Ch 5: Shaping Curves

AutoCAD 2012and

AutoCAD LT 2012 Essentials

By Scott Onstott

Ch 5: Shaping Curves

Drawing Polylines• Polylines can be composed of

linear and arc segments• Arcs swing counter clockwise by

default• When drawing arc segments, use

the Second Point option to swing arcs clockwise

• The Direction option can also swing polyline arcs clockwise

Ch 5: Shaping Curves

Polyline Arcs• Arcs can be chained together

using the PLINE command• Chained arcs form smooth curves• Arcs are sections of circles• Arcs can readily be dimensioned

with a radius length and center location

• Polyline arcs are much easier to survey than splines with variable curvature

Ch 5: Shaping Curves

Point objects• Point objects are helpful in planning

polyline arc curvature and as an aid in surveying

• Point objects have Node object snap• The display of point objects is

controlled by Point Style• Point Style is accessible with the

DDPSTYLE command

Ch 5: Shaping Curves

Editing Polylines• Polylines can be grip-edited or

edited using the PEDIT command• If you wish to change the

curvature of an arc segment beyond the curvature of a single arc, you must add an additional arc to the polyline

• Objects can be joined to polylines using the JOIN command, or the Join option within the PEDIT command

Ch 5: Shaping Curves

Ellipses and Elliptical Arcs• Elliptical arcs are sections of ellipses• Ellipses are created either by drawing two

perpendicular axes called Major and Minor, or by additionally specifying a center point

• Ellipses are constructed with a string and two fixed pins marking its foci in traditional drafting; this method is not represented in AutoCAD as its ellipses have no geometric foci or nodes to snap to

Ch 5: Shaping Curves

Distributing Blocks Along Curves• Use the DIVIDE and/or MEASURE

commands’ Block option to distribute items along a curved path

• The block is distributed based upon its insertion point, as defined in the block itself

• DIVIDE evenly spaces items along a path• MEASURE spaces blocks using a set

distance• The last increment created by MEASURE

is usually an unequal remainder

Ch 5: Shaping Curves

CV Splines• CV splines are typically roughed in at first

and their shape refined afterward• CV splines employ multi-functional grips that

allow you to stretch, add, remove, and refine control vertices

• Refining a control vertex converts a single CV into 2 adjacent CVs

• Refining CVs offers you more control over the shape of a CV spline

Ch 5: Shaping Curves

Editing Splines• Double click a spline object to invoke the

SPLINEDIT command• Use the Edit Vertex option in SPLINEDIT to

edit a CV spline• Use the Weight option inside Edit vertex

mode to adjust the weight value of individual CVs

• You can pull the spline closer to the control frame with higher weight values, and push it farther away with lower weight values

Ch 5: Shaping Curves

Fit Points Splines and BLEND• Fit point splines can have kinks• Add kinks using the Fit data option of SPLINEDIT• Move kink points to get sharp points in the spline• Use the BLEND command to create smooth CV curve

transitions between a variety of object types