Hi Gerd,
a good algorithm to find a point for the --add-pois-to-areas option
would be to use the straight skeleton algorithm
(http://www.mkgmap.org.uk/pipermail/mkgmap-dev/2011q3/012394.html). This
might be used to find a point with maximum distance to the border of a
polygon. Anyhow it seems to be a complex algorithm so maybe not the
ideal solution for mkgmap.
WanMil
Hi Steve,
Steve Ratcliffe wrote
On 03/01/15 08:15, Gerd Petermann wrote:
@Steve:
The routine was initially created for the --check-roundabouts option.
Later it was also used for --add-pois-to-areas and the --housenumbers
option.
I got the impression that it might be better to calculate the center
of the way bbox for those two, I am not so sure about the roundabout
code.
What do you think?
Seems like the current method would tend to place the point near the
most complex part of the boundary. This may not be bad, I would have
to see lots of real examples to be sure.
Yes, correct. I compared these three algos:
1) the existing
2) my patched one
3) center of bbox
For complex shapes (many points), 1) and 2) produce almost equal
results, and in fact the point was more often within the shape.
For simple polygons like small parks, buildings, etc. 1) is worst,
2) is better and 3) is best.
My conclusion: the patch is a simple and good improvement,
for housenumber location calculation maybe it would be better to use
algo 3).
Steve Ratcliffe wrote
Anyway there are no easy (or even any difficult!) methods that work in
all cases, so I would just keep it as it is and perhaps should the
calculated point be outside the box, move it to the closest point
inside.
I already looked at the link provided by Andrzej.
If I got that right, we have two different problems regarding
the generated POI:
We calculate it once for the whole polygon, before clipping
it to the bbox of the tile, and it might be outside of the polygon
as well as outside of the bbox.
This brought me back to the non-rectangular tile problem and I stop
searching for a solution for the POI problem.
Reg. non-rectangular tiles: I fear we can't use any of the existing
algos in mkgmap to implement this, I'll report details in a different post.
Gerd
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