[postgis-users] ST_MinkowskiSum

[Stephen Mather]

Hit send too soon...

Hi All,

Digging SFCGAL... .  Quick question-- is ST_MinkowskiSum a 2D calculation
of the Minkowski Sum when non-polyhedral surfaces are fed in?  For example,
I tried this:

WITH pointt AS (

SELECT ST_MakePoint(0,0,0) AS the_geom

),

buffered AS (

SELECT ST_Buffer(the_geom, 30, 20) AS the_geom FROM pointt

),

rotatedOnItsSideX AS (

SELECT ST_RotateX(the_geom, 0.25 * pi()) AS the_geom from buffered

),

minkowski_sum AS (

SELECT ST_MinkowskiSum(x.the_geom, b.the_geom) AS the_geom FROM

rotatedOnItsSideX x, buffered b

)

SELECT ST_AsText(the_geom) from minkowski_sum;


I get:


MULTIPOLYGON(((-60 -7.45012945754965e-14,-59.9075200119938
-2.35377287183542,-59.8150400239877 -4.01814163088313,-59.538170229848
-6.35740271025471,-59.2613004357083 -8.01151008244411,-58.8017478297844
-10.3218370469144,-58.3421952238606 -11.9554849102494, (...)


Thanks,

Best,

Steve




On Sat, Dec 7, 2013 at 5:51 PM, Stephen Mather <stephen at smathermather.com>wrote:

> Hi All,
>
> Digging SFCGAL... .  Quick question-- is ST_MinkowskiSum a 2D calculation
> of the Minkowski Sum when non-polyhedral surfaces are fed in?  For example,
> I tried this:
>
> WITH pointt AS (
>
> SELECT ST_MakePoint(0,0,0) AS the_geom
>
> ),
>
> buffered AS (
>
> SELECT ST_Buffer(the_geom, 30, 20) AS the_geom FROM pointt
>
> ),
>
> rotatedOnItsSideX AS (
>
> SELECT ST_RotateX(the_geom, 0.25 * pi()) AS the_geom from buffered
>
> ),
>
> minkowski_sum AS (
>
> SELECT ST_MinkowskiSum(x.the_geom, b.the_geom) AS the_geom FROM
>
> rotatedOnItsSideX x, buffered b
>
> )
>
> SELECT 1 as gid, ST_AsText(the_geom) from minkowski_sum;
>
>
>
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