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

[Shaozhong SHI]

Sorry, I have not got any example dataset.

If some one can create a schematic/mock-up data set, we can test our way
forward.

I am looking into the fundamentals of data testing and quality assurance
techniques by using PostGIS.

Regards,

David

On Mon, 2 May 2022 at 19:57, Martin Davis <mtnclimb at gmail.com> wrote:

> 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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