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List: postgis-users
Subject: Re: [postgis-users] function to check if a polygon is convex
From: Martin Davis <mtnclimb () gmail ! com>
Date: 2022-03-02 22:03:34
Message-ID: CAK2ens10XDLazBc45rW9moJPiRTBmiGLVm=NzkPctdQY8oa-PA () mail ! gmail ! com
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Yes, that's a way to check if a polygon is convex. Not the most efficient,
but currently there's no more direct way (pretty sure).
On Wed, Mar 2, 2022 at 1:38 PM B H <hemantbist@gmail.com> wrote:
>
> select st_equals(st_convexhull(wkb_geometry), wkb_geometry) is true for
> all st_isvalid convex polygons I tried on).
> Is this a correct way to check for convexity of the polygon?
>
>
> On Wed, Mar 2, 2022 at 1:15 PM B H <hemantbist@gmail.com> wrote:
>
> > Hi,
> > How do I check if the polygon is convex in postgis?
> >
> > Things I have tried before sending this email
> > I could not find any function like st_is_convex.
> > I searched in google but I could not find any user defined postgres
> > function to check for convexity of polygon either.
> > select st_convexhull(wkb_geometry) = wkb_geometry -- this returns false
> > for convex polygons also.
> >
> > Other libraries e.g. CGAL seem to have it. So I am hoping that something
> > is already available in postgis that I am missing.
> >
> > https://doc.cgal.org/Manual/3.1/doc_html/cgal_manual/Partition_2_ref/Function_convex_partition_is_valid_2.html
> > Best,
> > HB
> >
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[Attachment #5 (text/html)]
<div dir="ltr"><div>Yes, that's a way to check if a polygon is convex. Not the \
most efficient, but currently there's no more direct way (pretty \
sure).</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, \
Mar 2, 2022 at 1:38 PM B H <<a \
href="mailto:hemantbist@gmail.com">hemantbist@gmail.com</a>> \
wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px \
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div \
dir="ltr"><div><br></div>select st_equals(st_convexhull(wkb_geometry), wkb_geometry) \
is true for all st_isvalid convex polygons I tried on).<div>Is this a correct way \
to check for convexity of the polygon?<br><div><br></div></div></div><br><div \
class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Mar 2, 2022 at 1:15 PM \
B H <<a href="mailto:hemantbist@gmail.com" \
target="_blank">hemantbist@gmail.com</a>> wrote:<br></div><blockquote \
class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid \
rgb(204,204,204);padding-left:1ex"><div dir="ltr">Hi,<div>How do I check if the \
polygon is convex in postgis?</div><div><br></div><div>Things I have tried before \
sending this email</div><div> I could not find any function like \
st_is_convex.</div><div>I searched in google but I could not find any user defined \
postgres function to check for convexity of polygon either.</div><div>select \
st_convexhull(wkb_geometry) = wkb_geometry -- this returns false for convex \
polygons also.<br></div><div><br></div><div>Other libraries e.g. CGAL seem to have \
it. So I am hoping that something is already available in postgis that I am \
missing.</div><div><a \
href="https://doc.cgal.org/Manual/3.1/doc_html/cgal_manual/Partition_2_ref/Function_convex_partition_is_valid_2.html" \
target="_blank">https://doc.cgal.org/Manual/3.1/doc_html/cgal_manual/Partition_2_ref/F \
unction_convex_partition_is_valid_2.html</a><br></div><div>Best,</div><div>HB</div></div>
</blockquote></div>
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</blockquote></div></div>
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