[postgis-users] PostGIS Capabilities

[Tyler Mitchell]

That's a lot of affirmatives Paul - Now I remember why I'm so pumped about 
PostGIS!

postgis-users-bounces at postgis.refractions.net wrote on 02/19/2004 07:15:48 
AM:

> 
> On Thursday, February 19, 2004, at 02:03 AM, Chris Haste wrote:
> 
> > Given an irregular closed polygon can we perform SQL statements along 
> > the lines of "give me all the points that reside within the polygon?
> 
> SELECT POINTS FROM MYTABLE WHERE 
> CONTAINS(GEOMETRYFROMTEXT('POLYGON(..)', SRID), POINTS)
> 
> 
> >  Given the same polygon can we obtain all the lines that intersect the 

> > polygon?
> 
> SELECT LINES FROM MYTABLE WHERE NOT 
> DISJOINT(GEOMETRYFROMTEXT('POLYGON(..)', SRID), LINES)
> 
> 
> >  For the above are the coordinates of the intersection points 
> > calculated and obtainable?
> 
> SELECT INTERSECTION(LINES, GEOMETRYFROMTEXT('POLYGON(..)',SRID)) FROM 
> MYTABLE WHERE NOT DISJOINT(GEOMETRYFROMTEXT('POLYGON(..)', SRID), LINES)
> 
> 
> >  Can we obtain all the points within a certain radius of a specified 
> > points?
> 
> SELECT * FROM MYTABLE WHERE 
> DISTANCE(POINTS,GEOMETRYFROMTEXT('POINT(..)',SRID)) > RADIUS
> 
> > Can we obtain all the lines that reside entirely (without intersecting 

> > the boundary) within a circle or an ellipse?
> 
> If you construct the circle or ellipse into a polygon that approximates 
> the shape, you can use the WITHIN() or CONTAINS() functions for a 
> strict test of containment.
> 
> > Is it possible to specify the segments of a polygon as being either a 
> > straight line, a rhumb line or a great circle? This is necessary to 
> > avoid problems to do with the curvature of the earth.
> 
> No. You can calculate length_spheroid() directly on the spheroid, but 
> that is the only geodetic function we have so far.
> 
> >  
>       Paul Ramsey
>       Refractions Research
>       Email: pramsey at refractions.net
>       Phone: (250) 885-0632
> 
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