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 BULG (bulge factor) 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 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 RADI (radius) 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 ensures 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 RADI (radius), CPOS (conditioning point) 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 ensure 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, that means, at the POINSP positions, these extrusions merge together if there is a tangent continuity. If there is a tangent discontinuity, the extrusions are miterd along a plane normal to the mean of the two tangent vectors at the POINSP position.