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 - 1.205
+++ func.sgml 28 May 2004 04:49:43 -
@@ -5971,6 +5971,22 @@
as an array of two typepoint/ values.
/para
+para
+ The functionarea/function function works for the types
+ typebox/type, typecircle/type, and typepath/type.
+ The functionarea/function function only works on the
+ typepath/type data type if the points in the
+ typepath/type are non-intersecting. For example, the
+ typepath/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
+ typepath/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 typepath/type is confusing, draw both of the
+ above typepath/types 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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