偏距曲线

Synopsis

obj list = OFFCRV/obj list1,{dist|height,ang},ref point[,STEP,n1][{,EXT[,n2]|,FILLET}][,GROUP]

Description

Allows you to create offset curves. These offset curves are created from a chainable list of planar curves consisting of lines, arcs, conics, and/or B-splines. The offset curves lie on the same plane as the curves in the object list, unless a height and angle are specified (height and angle creates a draft angle as the curves are offset).

The draft angle offset takes place perpendicular to the plane containing the original objects. The draft angle is measured from a line which is also perpendicular to the plane.

Conics and B-splines are offset as splines. The accuracy of the offset is defined by the step value.

Parameters

Parameter

Description

obj list1

A list or array of existing objects consisting of lines, arcs, conics, and/or splines. The objects must all lie in the same plane.

dist

A numerical value or variable which represents the offset distance. A positive distance is offset in the direction of the reference point (ref point, in the following field)

height

A numerical value or variable which represents the distance that the curves are offset. The distance is measured perpendicular to the plane containing the original curves.

angle

A numerical value or variable which represents the "draft angle". The angle is measured from a vector pointing away from, and perpendicular to, the plane containing the original objects.

ref point

An existing point which defines the positive offset direction. The direction points from the beginning end point of the first object in the object list to the reference point. If these two points are coincidental an error occurs.

STEP

Minor word that indicates that the value in the following field represents the chordal stepping distance along a conic or B-spline that establishes offset points to approximate the curve with a spline. The system offsets the curve at each of these points, using the offset distance (or height and angle) as measured along a vector which is normal to the curve at that point. The system then creates a spline through these points which approximates the curve. Using a small step value produces a more consistent spline, however, it also takes more time to calculate and produces more knot points in the resulting spline.

NOTE: The default step size is one unit in the measuring system (inch or metric).

n1

A positive numerical value which represents the step used to approximate conics during the offset operation.

EXT

Minor word that indicates that offset curves are to be extended to their intersections to maintain the connectivity of the set of offset curves.

n2

A positive numerical value which represents how far offset curves can be extended at each end to remain connected. The extension factor is a multiple of the offset distance.

For example, an extension factor of 2 allows the curve to be extended, at each end, up to 2 times the offset distance. If the maximum extension does not causes the curves to connect, the system adds a line to fill the gap.

FILLET

Minor word that indicates that the connectivity of offset curves is maintained by adding an arc where necessary. When you use fillet, the curves are not extended.

GROUP

Minor word that indicates that the offset curves are created in a group. See example below for important information on using the GROUP option.

Example:

When a GROUP option is used, a group is returned, i.e.:

Statement
grp1=OFFCRV/crvs(1..count), distan, refpt, FILLET, GROUP

And if you don't use the GROUP option, an Array is returned:

Statement

ary1=OFFCRV/crvs(1..count), distan, refpt, FILLET

Parameter	Description
obj list1	A list or array of existing objects consisting of lines, arcs, conics, and/or splines. The objects must all lie in the same plane.
dist	A numerical value or variable which represents the offset distance. A positive distance is offset in the direction of the reference point (ref point, in the following field)
height	A numerical value or variable which represents the distance that the curves are offset. The distance is measured perpendicular to the plane containing the original curves.
angle	A numerical value or variable which represents the "draft angle". The angle is measured from a vector pointing away from, and perpendicular to, the plane containing the original objects.
ref point	An existing point which defines the positive offset direction. The direction points from the beginning end point of the first object in the object list to the reference point. If these two points are coincidental an error occurs.
STEP	Minor word that indicates that the value in the following field represents the chordal stepping distance along a conic or B-spline that establishes offset points to approximate the curve with a spline. The system offsets the curve at each of these points, using the offset distance (or height and angle) as measured along a vector which is normal to the curve at that point. The system then creates a spline through these points which approximates the curve. Using a small step value produces a more consistent spline, however, it also takes more time to calculate and produces more knot points in the resulting spline. NOTE: The default step size is one unit in the measuring system (inch or metric).
n1	A positive numerical value which represents the step used to approximate conics during the offset operation.
EXT	Minor word that indicates that offset curves are to be extended to their intersections to maintain the connectivity of the set of offset curves.
n2	A positive numerical value which represents how far offset curves can be extended at each end to remain connected. The extension factor is a multiple of the offset distance. For example, an extension factor of 2 allows the curve to be extended, at each end, up to 2 times the offset distance. If the maximum extension does not causes the curves to connect, the system adds a line to fill the gap.
FILLET	Minor word that indicates that the connectivity of offset curves is maintained by adding an arc where necessary. When you use fillet, the curves are not extended.
GROUP	Minor word that indicates that the offset curves are created in a group. See example below for important information on using the GROUP option.