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From: Tom Lane <tgl@sss.pgh.pa.us>
To: skalee@gmail.com
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: Chapter "8.8 Geometric Types" of documentation could contain more details
Date: Wed, 03 Jul 2024 15:45:18 -0400
Message-ID: <3282371.1720035918@sss.pgh.pa.us> (raw)
In-Reply-To: <172000045661.706.1822177575291548794@wrigleys.postgresql.org>
References: <172000045661.706.1822177575291548794@wrigleys.postgresql.org>

PG Doc comments form <noreply@postgresql.org> writes:
> Hi, I am writing to suggest a couple of clarifications to "8.8. Geometric
> Types" documentation chapter.

Fair points.  I am not really eager to say explicitly here that the
set of available functions varies for the different types: that seems
pretty self-evident.  But your other ideas are good.

I also noted while looking at this that table 8.20 is flat out wrong
about the storage size of "line" values: they are 24 bytes each not
32.  (This can be confirmed from pg_type.typlen or by looking at
struct LINE in the source code.)

How about the attached?

			regards, tom lane

Attachments:

  [text/x-diff] geometric-types-doc-improvement.patch (1.5K, ../3282371.1720035918@sss.pgh.pa.us/2-geometric-types-doc-improvement.patch)
  download | inline diff:
diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index 6646820d6a..a693424a69 100644
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -3369,7 +3369,7 @@ SELECT person.name, holidays.num_weeks FROM person, holidays
        </row>
        <row>
         <entry><type>line</type></entry>
-        <entry>32 bytes</entry>
+        <entry>24 bytes</entry>
         <entry>Infinite line</entry>
         <entry>{A,B,C}</entry>
        </row>
@@ -3413,6 +3413,11 @@ SELECT person.name, holidays.num_weeks FROM person, holidays
      </tgroup>
     </table>
 
+   <para>
+    In all these types, the individual coordinates are stored as
+    <type>double precision</type> (<type>float8</type>) numbers.
+   </para>
+
    <para>
     A rich set of functions and operators is available to perform various geometric
     operations such as scaling, translation, rotation, and determining
@@ -3607,6 +3612,14 @@ SELECT person.name, holidays.num_weeks FROM person, holidays
      within it, while a path is not.
     </para>
 
+    <para>
+     An important implementation difference between polygons and closed
+     paths is that the stored representation of a polygon includes its
+     smallest bounding box.  This speeds up certain search operations,
+     although computing the bounding box adds overhead while constructing
+     new polygons.
+    </para>
+
     <para>
      Values of type <type>polygon</type> are specified using any of the
      following syntaxes:

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  To: pgsql-docs@postgresql.org
  Cc: tgl@sss.pgh.pa.us, skalee@gmail.com, pgsql-docs@lists.postgresql.org
  Subject: Re: Chapter "8.8 Geometric Types" of documentation could contain more details
  In-Reply-To: <3282371.1720035918@sss.pgh.pa.us>

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