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Return the number of points in an ST_LineString or ST_CircularString value. Prior to 1.4 only works with linestrings as the specs state. From 1.4 forward this is an alias for ST_NPoints which returns number of vertexes for not just linestrings. Consider using ST_NPoints instead which is multi-purpose and works with many geometry types.
This method implements the OGC Simple Features Implementation Specification for SQL 1.1.
SELECT ST_NumPoints(ST_GeomFromText('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)')); --result 4