ST_LocateBetween with offset drops ZM

[pramsey]

select ST_AsText(ST_LocateBetween('LINESTRING ZM (10 10 10 10, 100 100 20 20)', 12,18 ,0));

[pramsey]

Ah, this is harder than it appears. The order of operations is

• first clip the input line at the appropriate measure points
• second offset the clipped line if necessary

The second step is accomplished by GEOS, which does not preserve Z or M through the offsetting routine (or, frankly, preserve any of the original vertices, the resultant geometry can be entirely net-new).

So this is not an easy fix, it's a very deep improvement in the offset routines of GEOS.