[postgis-users] st_split
franco base
frenk.calza at gmail.com
Tue Oct 29 05:03:21 PDT 2013
I use St_intersects only to test the ST_ClosestPoint.
ST_Dwithin(ST_ClosestPoint(line,pt), line,0.001) return true
2013/10/29 Rémi Cura <remi.cura at gmail.com>
> Do you really need st_intersects?
>
> Can you use ST_Dwithin(point, line, your_precision) instead?
>
> Cheers,
>
> Rémi-C
>
>
> 2013/10/29 franco base <frenk.calza at gmail.com>
>
>> Thanks Remi
>> You are very clear now.
>>
>> Meanwhile I make some test and I think there is a bug somewhere.
>> I use the ST_ClosestPoint example documenation
>>
>>
>>
>> SELECT ST_AsText(ST_ClosestPoint(pt,line)) AS cp_pt_line,
>> ST_AsText(ST_ClosestPoint(line,pt)) As cp_line_pt,
>> ST_Contains(line, ST_ClosestPoint(line,pt)), --- f
>> ST_Intersects (line, ST_ClosestPoint(line,pt)), --- f
>> ST_Distance (line, ST_ClosestPoint(line,pt)), ---- 0
>> ST_Line_Locate_Point (line, ST_ClosestPoint(line,pt))
>> --- return value
>>
>> FROM
>> (SELECT 'POINT(100 100)'::geometry As pt,
>> 'LINESTRING (20 80, 98 190, 110 180, 50 75 )'::geometry
>> As line ) As foo
>>
>>
>> give this output:
>>
>>
>> "cp_pt_line";"cp_line_pt";"st_contains";"st_intersects";"st_distance";"st_line_locate_point"
>> "POINT(100 100)";"POINT(73.0769230769231
>> 115.384615384615)";f;f;0;0.828619715102687
>>
>>
>> Something is wrong
>>
>>
>>
>>
>>
>>
>> 2013/10/29 Rémi Cura <remi.cura at gmail.com>
>>
>>> Hey sorry for being unclear.
>>>
>>> I put you a pseudo code and some explanation :
>>>
>>> - first you work with real world data (observation, measure), which
>>> are of a given precision (showing the uncertainty of the measure).
>>> If your data are real world observation ,they may be precise up to
>>> the centimeter, the meter , whatever. So there is no significance of
>>> keeping XXX digits after the comma.
>>> - Second about translating : for your computer manipulating a number
>>> like 650254,2354 is not the same as manipulating a number like 254,2354.
>>> Numbers are represented with double precision, which can be precise
>>> up to* 15 digits *thanks to postgres. Keeping the number of digits
>>> low in your coordinates "free" some precision for computing. You can
>>> translate by any number as long as it reduce the number of digits in the
>>> coordinates.
>>> You can also manually translate like : x := x - 859 ; y:= y - 87426.
>>> - Third : about ST_ClosestPoint : if you point are a result of a
>>> previous computing, they are already of limited precision, thus you have to
>>> compensate this by manually putting the points onto the lines (using
>>> ST_ClosestPoint will give you a new point corresponding to old point
>>> projected onto line).
>>>
>>>
>>>
>>> Here is the pseudo code
>>>
>>> --if your data are of limited precision (always the case ! )
>>> snap to grid (your data precision)
>>>
>>> --before computation
>>> translate everyting (-(min_x+max_x)/2, -(min_y+max_y)/2)
>>>
>>> --computation : do your spatial test
>>>
>>> --if precision issue not solved, use ST_ClosestPoint to project your
>>> point onto lines
>>>
>>> --after computation
>>> translate everyting (+(min_x+max_x)/2, +(min_y+max_y)/2)
>>>
>>> Cheers,
>>>
>>> Rémi-C
>>>
>>>
>>> 2013/10/29 franco base <frenk.calza at gmail.com>
>>>
>>>> Ayway
>>>> St_split and St_snap don't work
>>>>
>>>> SELECT line,
>>>> point,
>>>> st_contains (st_snap (geom_line, geom_point,0.001), geom_point),
>>>> st_geometrytype ((st_dump(ST_split(st_snap (geom_line,
>>>> geom_point,0.001), geom_point))).geom),
>>>> (st_dump(ST_split(st_snap (geom_line, geom_point,0.001),
