[OSM-dev] multipolygon relation and non-closed ways

[Jukka Rahkonen]

Martin Koppenhoefer kirjoitti:
> 2012/10/14 Frederik Ramm <frederik at remote.org>:
>> Personally I don't consider the "8" shapes valid - and I don't think
>> there's
>> a difference between the one with a node in the middle and the one
>> without.
>> I don't consider the "inner ring touching outer ring in single point"
>> case
>> to be valid either.
>
>
> IMHO the second case would also be bad mapping if it was technically
> valid. There are no such situations in real life and I cannot imagine
> a situation where this would not be a bad abstraction.

Hi,

The inner triangle could be a cadastral parcel inside another cadastral
parcel sharing only one common landmark. For sure such cases exist in real
life. Drawing this as one outer ring touching itself in one point seems to
be invalid for JTS (self-intersection) while drawing an inner ring
touching outer ring at one point is OK for JTS.

OpenJUMP is a good tool for testing what JTS thinks about validity. Set
Snap to vertises and Prevent edits leading to invalid geometry options on
from the settings and start digitizing.

-Jukka Rahkonen-

> cheers,
> Martin
>
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