[postgis-users] PostGIS Capabilities
Tyler Mitchell
TMitchell at lignum.com
Thu Feb 19 09:24:33 PST 2004
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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