7/12/2013 12:18 AM, Christoph Hormann wrote:
Could you explain in what ways this is the case. Since different types
of labels are shown in various maps direct comparison is difficult.
You seem to very well avoid overlaps between labels and none the less
you are able to put quite a lot of them on the map but non-label
feature do not appear to play a role in label placement and there are
some strange priorities. Is the algorithm available as open source?
Greetings,
Avoiding of overlaps in map labeling is a constraint that is necessary.
We can compare the map labeling on osm.org and on our map with the help
of the list of cartographic rules for point-feature labeling.
For example, they are:
* R1. *Type arrangement should reflect the classification, importance
and hierarchy of objects.
*R2.*The lettering to the right and slightly above the symbol is
prioritized.
*R3.*Names of coastal settlements should be written in water.
*R4.*Label should be placed completely on the land or completely on the
water surface.
*R5. *Names should not be too close to each other
*R6.*Labels should not be excessively clustered nor evenly spread out.
*R7. *Each label should be easily identified with its point-feature.
Ambiguous relationships between symbols and their names must be avoided.
*R8. *Label should not overlap other significant features of the
cartographic background or do it as little as possible.
As far as I know Mapnik and other open-source software take into account
only the rules R1, R2 and R5 (partially, returns labels that are evenly
spread out, example - http://maps.skobbler.com/on z11).
And the "greedy" algorithm that is utilized to solve the label placement
problem returns rather poor approximation to the optimum as there is no
backtracking.
Is the algorithm available as open source?
Unfortunately, the algorithm currently is not open-source, but the model
that we elaborated and used will be published as a journal paper within
the next few months.
All the best,
Maxim Rylov
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