My question is about the differences between st_length() and st_m() in postgis.

The reason I ask this is because in a MultiLineString I can´t calculate st_m(), but I can st_length().

1 Answer 1


ST_M() returns the M coordinate of the point so is undefined on a MultiLineString. ST_Length() returns the length of the line so is well defined for your MultiLineString (though would return 0 if you use a polygon).

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