From b0f2d681bdfd6a5b3e90d092f9d924f943b4fc5f Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 10 Nov 2010 16:51:39 -0500
Subject: [PATCH] Fix line_construct_pm() for the case of "infinite" (DBL_MAX)
slope.
This code was just plain wrong: what you got was not a line through the
given point but a line almost indistinguishable from the Y-axis, although
not truly vertical. The only caller that tries to use this function with
m == DBL_MAX is dist_ps_internal for the case where the lseg is horizontal;
it would end up producing the distance from the given point to the place
where the lseg's line crosses the Y-axis. That function is used by other
operators too, so there are several operators that could compute wrong
distances from a line segment to something else. Per bug #5745 from
jindiax.
Back-patch to all supported branches.
---
src/backend/utils/adt/geo_ops.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/src/backend/utils/adt/geo_ops.c b/src/backend/utils/adt/geo_ops.c
index f3b6a389ff4..8a99df1356c 100644
--- a/src/backend/utils/adt/geo_ops.c
+++ b/src/backend/utils/adt/geo_ops.c
@@ -1072,13 +1072,20 @@ line_construct_pm(Point *pt, double m)
{
LINE *result = (LINE *) palloc(sizeof(LINE));
- /* use "mx - y + yinter = 0" */
- result->A = m;
- result->B = -1.0;
if (m == DBL_MAX)
- result->C = pt->y;
+ {
+ /* vertical - use "x = C" */
+ result->A = -1;
+ result->B = 0;
+ result->C = pt->x;
+ }
else
+ {
+ /* use "mx - y + yinter = 0" */
+ result->A = m;
+ result->B = -1.0;
result->C = pt->y - m * pt->x;
+ }
#ifdef NOT_USED
result->m = m;
--
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