• ST_Curve type

• ST_CircularString constructor

• ST_NumPoints method for type ST_CircularString
• ST_PointN method for type ST_CircularString
• All methods of ST_Curve type can also be called on a ST_CircularString type.
• All methods of ST_Geometry type can also be called on a ST_CircularString type.

The ST_CircularString type is a subtype of ST_Curve that uses circular line segments between control points. The first three points define an arc as follows. The first point is the start point of the arc. The second point is any point on the arc other than the start and end point. The third point is the end point of the arc. Subsequent segments are defined by two points only (intermediate and end point). The start point is taken to be the end point of the preceding segment.

A circularstring can be a complete circle with three points if the start and end points are coincident. In this case, the intermediate point is the midpoint of the segment.

If the start, intermediate and end points are collinear, the arc segment is a straight line segment between the start and end point.

A circularstring with exactly three points is a circular arc. A circular ring is a circularstring that is both closed and simple.

Circularstrings are not allowed in round-Earth spatial reference systems. For example, attempting to create one for SRID 4326 returns an error.