1

let's assume a Linestring(Z)M holding a timestamp as measure variable with each point. Is there a way to easily query "on the relation of those timestamps between the points". For example to find segments where duration between two timestamps are larger than x minutes.

I am aware of the ST_LocateBetween function, where I could filter an M-geometry for a certain specified range. But that is more an absolute function and I am more looking at relative filters.

  • It is possible to do unspeakable things with generate_series and ST_PointN, or with ST_Dump, but I, too, would like to know if there's anything better... – Ture Pålsson Nov 5 '19 at 7:58
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I think you can dump individual vertices as geoms using st_dumppoints, compute difference between consecutive rows M values using lag window function and then query that for the required difference. Something like this:

select * from 
(select 
    st_m(geom) - lag(st_m(geom)) over () diff, 
    path 
from ST_DumpPoints(ST_GeomFromText('LINESTRING M (0 0 0, 10 0 20, 12 0 40, 20 0 50, 21 0 70)'))) p
where diff > 10;

which gives you this:

diff|path|
----|----|
  20|{2} |
  20|{3} |
  20|{5} |

Of course, you have to modify over() statement to accommodate your requirements - for example, partition by line ID to compute diff only within one line.

  • Works perfect! Thanks! – ASI Nov 5 '19 at 10:38

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