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

[Shaozhong SHI]

How about each line gets split into segments.  .  Each segment is
constructed with two points (current and next points.
Then, calculate bearing/azimuth
Then, determine whether it is clockwise or counter-clockwise.

Can this be done?

Regards,

David

On Wed, 16 Feb 2022 at 20:39, Marcin Mionskowski <
mionskowskimarcin at gmail.com> wrote:

> 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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