polygons only.

Ciao,
Gerd

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