6.2.2.4 Elliptic arc

An elliptic arc is stored in the go_elarc structure. It has the GOT_ELARC type and one of the following subtypes:

• GOST_ELARC_XYR for arcs defined by the center point and radii
• GOST_ELARC_FOCI for arcs defined by the two foci and a point
• GOST_ELARC_3SMALL for the smallest elliptic arcs (in area) which contain the three given points
• GOST_ELARC_3ECC for arcs defined by three points on the perimeter, rotation and eccentricity
• GOST_ELARC_XY1ECC for arcs defined by the center point, a point on the perimeter, rotation and eccentricity

The anchor set differs according to the subtype. Every elliptic arc has a curve hanger, and hangers for start point, end point, and center point. In addition to the subtype, the arc has an important property called “conic”. The available values of the property depend on the subtype. The values for all subtypes are:

• start-entire – a closed arc
• start-dif – an arc defined by the “start” parameter with “dif” defining the arc length

The available values for arcs with at least one point on the perimeter:

• point-entire – a closed arc
• point-dif – an arc starting from the start point with “dif” defining the arc length

The available values for arcs with three points on the perimeter:

• ccw – an arc connecting the three given points counterclockwise
• cw – an arc connecting the three given points clockwise
• smaller – the smaller one of the two arcs connecting the start point and the end point and having the third point on the perimeter of the whole circle/ellipse
• bigger – the larger one (dtto)
• middle – the arc connecting the start point and the end point via the center point
• opposite – the opposite to “middle”