Object - media.scc.losrios.edumedia.scc.losrios.edu/FitzpaK/books/Bk_AutoCAD_2008/Bk_AutoCAD_2008_Ch07.pdfobjects isdiscussed in AutoCAD andItsApplications—Advanced. Extension object

Learning Objectives

CHAPTER

ObjectSnaps and

After completing this chapter, you will be able to do thefollowing:/ Use objectsnap to create precision drawings./ Use objectsnap overrides for single point selections./ Set running object snap modes for continuous use./ Use the AutoSnap features to speed up point specifications./ Adjust marker size./ Use AutoTrack and temporary tracking modes to locate points relative to other

points in a drawing.

This chapter explains how the powerful object snap and AutoTrack™ featuresare used when creating and editing your drawing. Osnap means object snap. Objectsnap can be used to visually preview and confirm point options prior to selection.AutoTrack creates and deletes construction lines automatically. After these featuresareexplained, youwilllearnhowto take advantage oftheirstrengths whenyoucreategeometry.

c Object Snap )Object snap isone of the most useful tools inAutoCAD. Itincreases your drafting

performance andaccuracy. Snappingis theprocess ofpicking apoint near theintendedposition tohave thecrosshairs "snap" exactly to the specific point.

Object snap modes identify the object snap point. For instance, the Endpoint objectsnap mode automatically selects a line's endpoint, and the Midpoint object snap modeautomatically selects a line's midpoint. The AutoSnap™ feature provides visual cuesrelated to the active object snap modes. There are two methods of activating objectsnap modes: running object snaps and snap overrides. These topics are covered inmore detail in the following sections.

The AutoSnap feature is enabled by default. With AutoSnap active, visual cuesare displayed while snapping. This helps you visualize and confirm candidate pointsfor object snap. These visual cues appear as markers displayed at the current selection point. Figure 7-1 shows two examples of visual cues provided by AutoSnap. Thevisual cuefor an Endpoint object snap is a square thatappears when thecrosshairs is

snapping: Pickinga point near theintended position tohave the crosshairs"snap" exactly to thespecific point.

markers: Visual

cues to confirm

points for objectsnap.

217

218

Figure 7-1.AutoSnap displays markers and related tooltips for objectsnap modes.

Marker

(Endpoint)

Marker

(Tangent)

Tooltip

Snapping to an Endpoint Snapping to a Tangent

placed close to thelineobject. After a brief pause, a tooltip isdisplayed, indicating theobject snap mode. TheAutoSnap symbol for a tangency point is shownas a circle witha tangent horizontal line.

Object Snap ModesThe table in Figure 7-2 summarizes the object snap modes. Included with each

mode is the marker that appearson-screen and itsbutton from the ObjectSnap toolbar.Each object snap mode selects a differentportion of an object.

Remember that object snap overrides are not commands. They are,however, used in conjunction with commands. Ifyou type MID whenno command is active, for example, AutoCAD displays the followingerror message: Unknown command "MID". Press F1 for help.

Practice with the different object snap modes to find the ones that work best invarious situations. Be sure to clear thepreviousobject snap mode beforeactivating thenext one. Object snaps can be used during many commands, such as LINE, CIRCLE,ARC, MOVE, COPY, and INSERT. The most common uses for objectsnaps are discussedin the following sections.

Endpoint object snapIn many cases, you need to connect newgeometry to the endpoint ofan existing

line or arc. Select the Endpoint object snap mode and move the crosshairs past themidpoint of the line or arc, toward the end to be picked. A small square marks theendpoint thatwillbe picked. Pick tobegin drawing the new object. See Figure 7-3.

The Endpoint object snap can beused to quickly select theendpoints ofall typesof lines and arcs. It is often selected as a running object snap.

Midpoint object snapThe Midpoint object snap mode finds and picks the midpoint ofa line, a polyline, or

anarc. During a command, type MID, pick the Snap to Midpoint button ontheObject Snaptoolbar, or select Midpoint from the ObjectSnap shortcut menu to activate this objectsnapmode. Position the crosshairsnear the midpoint of the object. See Figure 7-4.

Exercise 7-1Complete the exercise on the Student CD.

AutoCAD and Its Applications—Basics

Figure 7-2.The object snap modes.

Mode Marker Button Description

Endpoint • / Finds the nearest endpoint of a line, arc, polyline,elliptical arc, spline, ellipse, ray, solid, or multiline.

Midpoint A /Finds the middle point of any object having twoendpoints, such as a line, polyline, arc, elliptical arc,polyline arc, spline, ray, solid, xline, or multiline.

Center o ©Locates the centerpoint of a radial object, includingcircles, arcs, ellipses, elliptical arcs, and radial solids.

Quadrant o IPicks the closestof the four quadrant points thatcan be found on circles, arcs,elliptical arcs,ellipses,and radial solids. (Not all of these objects may haveall four quadrants.)

••/

Intersection X X Picks the closest intersection of two objects.

ApparentIntersection

H ISelects a visual intersection between two objectsthat appear to intersect on screen in the currentview, but may not actually intersect each other in3D space.

Extension + —

Finds a point along the imaginary extension of anexistingline, polyline, arc,polylinearc, elliptical arc,spline, ray, xline, solid, or multiline.

Insertion *h Q> Finds the insertion point of text objectsand blocks.

