Working with curves in PostGIS

PostGIS included curved geometry data types in version 1.4, but the functions to operate on curves was limited, and required the curve object to be converted into a linearized approximation, using a function such as ST_CurveToLine. In PostGIS 2.0 this will change as the approach is to look at the circle the arc is inscribed on.

In 2.0 arcs are defined using a start point, mid point and end point implying a circle. By calculating the center of the circle it is possible it is possible to determine that a successive point, which occurs the same distance from that center point as the arc points, forms part of the arc.
Read more at Getting Curvey.