>>>> geom_point))).geom as splitted_geometry
>>>>
>>>> give
>>>>
>>>> "id";"line";"point";"st_contains";"st_geometrytype";"splitted_geometry"
>>>>
>>>> 1;7646;11764;t;"ST_LineString";"0102000020BB0B000006000000A4703D0A471F37412D211F04AF335341FAEDEBE0491F3741325530C2AE335341BD5296014F1F37418FC2F578AE3353414694F606521F3741D2DEE07BAE3353412D211F74541F37418FC2F578AE3353415713362F611F37410D996234AF335341"
>>>>
>>>> 2;7646;11764;t;"ST_LineString";"0102000020BB0B0000020000005713362F611F37410D996234AF33534123B9FC675020374112143FF6BC335341"
>>>>
>>>> 3;7646;11769;t;"ST_LineString";"0102000020BB0B000006000000A4703D0A471F37412D211F04AF335341FAEDEBE0491F3741325530C2AE335341BD5296014F1F37418FC2F578AE3353414694F606521F3741D2DEE07BAE3353412D211F74541F37418FC2F578AE3353415EF0DD584620374139BF2762BC335341"
>>>>
>>>> 4;7646;11769;t;"ST_LineString";"0102000020BB0B0000020000005EF0DD584620374139BF2762BC33534123B9FC675020374112143FF6BC335341"
>>>>
>>>> 5;7646;11762;t;"ST_LineString";"0102000020BB0B000006000000A4703D0A471F37412D211F04AF335341FAEDEBE0491F3741325530C2AE335341BD5296014F1F37418FC2F578AE3353414694F606521F3741D2DEE07BAE3353412D211F74541F37418FC2F578AE335341A5CBC785841F374156A2A33CB1335341"
>>>>
>>>> 6;7646;11762;t;"ST_LineString";"0102000020BB0B000002000000A5CBC785841F374156A2A33CB133534123B9FC675020374112143FF6BC335341"
>>>>
>>>> St_geometrytype=ST_LineString but in qgis I have point and line.
>>>>
>>>> point splitted geometry (id =2,4,6) = geom_point (starting gometry)
>>>> line splitted geometry (id =1,3,5) = geom_line (starting gometry)
>>>>
>>>>
>>>> 2013/10/29 franco base <frenk.calza at gmail.com>
>>>>
>>>>> Hi.
>>>>> Yes the cause can be that every function has his own "tolerance"
>>>>>
>>>>> SELECT line,geom_line,point,geom_point,
>>>>> ST_ClosestPoint(geom_line,geom_point), ----- return geometry=geom_point
>>>>> ST_distance (geom_line,geom_point), ---- return 0
>>>>> ST_contains(geom_line,geom_point) ---- return false
>>>>>
>>>>>
>>>>> "line";"geom_line";"point";"geom_point";"st_closestpoint";"st_distance";"st_contains"
>>>>>
>>>>> 7646;"0102000020BB0B000006000000A4703D0A471F37412D211F04AF335341FAEDEBE0491F3741325530C2AE335341BD5296014F1F37418FC2F578AE3353414694F606521F3741D2DEE07BAE3353412D211F74541F37418FC2F578AE33534123B9FC675020374112143FF6BC335341";11764;"0101000020BB0B00005713362F611F37410D996234AF335341";"0101000020BB0B00005713362F611F37410D996234AF335341";0;f
>>>>>
>>>>> 7646;"0102000020BB0B000006000000A4703D0A471F37412D211F04AF335341FAEDEBE0491F3741325530C2AE335341BD5296014F1F37418FC2F578AE3353414694F606521F3741D2DEE07BAE3353412D211F74541F37418FC2F578AE33534123B9FC675020374112143FF6BC335341";11769;"0101000020BB0B00005EF0DD584620374139BF2762BC335341";"0101000020BB0B00005EF0DD584620374139BF2762BC335341";0;f
>>>>>
>>>>> 7646;"0102000020BB0B000006000000A4703D0A471F37412D211F04AF335341FAEDEBE0491F3741325530C2AE335341BD5296014F1F37418FC2F578AE3353414694F606521F3741D2DEE07BAE3353412D211F74541F37418FC2F578AE33534123B9FC675020374112143FF6BC335341";11762;"0101000020BB0B0000A5CBC785841F374156A2A33CB1335341";"0101000020BB0B0000A5CBC785841F374156A2A33CB1335341";0;f
>>>>>
>>>>> Remi I don't undesrtand very well your tip to translate date and use
>>>>> St_SnapToGrid
>>>>>
>>>>> I cannot snap (using St_Snap) line to point because I'm working on a
>>>>> road network and I cannot move the line versus point.
>>>>>
>>>>>
>>>>> Thanks
>>>>> fb
>>>>>
>>>>>
>>>>> 2013/10/28 Rémi Cura <remi.cura at gmail.com>
>>>>>
>>>>>> I had the same problem,
>>>>>> all function don't react the same way when hitting precision limit.
