ST_ForceCurve

What is ST_ForceCurve?

ST_ForceCurve promotes a geometry to its curve-enabled OGC type without changing the vertex data. A LINESTRING becomes a COMPOUNDCURVE containing that line; a POLYGON becomes a CURVEPOLYGON; a MULTILINESTRING becomes a MULTICURVE.

ST_ForceCurve(geometry geom) → geometry

Already-curved geometry is returned unchanged. The function does not detect or reconstruct arcs — use ST_LineToCurve for that.

When would you use ST_ForceCurve?

Use ST_ForceCurve in mixed schemas where some rows contain curves (CIRCULARSTRING, COMPOUNDCURVE) and others are straight but must be cast to the same parent type for uniform column typing — for example, geometry(CompoundCurve, 3857).

It is also helpful in round-trip tests that validate curve-preserving tooling: forcing a straight geometry through the curve type path exposes problems in serializers, ORMs, or client libraries that drop the curve wrapper.

FAQs

Does ST_ForceCurve introduce actual arcs?

No. It only changes the type wrapper — the vertices and their straight-segment interpretation are unchanged. Use ST_LineToCurve to detect and reconstruct arcs.

What if the input is already a curve?

It is returned unchanged (as a new value).

Will it round-trip through text?

Yes — ST_AsText of the forced geometry will show COMPOUNDCURVE(...) or CURVEPOLYGON(...) even when the internals are all straight.

Does it work on MultiPolygons?

Yes. MULTIPOLYGON becomes MULTISURFACE, the OGC curve-enabled counterpart.