When I was debugging my invalid geometry problem, I needed to select a
small area to view. The data is divided up into 1 degree tiles (it's
the SRTM SWBD shapefiles imported). I figured selecting by whole
integer degrees would be simple to deal with.
I started with st_overlaps(), as it was mentioned in the wiki I think,
or somewhere online (this was a few weeks ago, and don't remember the
details). But it was not selecting very much at all in a large area.
I looked at the PostGIS documentation to see what other functions
would work, but their descriptions are not plain english and and tried
them all. And there was a pointer to:
http://lin-ear-th-inking.blogspot.com/2007/06/subtleties-of-ogc-covers-spatial.html
that helped a little. But none of the ones I tried gave me what I
want - polygon areas completely inside the box boundary and area, and
not polygons where only the boundary touches the box boundary.
Snapshots:
http://www.kyngchaos.com/wiki/gallery:gis:temp:index
ST_Overlaps() -- only polygons selected where their boundaries touch
the box boundary and any part of the polygon area is inside the box.
I get none that are completely within but not touching are selected.
ST_Intersects() -- all polygons selected where //any// part of the
polygon (boundary and inside) are in or touch //any// part of the box,
though it seems to have missed some from the upper-right neighboring
cells. A lot more than I want.
ST_CoveredBy() -- only polygons where the boundary //and// area are
completely inside only the area of the box and not touching the box
boundary. I don't get the polys touching the box edge.
ST_Within() -- similar to st_coveredby, except that it only seems to
look at the outer boundary of the polygons, and that upper-right
corner polygon is actually an invalid polygon where the "outer"
polygon is a "hole" polygon (not visible here), thus inside and not
touching the box boundary.
Did I miss an obvious function, or is there something that will get
what I want? hmmm, maybe a combination (but would that slow it down a
lot)?
-----
William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
http://www.kyngchaos.com/
[Trillian] What are you supposed to do WITH a maniacally depressed
robot?
[Marvin] You think you have problems? What are you supposed to do if
you ARE a maniacally depressed robot? No, don't try and answer, I'm
50,000 times more intelligent than you and even I don't know the
answer...
- HitchHiker's Guide to the Galaxy
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