Re: [postgis-users] Order of linestrings when using st_linemerge

2018-02-12 Thread Komяpa 
Hi,

ST_LineMerge is 2D, you will also have temporal issues when trying to merge
loops.

We've been storing timestamp in Z, but needed ST_Linemerge analog for that.
Here's what we use now:
https://github.com/gojuno/lostgis/blob/master/sql/functions/ST_TimeLineMerge.sql


You can also check if ST_MakeLine suits your needs - in aggregate form it
can consume linestring segments and just stitch them in order, generating
lacking segments as straight lines.

пн, 12 февр. 2018 г. в 11:52, Ben Madin :

> G'day all,
>
> I have an example where I have a large number of multilinestrings
> representing the seaway track  from one port to another. In order to
> interpolate the position of  a vessel (this is historical data) along these
> tracks, we used a combination of st_linemerge and st_interpolate.
>
> The multilinestring respects the direction of travel (from the origin to
> the destination), so we thought this approach would work.
>
> However, to use st_interpolate, we need linestrings, so we used linemerge
> (looks perfect) but the line now goes from the destination to the origin.
> (of course, this is not predictable - sometimes it is in the right order).
>
> Is there any way to 'force' the linestring to have the same ordering as
> the multi-line string? we are using linestringm, can we take advantage of
> the M value?
>
> example:
>
> SELECT
> st_asewkt(st_linemerge(st_geomfromewkt('SRID=4326;MULTILINESTRINGM((115.723248216579
> -32.0454874969596 1,115.356718360803 -31.2649393614626
> 1.47593019400197,114.996206563468 -30.4833681123784
> 1.94793716099846,114.641442213985 -29.70082100447
> 2.41616662431401,114.292166370259 -28.9173431382814
> 2.88076010193012,113.948131063039 -28.1329775961666
> 3.34185510703625,113.609098642971 -27.347765569158
> 3.79958533994624,113.274841167352 -26.5617464753925
> 4.25408087178885,112.945139823841 -25.7749580707562
> 4.70546832037234),(112.945139823841 -25.7749580707562
> 4.70546832037234,112.569944851044 -24.955984154436
> 5.17822970085566,112.199711533849 -24.1360828251298
> 5.64785480680645,111.834198632833 -23.3153001472376
> 6.11447655756696,111.473173947045 -22.493680351942
> 6.57822465026799,111.116413762924 -21.6712659546459
> 7.03922572419879,110.763702333863 -20.8480978652059
> 7.49760351897373,110.414831388289 -20.0242154915183
> 7.95347902680775,110.069599664243 -19.1996568369764
> 8.40697063920594,109.727812468601 -18.3744585922724
> 8.85819428836509,109.389281259168 -17.5486562219864
> 9.30726358357774,109.053823248005 -16.7222840463694
> 9.75428994291997,108.721261024435 -15.8953753186967
> 10.1993827204972,108.391422196296 -15.0679622985443
> 10.6426493295126,108.06413904806 -14.2400763213105
> 11.0841953614157,107.73924821455 -13.411747864288
> 11.524124701379,107.416590369051 -12.5830066095668
> 11.9625396403441,107.096009924666 -11.7538815040321
> 12.3995409838705,106.777354747869 -10.9244008167035
> 12.8352281580124,106.46047588321 -10.0945921936453
> 13.2696993124424,106.145227288244 -9.2644827106659
> 13.7030514210349,105.831465577744 -8.43409892401077
> 14.1353803801144,105.519049776353 -7.60346691924052
> 14.5667811045696,105.207841078825 -6.77261235847855
> 14.997347622028),(105.990650130672 -5.91167003050344
> 14.997347622028,105.599572459125 -6.34228797455069
> 15.2785767014246,105.207841078825 -6.77261235847855
> 15.5600407259128),(106.663050248418 -5.99905605734687
> 15.5600407259128,105.990650130672 -5.91167003050344
> 15.8868531270388),(106.881437549142 -6.08393762734487
> 15.8868531270388,106.709016406789 -6.01184678072196
> 15.9769961743295),(106.709016406789 -6.01184678072196
> 15.9769961743295,106.663050248418 -5.99905605734687 16))')));
>
>
> cheers
>
> Ben
>
>
>
>
> --
>
> Ben Madin
> BVMS PhD
>
>
>
> m : +61 448 887 220 <+61%20448%20887%20220>
>
> e : b...@ausvet.com.au
>
> 5 Shuffrey Street, Fremantle
> Western Australia
>
> on the web: www.ausvet.com.au
>
>
> This transmission is for the intended addressee only and is confidential
> information. If you have received this transmission in error, please delete
> it and notify the sender. The contents of this email are the opinion of the
> writer only and are not endorsed by Ausvet unless expressly stated
> otherwise. Although Ausvet uses virus scanning software we do not accept
> liability for viruses or similar in any attachments.
> ___
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[postgis-users] Order of linestrings when using st_linemerge

