[postgis-users] ST_NPoints from polygons

[Etienne B. Racine]

Thanks!

Le lun. 1 juil. 2019 à 11:25, Martin Davis <mtnclimb at gmail.com> a écrit :

> Yes, that is correct.
>
> As per the Simple Features for SQL standard, Linear Rings include a
> closing point which is equal to the start point, and all points are
> included in the count.  Polygons are made up of rings, so inherit this
> behaviour.
>
> On Mon, Jul 1, 2019, 4:46 AM Etienne B. Racine <etiennebr at gmail.com>
> wrote:
>
>>
>> Hi list,
>>
>> I'm implementing postgis compatible functions for R, so I wanted to make
>> sure I had the right behavior. I wanted to check that the behavior of
>> ST_NPoints was consistent with expectations.
>> SELECT ST_NPoints('POLYGON((0 0, 1 1, 2 0, 0 0))'::geometry);
>> #>  st_npoints
>> #> ------------
>> #>           4
>> I would have expected that the repeated vertex wouldn't be counted (a
>> triangle would have 3 vertices). The doc (*Return the number of points
>> in a geometry*) seems to imply that the behavior is correct though,
>> since a point isn't necessarly a vertex; but it still leaves room to
>> interpretation.
>>
>> Etienne
>>
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