I did something similar a few years back with LINESTRINGs. I had a
large 3D linear dataset that I was constantly fine-tuning and adjusting
the Z component of. Rather than always modifying the stored geometry
(which was a real pain since just rebuilding the index took a couple of
hours), I extracted the Z components out as a double[] into a separate
table that I could update as needed. I wrote a very simple plpgsql
function that merged the 3 ordinate back into the geometry for viewing
purposes, but this allowed me to do a bunch of analysis on the Z array
directly with other simple plpgsql functions, like min/max z values,
min/max slope, std deviation, waterfall detection algorithms, smoothed
elevation algorithms, etc.
Although it's old, the merging function might be of some use to you, it
went something like:
CREATE OR REPLACE FUNCTION adddimension(geometry, double precision[])
RETURNS geometry AS
'SELECT makeline(
makepoint(
x(pointn($1, index)),
y(pointn($1, index)),
$2[index]))
FROM
(select generate_series(1, numpoints($1)) AS index,
$1 as the_geom) foo'
LANGUAGE 'sql' VOLATILE;
Which yields results like:
select asewkt(
adddimension(
'LINESTRING(1 1, 2 2)'::geometry,
ARRAY[3, 4]
)
)
asewkt
-------------------------
LINESTRING(1 1 3,2 2 4)
(1 row)
Cheers,
Kevin
On 4/19/2010 2:19 PM, Chris English wrote:
Hello,
I've been wrestling around with 3D and have gotten my table/geom to x,y,z
so that
SELECT ST_AsEwkt(the_geom) FROM <table>
LIMIT 1;
returns
"MULTIPOLYGON(((611630.148961496 690526.520745486 0,611619.960661661
690507.134957485 0,
611545.79119058 690545.364867903 0,611556.435198162 690565.595798574
0,611630.148961496 690526.520745486 0)))"
In another column are the values I'd like to use for Z, or calculate
Z from.
And then brain death. What sort of statement would I be using to
update the Z part of the XYZ, as a calculated result
from another column.
Any help or suggestions greatly appreciated.
Chris
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