2018-02-12 Thread Ben Madin 
G'day all,

I have an example where I have a large number of multilinestrings
representing the seaway track  from one port to another. In order to
interpolate the position of  a vessel (this is historical data) along these
tracks, we used a combination of st_linemerge and st_interpolate.

The multilinestring respects the direction of travel (from the origin to
the destination), so we thought this approach would work.

However, to use st_interpolate, we need linestrings, so we used linemerge
(looks perfect) but the line now goes from the destination to the origin.
(of course, this is not predictable - sometimes it is in the right order).

Is there any way to 'force' the linestring to have the same ordering as the
multi-line string? we are using linestringm, can we take advantage of the M
value?

example:

SELECT
st_asewkt(st_linemerge(st_geomfromewkt('SRID=4326;MULTILINESTRINGM((115.723248216579
-32.0454874969596 1,115.356718360803 -31.2649393614626
1.47593019400197,114.996206563468 -30.4833681123784
1.94793716099846,114.641442213985 -29.70082100447
2.41616662431401,114.292166370259 -28.9173431382814
2.88076010193012,113.948131063039 -28.1329775961666
3.34185510703625,113.609098642971 -27.347765569158
3.79958533994624,113.274841167352 -26.5617464753925
4.25408087178885,112.945139823841 -25.7749580707562
4.70546832037234),(112.945139823841 -25.7749580707562
4.70546832037234,112.569944851044 -24.955984154436
5.17822970085566,112.199711533849 -24.1360828251298
5.64785480680645,111.834198632833 -23.3153001472376
6.11447655756696,111.473173947045 -22.493680351942
6.57822465026799,111.116413762924 -21.6712659546459
7.03922572419879,110.763702333863 -20.8480978652059
7.49760351897373,110.414831388289 -20.0242154915183
7.95347902680775,110.069599664243 -19.1996568369764
8.40697063920594,109.727812468601 -18.3744585922724
8.85819428836509,109.389281259168 -17.5486562219864
9.30726358357774,109.053823248005 -16.7222840463694
9.75428994291997,108.721261024435 -15.8953753186967
10.1993827204972,108.391422196296 -15.0679622985443
10.6426493295126,108.06413904806 -14.2400763213105
11.0841953614157,107.73924821455 -13.411747864288
11.524124701379,107.416590369051 -12.5830066095668
11.9625396403441,107.096009924666 -11.7538815040321
12.3995409838705,106.777354747869 -10.9244008167035
12.8352281580124,106.46047588321 -10.0945921936453
13.2696993124424,106.145227288244 -9.2644827106659
13.7030514210349,105.831465577744 -8.43409892401077
14.1353803801144,105.519049776353 -7.60346691924052
14.5667811045696,105.207841078825 -6.77261235847855
14.997347622028),(105.990650130672 -5.91167003050344
14.997347622028,105.599572459125 -6.34228797455069
15.2785767014246,105.207841078825 -6.77261235847855
15.5600407259128),(106.663050248418 -5.99905605734687
15.5600407259128,105.990650130672 -5.91167003050344
15.8868531270388),(106.881437549142 -6.08393762734487
15.8868531270388,106.709016406789 -6.01184678072196
15.9769961743295),(106.709016406789 -6.01184678072196
15.9769961743295,106.663050248418 -5.99905605734687 16))')));


cheers

Ben




-- 

Ben Madin
BVMS PhD



m : +61 448 887 220

e : b...@ausvet.com.au

5 Shuffrey Street, Fremantle
Western Australia

on the web: www.ausvet.com.au


This transmission is for the intended addressee only and is confidential
information. If you have received this transmission in error, please delete
it and notify the sender. The contents of this email are the opinion of the
writer only and are not endorsed by Ausvet unless expressly stated
otherwise. Although Ausvet uses virus scanning software we do not accept
liability for viruses or similar in any attachments.
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