[mkgmap-dev] small issue with Way.getCofG()

Sun Jan 4 11:40:52 GMT 2015

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
>
>
>
>
> --
> View this message in context: http://gis.19327.n5.nabble.com/small-issue-with-Way-getCofG-tp5828821p5828952.html
> Sent from the Mkgmap Development mailing list archive at Nabble.com.
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
>