ARC (ARC)

Attributes

Basic Creation Method

An ARC can be defined in three ways:

• by defining the positions of the end-points and a ‘through’ point (from which the values of Radius (RADI) and Angle Subtended (ASUB) can be derived if required).

• by defining the position of the center point, ‘from’ point and Angle Subtended (from which the position of the ‘to’ points and the value of RADI can be derived if required).

• by defining the position of the center point and two end points.

The method:

NEW ARC

DEF @

results in three points being prompted for (the ‘start’, ‘end’ and ‘through’ points). A line is drawn through the points and TCOD is set to ENDPOINT. A second method is available. See Positioning (absolute) (of an arc point) below for further information. If used with an existing ARC any existing values of RADI and ASUB are altered accordingly.

Defining or redefining an Arc with a center and two endpoints is achieved using the command:

ADEFine <dfnpt> <dfnpt> <dfnpt>

where <dfnpt> defines a position (2D, 3D, p-point).

The first two points are the center - (CPT) and ‘from’ point (FPT) of the Arc. These two points define the radius. The third point defines the angle subtended by the arc. The TO-point (TPT) lies in this direction from the center (CPT) at the same distance as the FPT from the CPT. The TCOD attribute is set to center.

The command can also be used with the cursor:

ADEFine @

A prompt requests three 2D points to be input for CPT, FPT and angle subtended. 3D points can also be input using the cursor:

ADEFine ID@ ID@ ID@

DEFine IDP@ IDP@ IDP@

Change Radius and Angle Subtended

RADIUS value [Design]

Sets RADI. For TCOD CENT this moves the ‘from’ and ‘to’ points radially (by the change in the value of the radius). center point position and ASUB are not altered. For TCOD ENDP this moves the ‘through’ point and changes ASUB; the positions of ‘from’ and ‘to’ points are unchanged.

RADIUS X value Y value

RADIUS E value N value U value

RADIUS IDP @

For TCOD ENDP this is like THPT @.

ASUBTENDED value [ANTICLOCKWISE]

ASUBTENDED value CLOCKWISE

Sets ASUB. (A positive angle is anticlockwise, a negative one clockwise.)

For TCOD ENDP this repositions the ‘through’ point (mid-way along the Arc) and changes RADI; ‘from’ and ‘to’ point positions are unaltered. For TCOD CENT this moves the ‘to’ point of the arc. center and ‘from’ points and radius are unchanged.

ASUBTENDED CLOCKWISE

ASUBTENDED ANTICLOCKWISE

Sets the value of ASUB to be negative or positive, respectively.

ASUBTENDED @

For TCOD ENDP this is like THPT @; For TCOD CENT this alters the angle subtended and hence moves the ‘to’ point of the Arc. The new position of the ‘to’ point lies on the line joining the center-point and the cursor position; center and ‘from’ points and radius are unaltered.

Position (absolute) (of an arc point)

The syntax is similar to that for FPTs of STRAs. Possible points are CPT (center point), FPT (‘from’ point), TPT (‘to’ point) and THPT (‘through’ point).

CPT @

The command changes the arc to be one with TCOD CENT (if not already so). The center is moved whilst keeping the ‘from’ point and ASUB unaltered. The ‘to’-point and radius are recalculated.

THPT @

The command changes the Arc to be one with TCOD ENDP (if not already so). The position of the ‘through’ point is moved whilst keeping the ‘from’ and ‘to’ points fixed - for example, both radius and angle subtended are altered.

FPT @

TPT @

For arcs with TCOD ENDP, the ‘from’ or ‘to’ point of the Arc (as appropriate) is moved whilst maintaining the positions of the other end point and the ‘through’ point.

For arcs with TCOD center, the ‘from’ or ‘to’ point of the Arc (as appropriate) is moved whilst maintaining the position of the center and the angle subtended. Thus the radius can change and the position of the other end point is moved to preserve the angle subtended.

Repeated Copy

See CIRCLE (CIRC) for further information.

Query

Similar to Straights, but referring to RADIUS, ASUBTENDED, CPT, FPT, TPT and THPT as appropriate. The Q IDN @ command can also be used.

Drag another primitive to which the Arc is connected

During the course of a DRAG operation on another primitive, the points of the Arc can move. The effect on the Arc is.

• For arcs with TCOD ENDP, Radius and Angle subtended are changed.

• For Arcs with TCOD CENT, if the center point is dragged, then the positions of the ‘from’ and ‘to’ points are also moved to preserve the Arc’s appearance.

• For Arcs with TCOD CENT, if an end point is dragged, then a rotation about the other endpoint takes place, for example, the center point is moved and the radius changed.