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Diffstat (limited to 'contrib/seg/README.seg')
| -rw-r--r-- | contrib/seg/README.seg | 20 |
1 files changed, 12 insertions, 8 deletions
diff --git a/contrib/seg/README.seg b/contrib/seg/README.seg index e738f180e8a..9e741756c33 100644 --- a/contrib/seg/README.seg +++ b/contrib/seg/README.seg @@ -214,7 +214,7 @@ have just 2 significant digits. USAGE ===== -The access method for SEG is a GiST (gist_seg_ops), which is a +The access method for SEG is a GiST index (gist_seg_ops), which is a generalization of R-tree. GiSTs allow the postgres implementation of R-tree, originally encoded to support 2-D geometric types such as boxes and polygons, to be used with any data type whose data domain @@ -236,23 +236,27 @@ The operators supported by the GiST access method include: [a, b] >> [c, d] Is right of [a, b] is occurs entirely to the right of [c, d]. - [a, b] >> [c, d] is true if b > c and false otherwise + [a, b] >> [c, d] is true if a > d and false otherwise -[a, b] &< [c, d] Over left +[a, b] &< [c, d] Overlaps or is left of - The segment [a, b] overlaps the segment [c, d] in such a way - that a <= c <= b and b <= d + This might be better read as "does not extend to right of". + It is true when b <= d. -[a, b] &> [c, d] Over right +[a, b] &> [c, d] Overlaps or is right of - The segment [a, b] overlaps the segment [c, d] in such a way - that a > c and b <= c <= d + This might be better read as "does not extend to left of". + It is true when a >= c. [a, b] = [c, d] Same as The segments [a, b] and [c, d] are identical, that is, a == b and c == d +[a, b] && [c, d] Overlaps + + The segments [a, b] and [c, d] overlap. + [a, b] @ [c, d] Contains The segment [a, b] contains the segment [c, d], that is, |