[postgis-users] Another few questions

[Stephen Woodbridge]

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.
> 

Paul,

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.

-Steve