# [PATCHES] Small doc patch for area() function...

Small patch that adds some documentation for the area() function. Specifically, point out that intersecting points in a path will yield (most likely), unexpected results. Visually these are identical paths, but mathematically they're not the same. Ex:

area | plan
------ +----------------------------------------------------------------------- -------------------
-0 | ((0,0),(0,1),(2,1),(2,2),(1,2),(1,0),(0,0))
2 | ((0,0),(0,1),(1,1),(1,2),(2,2),(2,1),(1,1),(1,0),(0,0))

The current algorithm for area(PATH) is very quick, but only handles non-intersecting paths. I'm going to work on two other functions for the PATH data type that determines if a PATH is intersecting or not, and a function that returns the area() for an intersecting PATH. The intersecting area() function will be considerably slower (I think it's going to be O(n!) or worse instead of the current O(n), but that comes with the territory).

`-sc`

```Index: func.sgml
===================================================================
RCS file: /projects/cvsroot/pgsql-server/doc/src/sgml/func.sgml,v
retrieving revision 1.205
diff -u -r1.205 func.sgml
--- func.sgml   26 May 2004 18:35:31 -0000      1.205
+++ func.sgml   28 May 2004 04:49:43 -0000
@@ -5971,6 +5971,22 @@
as an array of two <type>point</> values.
</para>

+    <para>
+     The <function>area</function> function works for the types
+     <type>box</type>, <type>circle</type>, and <type>path</type>.
+     The <function>area</function> function only works on the
+     <type>path</type> data type if the points in the
+     <type>path</type> are non-intersecting.  For example, the
+     <type>path</type>
+     <literal>'((0,0),(0,1),(2,1),(2,2),(1,2),(1,0),(0,0))'::PATH</literal>
+     won't work, however, the following visually identical
+     <type>path</type>
+
<literal>'((0,0),(0,1),(1,1),(1,2),(2,2),(2,1),(1,1),(1,0),(0,0))'::PATH</literal>
+     will work.  If the concept of an intersecting versus
+     non-intersecting <type>path</type> is confusing, draw both of the
+     above <type>path</type>s side by side on a piece of graph paper.
+    </para>
+
</sect1>

```

PS Right now I'm developing on OS-X and there's a geometry regression test that's returning -0. FWIW

```*** ./expected/geometry.out     Fri Oct 31 19:07:07 2003
--- ./results/geometry.out      Thu May 27 22:16:58 2004
***************
*** 117,123 ****
| (5.1,34.5) | [(1,2),(3,4)]                 | (3,4)
| (-5,-12)   | [(1,2),(3,4)]                 | (1,2)
| (10,10)    | [(1,2),(3,4)]                 | (3,4)
!         | (0,0)      | [(0,0),(6,6)]                 | (-0,0)
| (-10,0)    | [(0,0),(6,6)]                 | (0,0)
| (-3,4)     | [(0,0),(6,6)]                 | (0.5,0.5)
| (5.1,34.5) | [(0,0),(6,6)]                 | (6,6)
--- 117,123 ----
| (5.1,34.5) | [(1,2),(3,4)]                 | (3,4)
| (-5,-12)   | [(1,2),(3,4)]                 | (1,2)
| (10,10)    | [(1,2),(3,4)]                 | (3,4)
!         | (0,0)      | [(0,0),(6,6)]                 | (0,0)
| (-10,0)    | [(0,0),(6,6)]                 | (0,0)
| (-3,4)     | [(0,0),(6,6)]                 | (0.5,0.5)
| (5.1,34.5) | [(0,0),(6,6)]                 | (6,6)```

`======================================================================`

```--
Sean Chittenden```
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