drawing and editing polylines and splines chapter 16...edt 310 - chapter 16 - drawing and editing...

EDT 310 - Chapter 16 - Drawing and Editing Polylines and Splines 1

Drawing and Editing Drawing and Editing PolylinesPolylines and and SplinesSplines

Chapter 16Chapter 16

Sacramento City CollegeEDT 310


ObjectivesObjectives

Use the PLINE command to draw polylinesand polyarcs.Edit existing polylines with the PEDITcommand.Describe the function of each PEDIT command option.Use the EXPLODE command to change polylines into individual line and arc segments.


ObjectivesObjectives

Draw and edit spline curves.Create a polyline boundary.


The PLINE CommandThe PLINE Command


PLINE CommandPLINE Command

The PLINE command can be accessed by:Picking the Polyline button in the Draw toolbar

ORSelecting Polyline from the Draw pull-down menu

ORType PL or PLINE at the Command: prompt.


PLINE Command PLINE Command -- The Arc option The Arc option



The Arc option of the PLINE commandIs similar to the ARC commandThe PLINE Width and Halfwidth options can be used to set an arc width.

The arc width can range from 0 up to the radius of the arc.



A polyline arc with different end widths is drawn by accessing the Width option and changing the width values.


Drawing a Continuous Drawing a Continuous PolylinePolyline ArcArc

A polyline arc continued from a previous line or polyline is tangent to the last object drawn.

The arc's center is determined automaticallyYou can pick a new center.



If a straight polyline is continued from a polyline arc, the arc's tangent direction remains the same as that of the previous line, arc, or polyline.

This may not be what you want. Specify a different setting with one of the PLINE Arc options.



Options:AngleCenterCloseDirectionRadiusSecond pt (second point).


Specifying the Included AngleSpecifying the Included Angle

You can specify the angle for a PLINE arc by using the Angle option.



When a polyline arc is continued from a drawn object, the center point is calculated automatically.You can to pick a new center point.The CEnter option allows you to specify a new center point for the arc.



If A is entered, the next prompt is:Specify included angle: (enter an included angle and press [Enter])

If L is entered, the next prompt is:Specify length of chord: (enter a chord length and press [Enter])


The Direction OptionThe Direction Option

The Direction option changes the bearing of the arc. It changes the default option of placing a polyline arc tangent to the last polyline, arc, or line. The Direction option functions much like the Direction option of the ARC command.


Drawing a Drawing a PolylinePolyline Arc by RadiusArc by Radius

Polyline arcs can be drawn by giving the arc's radius. Enter the Radius option inside the PLINEArc command.


ThreeThree--Point Polyline ArcPoint Polyline Arc


ThreeThree--Point Point PolylinePolyline ArcArc

A three-point polyline arc can be drawn by using the Second pt option.



The CLose option adds the last segment to close a polygonal shape.

Used inside the PLINE Arc command sequence closes the shape with a polyline arc segment, rather than a straight polyline.



Notice that CL is entered at the prompt line to distinguish this option from the CEnter option.


Presetting Polyline WidthsPresetting Polyline WidthsThe PLINEWID System Variable The PLINEWID System Variable


Presetting Presetting PolylinePolyline WidthsWidths

The PLINEWID system variable presets a constant width for polylines.

Enter PLINEWID at the Command: prompt and enter a new value.


Presetting Presetting PolylinePolyline WidthsWidths

Although objects drawn with the POLYGON command are constructed with polylines, they are not affected by the PLINEWID system variable.


Editing Editing PolylinesPolylines



Polylines are drawn as single segments.

Even though you draw connecting segments, AutoCAD puts them all together.

The result is one polyline treated as a single object.



When editing a polyline, you must Edit it as one object

ORDivide it into its individual segments.



These changes are made with the PEDITand EXPLODE commands.



The PEDIT command is accessed by:Picking the Edit Polyline button from the Modify II toolbar

ORBy typing PE or PEDIT at the Command: prompt,

ORBy selecting Polyline from the Modify pull-down menu.



You can also select a polyline and then right-click in the drawing area to display a shortcut menu.



Use the pick box to select a polyline to be edited.If you use the pick box on a wide polyline, you must place it on the edge of a polylinesegment, rather than in the center.



