[postgis-users] Another few questions
woodbri at swoodbridge.com
Sun Mar 30 13:21:48 PDT 2008
Paul Tomblin wrote:
> Bruce Rindahl wrote:
>>> 3. Is there any way to get the corners of a polygon or its bounding
>>> box out
>>> as separate points?
>> See the documentation on xmin, xmax, ymin, ymax
> What documentation? In http://postgis.refractions.net/docs/ch06.html,
> all I can find is "ST_xmin(box3d)". But experimentation shows I can
> call 'xmin()' with a geometry, and 'st_xmin()' doesn't exist.
> This is what I find so frustrating about the PostGIS documentation.
> There are all these functions documented as "ST_*" but it turns out that
> in order to use some of them, you actually have to leave off the "ST_"
> part. This function is defined as requiring a box3d, but nothing I can
> find in the docs actually comes out and says that if you have a method
> that takes a box3d, you can call it with a geometry and it will use the
> bounding box (ok, it does come out and say that for the && operator, but
> it doesn't say it's true in general).
> I'm really trying to read the manual before asking dumb questions, but
> the manual is horrible.
Just FYI, all the ST_* functions are very new and they automatic try to
use spatial index where the older ones do not and you had to explicitly
specify a clause with the && operator.
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