I wrote a semplified example:
with this line:
geomfromtext('LINESTRING(15 56,80 12)')
and this substring line:
st_line_substring(geomfromtext('LINESTRING(15 56,80 12)'),0,0.6)
=> LINESTRING(15 56,54 29.6)
if i make the intersection i get only the first point:
st_intersection(
geomfromtext('LINESTRING(15 56,80 12)'),
st_line_substring(geomfromtext('LINESTRING(15 56,80 12)'),0,0.6)
)
=> POINT(15 56)
my expected result should be:
=> LINESTRING(15 56,54 29.6)
because if I take a substring of a line, the intersection with the
original line is the
substring line, correct?
thx for any help on this strange thing
Daniele
On 03. 07. 12 13:35, Daniele Debernardi wrote:
hi,
I have a problem with an intersection with 2 lines that don't return
what I expect:
sample intersection between a line and a substring of the same line:
first line: LINESTRING(675315.7 158956.9,675280 158912.9)
second: st_makeline(geomfromtext('POINT(675315.7 158956.9)'),
ST_Line_Interpolate_Point(geomfromtext('LINESTRING(675315.7
158956.9,675280 158912.9)'),0.6))
select st_astext(st_intersection(
geomfromtext('LINESTRING(675315.7 158956.9,675280 158912.9)'),
st_makeline(geomfromtext('POINT(675315.7 158956.9)'),
ST_Line_Interpolate_Point(geomfromtext('LINESTRING(675315.7
158956.9,675280 158912.9)'),0.6))
));
result: POINT(675315.7 158956.9)
what I expect is that the result of the intersection is not only the
point of start of the 2 lines, but a linestring
starting with that point but ending with the point returned by the
interpolation (expected to be over the line)
I'm doing something wrong with the intersection? there is another way
to get the result I expect?
or is a problem in postgis?
ps: I'm using the POSTGIS 1.5.3 version
thx for help
Daniele
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Cordiali saluti,
ing. Daniele Debernardi
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