PostGIS make buffer on LINESTRING Z to have a POLYGON Z - postgresql
I have several LINESTRING Z geometies in PostgreSQL and they look like
LINESTRING Z (1 2 1,1 1 4)
I want to make a buffer around this linestring so that i can have a POLYGON Z geometry for further export to dxf.
I tried this
select st_astext(st_buffer('LINESTRING Z (1 2 1,1 1 4)'::geometry, 2)) as geom;
and it gives me
POLYGON((3 1,2.96157056080646 0.609819355967741,2.84775906502257 0.23463313526
9818,2.66293922460509 -0.111140466039206,2.41421356237309 -0.414213562373096,2.
1111404660392 -0.662939224605091,1.76536686473018 -0.847759065022574,1.39018064
403226 -0.961570560806461,1 -1,0.609819355967745 -0.961570560806461,0.234633135
269822 -0.847759065022574,-0.111140466039202 -0.662939224605092,-0.414213562373
094 -0.414213562373096,-0.662939224605089 -0.111140466039207,-0.847759065022572
0.234633135269818,-0.96157056080646 0.609819355967739,-1 1,-1 2,-0.96157056080
646 2.39018064403226,-0.847759065022572 2.76536686473018,-0.662939224605089 3.1
1114046603921,-0.414213562373094 3.4142135623731,-0.111140466039203 3.662939224
60509,0.234633135269821 3.84775906502257,0.609819355967744 3.96157056080646,1 4
,1.39018064403226 3.96157056080646,1.76536686473018 3.84775906502257,2.11114046
60392 3.66293922460509,2.41421356237309 3.4142135623731,2.66293922460509 3.1111
4046603921,2.84775906502257 2.76536686473018,2.96157056080646 2.39018064403226,
3 2,3 1)) (1 row)
which is in 2D POLYGON not POLYGON Z
How can I make it 3D?
I'm not totally sure what you want to achieve, but did you take a look at ST_Force3D?
SELECT
ST_AsText(
ST_Force3D(
ST_Buffer('LINESTRING Z (1 2 1,1 1 4)'::GEOMETRY, 2)));
It will return a POLYGON Z geometry:
POLYGON Z ((3 1 0,2.96157056080646 0.609819355967741 0,2.84775906502257 0.234633135269818 0,2.66293922460509 -0.111140466039206 0,2.41421356237309 -0.414213562373096 0,2.1111404660392 -0.662939224605091 0,1.76536686473018 -0.847759065022574 0,1.39018064403226 -0.961570560806461 0,1 -1 0,0.609819355967745 -0.961570560806461 0,0.234633135269822 -0.847759065022574 0,-0.111140466039202 -0.662939224605092 0,-0.414213562373094 -0.414213562373096 0,-0.662939224605089 -0.111140466039207 0,-0.847759065022572 0.234633135269818 0,-0.96157056080646 0.609819355967739 0,-1 1 0,-1 2 0,-0.96157056080646 2.39018064403226 0,-0.847759065022572 2.76536686473018 0,-0.662939224605089 3.11114046603921 0,-0.414213562373094 3.4142135623731 0,-0.111140466039203 3.66293922460509 0,0.234633135269821 3.84775906502257 0,0.609819355967744 3.96157056080646 0,1 4 0,1.39018064403226 3.96157056080646 0,1.76536686473018 3.84775906502257 0,2.1111404660392 3.66293922460509 0,2.41421356237309 3.4142135623731 0,2.66293922460509 3.11114046603921 0,2.84775906502257 2.76536686473018 0,2.96157056080646 2.39018064403226 0,3 2 0,3 1 0))
The function ST_Buffer discards the Z dimension, as stated in the documentation:
... This function ignores the third dimension (z) and will always give a
2-d buffer even when presented with a 3d-geometry.
EDIT:
This query sort of creates a buffer with the average Z value of a given LINESTRING Z.
