# [postgis-users] Are there script examples for determine where vertices run clockwise or anti-clockwise?

Marcin Mionskowski mionskowskimarcin at gmail.com
Wed Feb 16 12:39:01 PST 2022

```It doesn't make sense for lines.
Imagine LINESTRING(1 0,1 1) - which "part of a square" is this i.e. where
is "the center of the square": (1) 0.5,0.5 or (2) 1.5,0.5?
If (1) it's CCW, if (2) CW.

śr., 16 lut 2022 o 21:29 Shaozhong SHI <shishaozhong at gmail.com> napisał(a):

> The problem now is that I can not find anything for lines.
>
> Anything like ST_IsPolygonCW|ST_IsPolygonCCW for lines for instance,
> something like ST_IsLineCW|ST_IsLineCCW.
>
> Regards,
>
> David
>
> On Wed, 16 Feb 2022 at 19:43, Marcin Mionskowski <
> mionskowskimarcin at gmail.com> wrote:
>
>> Assuming simple polygons, composed from exterior ring only (i.e. no
>> multipolygons), I think that you are looking for a function
>> {ST_IsPolygonCW|ST_IsPolygonCCW}.
>>
>> Greetings,
>> Marcin
>>
>> śr., 16 lut 2022 o 19:55 Imre Samu <pella.samu at gmail.com> napisał(a):
>>
>>> > how vertices run?  clockwise or anti-clockwise?
>>>
>>> maybe the:
>>> https://postgis.net/docs/ST_Angle.html  *"Computes the clockwise angle
>>> between two vectors."*
>>> or https://postgis.net/docs/ST_Azimuth.html
>>>
>>> regards,
>>>  Imre
>>>
>>>
>>> Shaozhong SHI <shishaozhong at gmail.com> ezt írta (időpont: 2022. febr.
>>> 16., Sze, 17:06):
>>>
>>>> Can we use PostGIS to find out how vertices run?  clockwise or
>>>> anti-clockwise?
>>>>
>>>> Regards,
>>>>
>>>> David
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