More About Curve Types

The ways in which the various types of Curve are specified are as follows:

CURTYP = LINE

Specifies a straight line between the adjacent POINSPs. This is the default if curved geometry is not defined between two POINSP elements.

CURTYP = RADI

Specifies a single circular arc between adjacent POINSP elements. The arc is defined by the RADI (radius) and CPOS (conditioning point) attributes. The conditioning point and the preceding and following points define the plane of the arc. The choice of minor or major arc is governed by the arc which approaches closest to the conditioning point. If RADS = false, the specified radius is ignored and the minimum radius is calculated such that the curve is a semicircle between the adjacent POINSPs.

CURTYP = THRU

Specifies a single circular arc. The arc is defined by the POS attribute, which is interpreted as a through-point on the curve. The through-point and the preceding and following points define the plane of the arc.

CURTYP = BULG

Specifies a single circular arc. The arc is defined by the Bulge Factor (BULG) and Conditioning Point (CPOS) attributes. The conditioning point and the preceding and following points define the plane of the arc. The choice of minor or major arc is governed by the size of the bulge factor. The sign of the bulge factor determines whether the arc curves towards the conditioning point (positive bulge factor) or away from the conditioning point (negative bulge factor).

CURTYP = FILL

Specifies a combination of an arc and up to two straights. The curve is defined by the Radius (RADI) and POS attributes, where the POS setting is interpreted as the pole point of the arc (the intersection of the two end tangents). The pole point and the preceding and following points define the plane of the arc. If RADS = false, the specified radius is ignored and the maximum radius that will fit into the pole is calculated; an endpoint triangle makes sure that the fillet terminates on at least one of the end points.

CURTYP = CENT

Specifies a combination of an arc and up to two straights. The curve is defined by the Radius (RADI), Conditioning Point (CPOS) and POS attributes, where the POS setting is interpreted as the circle center point. The center point and the preceding and following points define the plane of the arc. The choice of minor or major arc is governed by the arc which approaches closest to the conditioning point; the conditioning point need not lie in the plane of the arc. If RADS = false, the specified radius is ignored and the maximum radius is calculated to make sure that the nearest POINSP to the circle lies on the circle; the arc terminates on this point.

Note:
Displayed GENSECs treat each segment of the Spine as a separate extrusion. At the vertices between segments, i.e. at the POINSP positions, these extrusions merge together if there is a tangent continuity. If there is a tangent discontinuity, the extrusions are mitred along a plane normal to the mean of the two tangent vectors at the POINSP position.