No, buildings are not the most interesting. I once generalized all buildings in 
Denmark. It only reduced the storage by maybe 5%, at the high cost of heavily 
distorting a large number of them. Most buildings in OSM are in fact already in 
their most generalized state: just 4 nodes. Unless you think triangles is a 
suitable representation ;-). Besides, buildings are only shown at high zoom, 
while generalization is most needed and beneficial at low zoom. Lastly, most 
vector generalization algorithms are primarily designed and effective for 
rather smooth and node rich data, like a stream-digitized feature, neither of 
which relates to square buildings. Hence  i consider generalizing buildings 
largely senseless.




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Van: Tomas Straupis 


Verstuurd: maandag 16 april 11:48 


Onderwerp: Re: [OSM-dev] Generalisation 


Aan: Openstreetmap Dev list 






2018-04-16 11:34 GMT+03:00 Martin Koppenhoefer wrote: > There are some 
precomputed / extracted data files though, some of which > contain generalized 
(simplified) data. These are all "external" sources: > Ok, so this is natural 
polygon generalisation. Looking at https://github.com/imagico/coastline_gen the 
method used is to rasterise, process and then vectorise back. I wonder if that 
is better/faster than full vector way: st_clusterwithin, st_union, 
st_buffer(positiveN), st_buffer(negativeN+M), st_buffer(positiveM) with a 
seasoning of st_simplifypresevetopology according to taste. > Another aspect is 
filtering: osm-carto removes features when they would be > very small (pixels 
at a given zoom level) and lead to "noise". Filtering (selection) is 
technically also a generalisation. But you need to group and probably 
amalgamate them before deciding that it is "too small". For example if we have 
a lot of small patches of forest close together (say 1000 patches of 10x10m 
with distance between patches of 1m) you would want to amalgamate them to one 
large forest, not to get rid of them all. Ways and especially buildings are the 
most interesting (difficult) part :-) P.S. GRASS claims to be doing 
displacement and way selection 
(https://grasswiki.osgeo.org/wiki/V.generalize_tutorial) -- Tomas 
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