[mkgmap-dev] [PATCH] alpha patch for simplifying ways and reducing img size

Fri Feb 20 12:07:54 GMT 2009

Hi Johann,

> Find attached an patch (usable on R915), which reduces the point density 
> of ways and roads to reduce the filesize of the resulting img file.
> It does it by using the douglas peucker algorithm. With this algorithm 
> it is possible to set a max error distance and the resulting line will 
> have filtered out all points without any points outside this distance band.
> For an exact explanation consult wikipedia.
> 
> I tried it with an error distance of 10m. Higher distances don't gain 
> much more.
> The saving is in some areas with bad osm data (useless high point 
> density) up to 25%.
> In general it saves only 5% in file size.
> 
> Consider this patch as an alpha release, which should only show the 
> possibilities.
> For the release it will need at least an option at the commandline for 
> setting the error distance.
> 
> Also I'm not sure, if the StyledConverter.java is the correct file for 
> this patch. I've seen there is some filter infrastructure in the mkgmap 
> project, but I've no idea how to use it.

Personally, I would not want this feature enabled by default. Why not
add an option that turns it on and also can be used to specify the error
distance. e.g. --reduce-point-density to turn the feature on and
--reduce-point-density=NUM to turn it on and specify the, non-default,
error distance. The --frig-roundabouts option does a similar thing.

Also, is it a feature that should be available for the mp input as well as
the osm?

Cheers,

Mark