WITH j AS (
SELECT
ST_DumpPoints(
ST_Buffer('LINESTRING Z (1 2 1,1 1 4)'::GEOMETRY, 2)
) AS pt,
(SELECT AVG(z) AS avg_z
FROM (SELECT ST_Z((ST_DumpPoints('LINESTRING Z (1 2 1,1 1 4)'::GEOMETRY)).geom) AS z) AS z) AS lsz
)
SELECT ST_AsText(
ST_MakePolygon(ST_MakeLine(ST_MakePoint(ST_X((pt).geom),ST_Y((pt).geom),lsz))))
FROM j
GROUP BY lsz;
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
POLYGON Z ((3 1 2.5,2.96157056080646 0.609819355967741 2.5,2.84775906502257 0.234633135269818 2.5,2.66293922460509 -0.111140466039206 2.5,2.41421356237309 -0.414213562373096 2.5,2.1111404660392 -0.662939224605091 2.5,1.76536686473018 -0.847759065022574 2.5,1.39018064403226 -0.961570560806461 2.5,1 -1 2.5,0.609819355967745 -0.961570560806461 2.5,0.234633135269822 -0.847759065022574 2.5,-0.111140466039202 -0.662939224605092 2.5,-0.414213562373094 -0.414213562373096 2.5,-0.662939224605089 -0.111140466039207 2.5,-0.847759065022572 0.234633135269818 2.5,-0.96157056080646 0.609819355967739 2.5,-1 1 2.5,-1 2 2.5,-0.96157056080646 2.39018064403226 2.5,-0.847759065022572 2.76536686473018 2.5,-0.662939224605089 3.11114046603921 2.5,-0.414213562373094 3.4142135623731 2.5,-0.111140466039203 3.66293922460509 2.5,0.234633135269821 3.84775906502257 2.5,0.609819355967744 3.96157056080646 2.5,1 4 2.5,1.39018064403226 3.96157056080646 2.5,1.76536686473018 3.84775906502257 2.5,2.1111404660392 3.66293922460509 2.5,2.41421356237309 3.4142135623731 2.5,2.66293922460509 3.11114046603921 2.5,2.84775906502257 2.76536686473018 2.5,2.96157056080646 2.39018064403226 2.5,3 2 2.5,3 1 2.5))
(1 row)
Related
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How does this kbd function work?
Would someone please explain the below function? How does the kdb utilize x here?
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svcs:`TEST:1`TEST:2
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TEST:1 select count sym from trades
TEST:1 select sum size from trades
TEST:2 select count sym from trades
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q){show enlist "x 0 is ",string x 0;show enlist "x 1 is ",string x 1;show raze "
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"x 1 is select sum size from trades"
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"x 0 1 is TEST:2 & select count sym from trades"
"x 0 is TEST:2"
"x 1 is select sum size from trades"
"x 0 1 is TEST:2 & select sum size from trades"
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q)x:(`TEST:1;`$"select count sym from trades")
q)x 0
`TEST:1
q)x 1
`select count sym from trades
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I have a set of collinear line segments (may be mutually disjoint, contained, or overlapping). I want to make a new set of line segments where the segments are disjoint or touching (not overlapping), and each line segment has a count of the original line segments that cover it. For example, suppose the original set is (drawn non-collinearly for illustration): A----------------------B C---------------------------D E-----F G-------------H I-------J the desired new set would be: A-------C---E-----F-----B-----------D G-------------H-------J 1 2 3 2 1 1 1 (only the point coordinates matter, the new set does not share point objects with the old set) How can I achieve this with PostGIS? Related question: suppose I start with a table of line segments, not all collinear, how do I write the entire query that groups the collinear segments together and then applies the solution to my first question? Thanks for any help!
Setup (for later queries):
create table lines (
id serial primary key,
label text not null,
line_data geometry(linestring) not null
);
insert into lines(label, line_data)
values ('A-B', ST_MakeLine(ST_MakePoint(-3, -6), ST_MakePoint( 1, 2))),
('D-C', ST_MakeLine(ST_MakePoint( 2, 4), ST_MakePoint(-2, -4))),
('E-F', ST_MakeLine(ST_MakePoint(-1, -2), ST_MakePoint( 0, 0))),
('G-H', ST_MakeLine(ST_MakePoint( 3, 6), ST_MakePoint( 4, 8))),
('I-J', ST_MakeLine(ST_MakePoint( 4, 8), ST_MakePoint( 5, 10))),
('P-L', ST_MakeLine(ST_MakePoint( 1, 0), ST_MakePoint( 2, 2))),
('X-Y', ST_MakeLine(ST_MakePoint( 2, 2), ST_MakePoint( 0, 4)));
Notes:
I purposely switched your D and C points to demonstrate a need for vector negation
The P-L line is parallel with your example lines (but not collinear)
The X-Y line has nothing to do with the others
the solutions below obviously won't work, when you have linestrings that have more than 2 points and those are not on the same line (so when a single linestring is not straight).
