[postgis-users] Is there a better way for Finding Gaps/Sliver Holes?

[Martin Davis]

Yes, that technique only applies to polygonal coverages.

Your use case is not clear to me.  An example dataset might make that more
clear.

On Mon, May 2, 2022 at 11:40 AM Shaozhong SHI <shishaozhong at gmail.com>
wrote:

>
>
> On Mon, 2 May 2022 at 19:05, Martin Davis <mtnclimb at gmail.com> wrote:
>
>> That blog post does provide useful queries for finding polygon overlaps
>> and gaps.
>>
>> Overlaps are found via testing if polygon interiors intersect, using the
>> DE-9IM relate mask 2********.
>>
>> Gaps are found by identifying holes in the union of the set of polygons.
>> One issue with this is that computing the union of large datasets can be
>> slow.  Lars' solution provides some ideas for dealing with this.
>>
>>
>> I think that matters are rather more complex than this.
>
> For instance, I found 2 lines meet with each other at both ends.  In this
> case, 2 intersections are both a point.  One will find two lines form an
> enclosed area.
>
> When 2 lines intersect or meet/touch more than 2 times, intersection will
> return more than 2 points.   For instance, when two lines meet at 3 points,
> one would get 2 gap polygons.
>
> Given 2 zigzagging lines, how to write a function to return overlaps and
> gaps is an interesting matter.
>
> Regards,
>
> David
>
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