>>>>>>
>>>>>> You may want to translate your data to reduce digits, and/or use
>>>>>> ST_SnapToGrid on everything before using ST_ClosestPoint.
>>>>>>
>>>>>> Cheers,
>>>>>> Rémi-C
>>>>>>
>>>>>>
>>>>>> 2013/10/28 Nicolas Ribot <nicolas.ribot at gmail.com>
>>>>>>
>>>>>>> Hmm this is strange:
>>>>>>>
>>>>>>> Finding the closest point (st_closestPoint) or using
>>>>>>> st_lineLocatePoint to project point onto the line does not work
>>>>>>> either
>>>>>>> on the provided dataset.
>>>>>>> Though the st_distance(line, point) returns 0.
>>>>>>>
>>>>>>> Nicolas
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 28 October 2013 18:42, Rémi Cura <remi.cura at gmail.com> wrote:
>>>>>>> > You may want to split not with point but with the projected point
>>>>>>> one line
>>>>>>> > (use http://postgis.refractions.net/docs/ST_ClosestPoint.html)
>>>>>>> > If it is not enough, you may want to translate all your geometries
>>>>>>> to reduce
>>>>>>> > the number of digits in coordinates.
>>>>>>> > Another possibility is to use ST_Snap to snap line to point (won't
>>>>>>> work the
>>>>>>> > other way)
>>>>>>> >
>>>>>>> > Cheers,
>>>>>>> > Rémi-C
>>>>>>> >
>>>>>>> >
>>>>>>> > 2013/10/28 Nicolas Ribot <nicolas.ribot at gmail.com>
>>>>>>> >>
>>>>>>> >> Hi,
>>>>>>> >>
>>>>>>> >> The points are not on the line, probably due to rounding errors.
>>>>>>> >>
>>>>>>> >> st_contains(line, point) returns false.
>>>>>>> >>
>>>>>>> >> Nicolas
>>>>>>> >>
>>>>>>> >> On 28 October 2013 18:07, franco base <frenk.calza at gmail.com>
>>>>>>> wrote:
>>>>>>> >> > Hi.
>>>>>>> >> > I have a set of linestring and point on linestring.
>>>>>>> >> > I want cut the linestring on the point.
>>>>>>> >> > I can have n points for one linestring,
>>>>>>> >> > so I use ST_Split
>>>>>>> >> > (insted of ST_Line_Interpolate_Point and ST_Line_Substring)
>>>>>>> >> > but it doesn't work.
>>>>>>> >> >
>>>>>>> >> > line;geom_line;point;geom_point
>>>>>>> >> >
>>>>>>> >> >
>>>>>>> 7646;"0102000020BB0B000006000000A4703D0A471F37412D211F04AF335341FAEDEBE0491F3741325530C2AE335341BD5296014F1F37418FC2F578AE3353414694F606521F3741D2DEE07BAE3353412D211F74541F37418FC2F578AE33534123B9FC675020374112143FF6BC335341";11764;"0101000020BB0B00005713362F611F37410D996234AF335341"
>>>>>>> >> >
>>>>>>> >> >
>>>>>>> 7646;"0102000020BB0B000006000000A4703D0A471F37412D211F04AF335341FAEDEBE0491F3741325530C2AE335341BD5296014F1F37418FC2F578AE3353414694F606521F3741D2DEE07BAE3353412D211F74541F37418FC2F578AE33534123B9FC675020374112143FF6BC335341";11769;"0101000020BB0B00005EF0DD584620374139BF2762BC335341"
>>>>>>> >> >
>>>>>>> >> >
>>>>>>> 7646;"0102000020BB0B000006000000A4703D0A471F37412D211F04AF335341FAEDEBE0491F3741325530C2AE335341BD5296014F1F37418FC2F578AE3353414694F606521F3741D2DEE07BAE3353412D211F74541F37418FC2F578AE33534123B9FC675020374112143FF6BC335341";11762;"0101000020BB0B0000A5CBC785841F374156A2A33CB1335341"
>>>>>>> >> >
>>>>>>> >> > ST_GeometryType(St_Split(geom_line, geom_point))
>>>>>>> >> > give "ST_GeometryCollection"
>>>>>>> >> >
>>>>>>> >> > but
>>>>>>> >> >
>>>>>>> >> > (ST_Dump(ST_Split(geom_line, geom_point))).geom
>>>>>>> >> >
>>>>>>> >> > return only 3 linestring (one for record) and the geometry is
>>>>>>> egual to
>>>>>>> >> > geom_line
>>>>>>> >> >
>>>>>>> >> >
>>>>>>> >> > thanks.
>>>>>>> >> >
>>>>>>> >> > fb
>>>>>>> >> >
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