The ST_Union aggregate function can split your collinear linestrings. You'll just need to calculate how many lines are containing those.
However, grouping by collinearity is not that simple. I did not find any out-of-the-box solution for this, but you can calculate it (this will not calculate counts yet):
select string_agg(label, ','), ST_AsText(ST_Multi(ST_Union(line_data)))
from lines
group by (
select case
when ST_SRID(s) <> ST_SRID(e) then row(ST_SRID(s), s, null)
when ST_X(s) = ST_X(e) then row(ST_SRID(s), ST_SetSRID(ST_MakePoint(ST_X(s), 1.0), ST_SRID(s)), null)
when ST_Y(s) = ST_Y(e) then row(ST_SRID(s), ST_SetSRID(ST_MakePoint(1.0, ST_Y(e)), ST_SRID(s)), null)
else (
select row(
ST_SRID(s),
(select case
when ST_Y(rv) < 0
then ST_SetSRID(ST_MakePoint(-ST_X(rv), -ST_Y(rv)), ST_SRID(s))
else rv
end), -- normalized vector (negated when necessary, but same for all parallel lines)
(ST_X(e) * ST_Y(s) - ST_X(s) * ST_Y(e)) / (ST_X(e) - ST_X(s)) -- solution of the linear equaltion, where x=0
)
from coalesce(1.0 / nullif(ST_Distance(s, e), 0), 0) dmi, -- distance's multiplicative inverse
ST_TransScale(e, -ST_X(s), -ST_Y(s), dmi, dmi) rv -- raw vector (translated and scaled)
)
end
from ST_StartPoint(line_data) s,
ST_EndPoint(line_data) e
)
will produce:
X-Y | MULTILINESTRING((2 2,0 4))
P-L | MULTILINESTRING((1 0,2 2))
E-F,A-B,I-J,G-H,D-C | MULTILINESTRING((-3 -6,-2 -4),(-2 -4,-1 -2),(-1 -2,0 0),(0 0,1 2),(2 4,1 2),(3 6,4 8),(4 8,5 10))
To calculate counts, JOIN your original data again, where the splitted lines are contained by (ST_Contains) your original lines:
select ST_AsText(splitted_line), count(line_data)
from (select ST_Multi(ST_Union(line_data)) ml
from lines
group by (
select case
when ST_SRID(s) <> ST_SRID(e) then row(ST_SRID(s), s, null)
when ST_X(s) = ST_X(e) then row(ST_SRID(s), ST_SetSRID(ST_MakePoint(ST_X(s), 1.0), ST_SRID(s)), null)
when ST_Y(s) = ST_Y(e) then row(ST_SRID(s), ST_SetSRID(ST_MakePoint(1.0, ST_Y(e)), ST_SRID(s)), null)
else (
select row(
ST_SRID(s),
(select case
when ST_Y(rv) < 0
then ST_SetSRID(ST_MakePoint(-ST_X(rv), -ST_Y(rv)), ST_SRID(s))
else rv
end), -- normalized vector (negated when necessary, but same for all parallel lines)
(ST_X(e) * ST_Y(s) - ST_X(s) * ST_Y(e)) / (ST_X(e) - ST_X(s)) -- solution of the linear equaltion, where x=0
)
from coalesce(1.0 / nullif(ST_Distance(s, e), 0), 0) dmi, -- distance's multiplicative inverse
ST_TransScale(e, -ST_X(s), -ST_Y(s), dmi, dmi) rv -- raw vector (translated and scaled)
)
end
from ST_StartPoint(line_data) s,
ST_EndPoint(line_data) e)) al,
generate_series(1, ST_NumGeometries(ml)) i,
ST_GeometryN(ml, i) splitted_line
left join lines on ST_Contains(line_data, splitted_line)
group by splitted_line
will return:
LINESTRING(-3 -6,-2 -4) | 1
LINESTRING(-2 -4,-1 -2) | 2
LINESTRING(-1 -2,0 0) | 3
LINESTRING(0 0,1 2) | 2
LINESTRING(2 2,0 4) | 1
LINESTRING(1 0,2 2) | 1
LINESTRING(2 4,1 2) | 1
LINESTRING(3 6,4 8) | 1
LINESTRING(4 8,5 10) | 1
Crystal Reports Cross-tab with mix of Sum, Percentages and Computed values
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