If the object you select is a line or arcobject (not a polyline), the following message is displayed:

Object selected is not a polylineDo you want to turn it into one? <Y>

Entering Y or pressing [Enter] turns the selected object into a polyline.



A group of connected lines and arcs can be turned into a continuous polyline by using the PEDIT Join option.



A polyline can be edited as a single object, or it can be divided into individual segments to revise each segment individually.



There is no default option for the PEDITcommand

You must enter one of the options.Pressing [Enter] returns you to the Command: prompt.


Opening and Closing a PolylineOpening and Closing a Polyline


Opening and Closing a Opening and Closing a PolylinePolyline

You may decide that you need to close an open polyline, or that you need to reopen a closed polyline.

These functions are performed with the Open and Close options of the PEDIT command.



If you select a polyline that is already closed after issuing the PEDIT command, AutoCAD displays the Open option along with the other PEDIT command options.

Use the Open option to open the polyline.



If you select an open polyline, the Close option is displayed instead of the open option.

Enter C to close the polyline.



The Open option is not displayed if you select a polyline that was closed bymanually drawing the final segment.

It is only available if the polygon was closed using the Close option of the PLINE command.


Joining Joining PolylinesPolylines to Other to Other PolylinesPolylines



Polylines, lines, and arcs that are connected can be joined to create a single polyline.

Using the Join option of the PEDITcommand.



This option works only if the polyline and other existing objects meet exactly.

They cannot cross.There cannot be any spaces or breaksbetween the objects.

Select each object to be joined



Once items have been joined into a continuous polyline, the polyline can be closed using the PEDIT Close option.


Changing the Polyline WidthChanging the Polyline Width


Changing the Changing the PolylinePolyline WidthWidth

The Width Option of the PEDIT command allows you to change a polyline width to a new width.


Editing a Polyline VertexEditing a Polyline Vertex


Editing a Editing a PolylinePolyline VertexVertex

The Edit vertex option of the PEDITcommand is used to

Edit polyline vertices and Points of tangency.



A polyline vertex is where straight polylinesegments meet.

A point of tangency is where straight polyline segments or polyline arcs join other polyline arcs.



When you enter the Edit vertex option, an "X" marker appears on screen at the first polyline vertex or point of tangency.



NextPreviousBreakInsertMove

RegenStraightenTangentWidtheXit

The Edit vertex option has 10 options



NextMoves the "X" marker on screen to the next vertex or point of tangency on the polyline.

PreviousMoves the marker to the previous vertex or point of tangency on the polyline.

BreakBreaks a portion out of the polyline.



InsertAdds a new polyline vertex.

MoveMoves a polyline vertex to a new location.

RegenGenerates the revised version of the polyline.

StraightenStraightens polyline segments.



TangentSpecifies a tangent direction for curve fitting when using the PEDIT Fit option.

WidthChanges a polyline segment width.

eXitReturns the PEDIT command prompt.



Only the current point identified by the "X" marker is affected by editing functions. The marker is moved

Clockwise using the Next option (N)Counterclockwise using the Previous option. (P)



If you edit the vertices of a polyline and nothing appears to happen, use the Regenoption to regenerate the polyline.


Making Breaks in a PolylineMaking Breaks in a Polyline


Making Breaks in a Making Breaks in a PolylinePolyline

You can break out a portion of a polylineby using the Break option after entering the Edit vertex option.

Use the Next or Previous option to move the "X" marker to the correct vertex.

AutoCAD accepts the highlighted vertex as the first break point.


Making Breaks in a Making Breaks in a PolylinePolyline

Move the marker to the vertex you want to designate as the second break point.

Enter G for Go.

AutoCAD removes the portion of the polyline between the two selected points.


Inserting a New Polyline VertexInserting a New Polyline Vertex


Inserting a New Inserting a New PolylinePolyline VertexVertex

Use the Insert vertex option to add a new vertex to a polyline.

Use the Next or Previous option to locate the vertex next to where you want the new vertex.


Moving a Polyline VertexMoving a Polyline Vertex


Moving a Moving a PolylinePolyline VertexVertex

The Move vertex option enables you to move a polyline vertex to a desired location.

This option is similar to the Insert option. Place the "X" marker on the vertex you want to move with Next or Previous.Then, enter the Move option and specify the new location.


Straightening Polyline Segments or Straightening Polyline Segments or ArcsArcs


Straightening Straightening PolylinePolyline Segments or ArcsSegments or Arcs

The Straighten vertex option allows you to straighten polyline segments or arcs between two points.

