> How to generate source and target values? The simplest method: Use the pgrouting ready made functions / tools - https://docs.pgrouting.org/latest/en/topology-functions.html - https://docs.pgrouting.org/latest/en/pgr_createTopology.html * SELECT pgr_createTopology('edge_table', 0.001, 'id', 'the_geom');* There is a nice Pgrouting tutorial: https://workshop.pgrouting.org/2.7/en/index.html and they have a chat: https://gitter.im/pgRouting/pgrouting ( see more about support: https://pgrouting.org/support.html )
> Can I understand that source means startpoint of a line, and target means an endpoint of a line? it is a "Graph"; so you have to split the lines into "edges" https://en.wikipedia.org/wiki/Graph_theory#Graph regards, Imre Shaozhong SHI <[email protected]> ezt írta (időpont: 2022. máj. 8., V, 2:37): > > > On Fri, 22 Apr 2022 at 22:14, Imre Samu <[email protected]> wrote: > >> > as St_intersects or recursive query used, >> >> The other alternative ( ~ less efficient ) is using a “noded” network >> table ( "edge_table" ) >> in the recursive query. ( and don't forget to add indexes to the >> "source" and "target" columns ) >> >> WITH RECURSIVE walk_network(id, source, target, targetPoint) AS >> (SELECT et.id,et.source,et.target,ST_EndPoint(the_geom) as targetPoint >> FROM edge_table et WHERE et.id = *12* >> UNION ALL >> SELECT e.id, e.source, e.target ,ST_EndPoint(the_geom) as targetPoint >> FROM edge_table e >> , walk_network w >> WHERE w.target = e.source >> ) >> SELECT ST_AsText(ST_MakeLine(targetPoint)) >> FROM walk_network >> ; >> +---------------------------------+ >> | st_astext | >> +---------------------------------+ >> | LINESTRING(4 2,3 2,2 1,1 1,0 0) | >> +---------------------------------+ >> (1 row) >> >> regards, >> Imre >> >> > How to generate source and target values? > > Regards, > > David > > > >> Imre Samu <[email protected]> ezt írta (időpont: 2022. ápr. 22., P, >> 16:39): >> >>> > With a large data set, >>> >>> :-) >>> please give more detail: >>> - How large? >>> - and what is your real "business problem"? what type of network? >>> >>> >>> > I tried to use this >>> http://blog.cleverelephant.ca/2010/07/network-walking-in-postgis.html in >>> the PostGIS. >>> >>> As I see this is a directed "network graph", and I will try using the >>> pgRouting tool - for a large graph! >>> *( "pgRouting extends the PostGIS/PostgreSQL geospatial database to >>> provide geospatial routing and other network analysis functionality." )* >>> The pgRouting project did not exist in 2010/07 when this blogpost was >>> written! >>> >>> [image: image.png] >>> >>> so I have adapted the example network ( from the original blogpost ) >>> to pgRouting and this is my sample result >>> >>> ---------- ALL "downstream path" from "all deadends" sorted by >>> descending cost --------- >>> >>> +------------+-----------+---------+-------------------------------------+--------------+ >>> | route_cost | start_vid | end_vid | the_geom_text >>> | edge_ids | >>> >>> +------------+-----------+---------+-------------------------------------+--------------+ >>> | 6.24 | 3044 | 3000 | LINESTRING(4 4,3 4,2 3,1 2,1 1,0 0) >>> | {13,9,6,3,1} | >>> | 5.83 | 3043 | 3000 | *LINESTRING(4 3,4 2,3 2,2 1,1 1,0 >>> 0) | {12,8,5,2,1} |* >>> | 4.83 | 3024 | 3000 | LINESTRING(2 4,2 3,1 2,1 1,0 0) >>> | {10,6,3,1} | >>> | 4.41 | 3014 | 3000 | LINESTRING(1 4,1 3,1 2,1 1,0 0) >>> | {11,7,3,1} | >>> | 3.41 | 3031 | 3000 | LINESTRING(3 1,2 1,1 1,0 0) >>> | {4,2,1} | >>> >>> +------------+-----------+---------+-------------------------------------+--------------+ >>> and the second line is same as in the blogpost ( *"Downstream(12)" *example) >>> , >>> just with an extra "deadends" points ; the edges :* {12,8,5,2,1} * >>> >>> start_vid : starting node/vertex id ( "deadends" in this example ) >>> end_vid : ending node/vertex id constant 3000 (0,0) >>> node/vertex id = 3000 + X*10+Y coordinate // ( 2,1 ) --> 3021 ; >>> (0,0) --> 3000 >>> >>> >>> > Whenever geospatial functions such as St_intersects or recursive query >>> used, >>> >>> IMHO: A good scalable data model is extremely important. >>> pgRouting has 2 important (separated) steps. >>> - creating a routing topology - route optimized database ( with "start" >>> - and "end" node/vertex ) >>> - fast routing/graph/"network-walking" functions - without the >>> geometry ( using Boost Graph c++ library ) >>> ( in this example I have used >>> https://docs.pgrouting.org/3.3/en/pgr_dijkstra.html ) >>> >>> >>> and this is my adapted "routing" topology edge table : >>> >>> DROP TABLE IF EXISTS edge_table CASCADE; >>> CREATE TABLE edge_table ( >>> id bigint primary key, >>> source bigint, >>> target bigint, >>> cost float, >>> reverse_cost float, >>> the_geom geometry >>> ); >>> -- network example from >>> -- >>> http://blog.cleverelephant.ca/2010/07/network-walking-in-postgis.html >>> INSERT INTO edge_table VALUES( 1, 3011, 3000, 1, -1, 'LINESTRING(1 1, 0 >>> 0)'); >>> INSERT INTO edge_table VALUES( 2, 3021, 3011, 1, -1, 'LINESTRING(2 1, 1 >>> 1)'); >>> INSERT INTO edge_table VALUES( 3, 3012, 3011, 1, -1, 'LINESTRING(1 2, 1 >>> 1)'); >>> INSERT INTO edge_table VALUES( 4, 3031, 3021, 1, -1, 'LINESTRING(3 1, 2 >>> 1)'); >>> INSERT INTO edge_table VALUES( 5, 3032, 3021, 1, -1, 'LINESTRING(3 2, 2 >>> 1)'); >>> INSERT INTO edge_table VALUES( 6, 3023, 3012, 1, -1, 'LINESTRING(2 3, 1 >>> 2)'); >>> INSERT INTO edge_table VALUES( 7, 3013, 3012, 1, -1, 'LINESTRING(1 3, 1 >>> 2)'); >>> INSERT INTO edge_table VALUES( 8, 3042, 3032, 1, -1, 'LINESTRING(4 2, 3 >>> 2)'); >>> INSERT INTO edge_table VALUES( 9, 3034, 3023, 1, -1, 'LINESTRING(3 4, 2 >>> 3)'); >>> INSERT INTO edge_table VALUES(10, 3024, 3023, 1, -1, 'LINESTRING(2 4, 2 >>> 3)'); >>> INSERT INTO edge_table VALUES(11, 3014, 3013, 1, -1, 'LINESTRING(1 4, 1 >>> 3)'); >>> INSERT INTO edge_table VALUES(12, 3043, 3042, 1, -1, 'LINESTRING(4 3, 4 >>> 2)'); >>> INSERT INTO edge_table VALUES(13, 3044, 3034, 1, -1, 'LINESTRING(4 4, 3 >>> 4)'); >>> >>> full example code - with data&code: >>> https://gist.github.com/ImreSamu/efda6093b67391a0edafff39d8056cb5 >>> >>> if you are interested in more examples.. check the pgRouting tutorial >>> for example: *"Pre-processing waterways data"* >>> >>> https://workshop.pgrouting.org/2.7/en/un_sdg/sdg11-cities.html#pre-processing-waterways-data >>> >>> regards, >>> Imre >>> >>> >>> Shaozhong SHI <[email protected]> ezt írta (időpont: 2022. ápr. >>> 22., P, 1:22): >>> >>>> Whenever geospatial functions such as St_intersects or recursive query >>>> used, the PostGIS appears to spawn away to many child queries and just >>>> obliterate the CPU. Nothing finishes. >>>> >>>> That forced me to try out to do the some tasks on the FME server. >>>> >>>> I tried to use this http://blog.cleverelephant.ca/2010/07/network >>>> -walking-in-postgis.html in the PostGIS. >>>> >>>> I tried to linecombiner in FME. LineCombiner | FME (safe.com) >>>> <https://www.safe.com/transformers/line-combiner/>. >>>> >>>> With a large data set, the running of processors were monitored. It >>>> was estimated the PostGIS one would take 16 days to complete. >>>> >>>> But, it only took a few minute to do the same thing in FME. >>>> >>>> This suggests that something is not right with the PostGIS Server. >>>> >>>> Have anyone got experience with configuration and improving perfomance >>>> of PostGIS Server? >>>> >>>> Regards, >>>> >>>> David >>>> _______________________________________________ >>>> postgis-users mailing list >>>> [email protected] >>>> https://lists.osgeo.org/mailman/listinfo/postgis-users >>>> >>> _______________________________________________ >> postgis-users mailing list >> [email protected] >> https://lists.osgeo.org/mailman/listinfo/postgis-users >> > _______________________________________________ > postgis-users mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/postgis-users >
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