Place the "X" marker on the vertex you want to move with Next or Previous.Then, enter Straighten option.If the 'X" marker is not moved before G is entered, AutoCAD straightens the segment from the first marked point to the next vertex.


Changing Polyline Segment WidthsChanging Polyline Segment Widths


Changing Changing PolylinePolyline Segment WidthsSegment Widths

The Width vertex option is the only option that changes the starting and ending widths of an individual polyline segment. To change a segment width

Move the "X" marker to the beginning vertex of the segment to be altered.Enter the Width option and specify the new width.


Changing Changing PolylinePolyline Segment WidthsSegment Widths

The starting width default value is the current width of the segment to be changed.

The ending width default value is the same as the revised starting width.

Enter the Regen option to have AutoCAD draw the revised polyline.


Making Smooth CurvesMaking Smooth Curves



In some situations, you may need to convert a polyline into a series of smooth curves.

One example of this is a graph. A graph may show a series of plotted points as a smooth curve rather than straight segments. This process is called curve fitting.



Another example of this is a curved landscape border.

The landscape border can be drawn withstraight polyline segments and then converted to a smooth curve.



Use the PEDIT Fit option and the Tangentvertex editing option.



The Fit option allows you to construct pairs of arcs passing through control points.

You can specify the control pointsOR

You can simply use the vertices of the polyline.

Closely spaced control points produce a smooth curve.



Prior to curve fitting, each vertex can be given a tangent direction.AutoCAD then fits the curve based on the tangent directions that you set.However, you do not need to enter tangent directions.Specifying tangent directions is a way to edit vertices when the PEDIT Fit option does not produce the best results.



Use the Tangent vertex option to edit tangent directions.

Move the 'X" marker to each vertex to be changed.Enter the Tangent option for each specified vertex Enter a tangent direction in degrees

ORPick a point in the expected direction.The direction you choose is then indicated by an arrow placed at the vertex.



Continue by moving the marker to each vertex that you want to change.

Entering the Tangent option for each vertex .

Select a tangent direction.



Once the tangent directions are given for all vertices to be changed, enter the PEDIT Fit option.



You can also Enter the PEDIT commandSelect a polylineEnter the Fit option without adjusting tangencies if desired.



If the resulting curve does not look like what you had anticipated, enter the Edit vertex option.

Make changes using the various vertex editing options as necessary.


The PEDIT The PEDIT SplineSpline OptionOption


The PEDIT Spline OptionThe PEDIT Spline Option

When a polyline is edited with the PEDIT Fit option, the resulting curve passes through polyline vertices.



The PEDIT Spline option makes the resulting curve pass through the first and last control points or vertices only.

The curve pulls toward the other vertices(but does not pass through them).



The SPLINETYPE system variable determines whether AutoCAD draws cubic or quadratic curves.

Default = 6 = cubic5 = quadratic

Refer to page 597 in text.


Straightening All Polyline SegmentsStraightening All Polyline Segments


Straightening All Straightening All PolylinePolyline SegmentsSegments

The PEDIT Decurve option returns a polyline edited with the Fit or Spline options to its original form.

The information entered for tangent directions is kept for future reference.

You can also use the Decurve option to straighten the segments of a polyarc.


The Undo OptionThe Undo Option



If you make a mistake while editing a polyline, use the Undo option.

Using the Undo option more than once allows you to step backward through each option used.

Press [Enter] to return to the Command: prompt.



The UNDO command can also be used at the Command: prompt to undo the effects of the last PEDIT command.


The SPLINE Command The SPLINE Command



The SPLINE command is used to create a special type of curve called a “non-uniform rational B-spline” (NURBS).

A NURBS curve is a “true spline”.



To access the SPLINE command:Pick SPLINE button in the Draw toolbar

ORPick SPLINE from the Draw pull-down menu.

ORType SPL or SPLINE at the the Command: prompt.


Drawing Closed Drawing Closed SplinesSplines

Use the Close option to draw a closed spline.


The Fit Tolerance Specification The Fit Tolerance Specification

Different results can be achieved when drawing splines by altering the specifications used with the Fit Tolerance option.

drawing and editing polylines and splines chapter 16...edt 310 - chapter 16 - drawing and editing...

Documents