Perpendicular h. J. Finds a point that is perpendicular to an objectfrom the previously picked point.

Parallel S //Used to find any point along an imaginary lineparallel to an existing line or polyline.

Tangent T5 oFinds points of tangency between radial and linearobjects.

Nearest X ALocates the point on an object closest to thecrosshairs.

Node 58J 0Picks a point object drawn with the POINT, DIVIDE,or MEASURE command.

None

Vft Temporarily turns runningobject snap offduring

the current selection.

Center object snap

The Center object snap mode allows you to snap to the center point of a circle,donut, ellipse, elliptical arc, polyline arc, or arc. During a command, type CEN, pickthe Snap to Center button on the Object Snap toolbar, or pick Center from the ObjectSnap shortcut menu.

Be sure to move the crosshairs near the perimeter, not the center point, of theobject. For example, when you locate the center of a large circle, the Center object snapmode will not locate the center if the crosshairs is not near the perimeter ofthecircle.See Figure 7-5.

Chapter 7 Object Snaps and AutoTracking 219

I

Figure 7-3.Using Endpoint object snap.

Existing If pick is madeline endpoint will

snap to here

First point ofnew line

Picking an Endpoint

Figure 7-4.Using Midpoint object snap.

Existingline

First pointof new line

Triangle marksmidpoint snap location

Picking a Midpoint

Figure 7-5.Using Center object snap.

Circle marks Existingsnap location circles


Picking a Center Point

Second point of new linesnapped to endpoint of

existing line

Completed Line

New line snapsto midpoint

Completed Line

New line snapscenter

Completed Line

Quadrant object snapquadrant: Quarter A quadrant is a quarter section ofa circle, donut, or ellipse. The Quadrant objectdonurofaneiiiise3 snaPmodefinds the°° 90° 180°'and270°Positionsonacircle'donut,ellipse,elliptical

arc, polyline arc, orarc. See Figure 7-6. When picking quadrants, move the crosshairsnear the intended quadrant on the circle, donut, ellipse, or arc.

220 AutoCAD and Its Applications—Basics

Figure 7-6.The four quadrant points ofa circle canbeselected with theQuadrant object snap.

Diamond marks New circle centeredExisting quadrant point on quadrant point

circle

180°

270c Picking a Quadrant Completed Circle

CQuadrant positions are unaffected by thecurrent angle zero direction, but they always coincide with the current world coordinatesystem (WCS). The WCS is discussed in Chapter 8. The quadrantpoints of a circle, a donut, or an arc are at the top, bottom, left, andright, regardless of the rotation ofthe object. Thequadrant pointsofellipses and elliptical arcs, however, rotate with the objects.


Intersection object snap

The Intersection object snap mode is used to snap to the intersection of two ormore objects. This mode isactivated by typing INT atthe selection prompt, picking theSnap to Intersection button on the Object Snap toolbar, or picking Intersection fromthe Object Snap shortcut menu. Move the crosshairs near the intersection to cause asmall "X" to appear at the intersection. SeeFigure 7-7.

Apparent Intersection object snap

The apparent intersection is the point where two objects created in 3D spaceappear to intersect based on the current view. Three-dimensional objects that are farapartmay appear tointersect when viewed from certain angles. Whether theyintersector not, this option returns the coordinate point where the objects appear to intersect.This is a valuable option when working with 3D drawings. Creating and editing 3Dobjects is discussed in AutoCAD andIts Applications—Advanced.

Extension object snap

The Extension object snap mode is used to find any point along the imaginaryextension of anexisting line, polyline, orpolyline arc. This mode is activated by typingEXT at theselection prompt, picking the Snap to Extension buttonon theObject Snaptoolbar, or picking Extension from the Object Snap shortcut menu. The Extensionobject snap differs from most other snaps because it requires more thanone selectionpoint. The initial point, called the acquired point, isnot selected in the typical manner,

Chapter 7 ObjectSnaps and AutoTracking

apparentintersection: Thepoint where twoobjects created in3D space appear tointersect based onthe current view.

acquired point:The initial pointpicked when usingobject snaps.

221

Iextension path:Dashed line or arc

that extends from

the acquired point tothe current location

of the crosshairs.

222

Figure 7-7.Using Intersection object snap.


Second point snapsto this intersection

Existing lineand arc

but is found by simply moving the crosshairs over the line, polyline, or polyline arcfrom which the new object is to be extended. When the object is found, a + symbolmarks the location. If the new object is to be created at the intersection of extensionsfrom two objects, the crosshairs must be placed over the second object to locate itsextension path.The lastpoint, which is the actualsnap point, canbe placed anywherealong the extension path, including the intersection of two extension paths. Theextension path, represented by a dashed lineor arc, extends from the acquired pointto the current location of the crosshairs.

Figure 7-8 shows an example of how the Extension object snap can create a newline anywhere along the extension of an existing object. The first acquired point isfound by moving the crosshairs directly over the upper-right corner of the rectangle.The tooltip for theextension is displayed, and the+marker becomes visible at theendof the line. While the dotted extension line is displayed, the first point can be picked.Thesecond acquired point is found in the samemanner at the endpointof the line ontheright. Pick neartheintersection oftheextension lines to locate thestart pointof thenew line.

TheExtension object snapcanalsobeused tocreate thenewlineaspecific distanceaway from the end of the old line. In Figure 7-9, the distance (.8) is typed while thefirst extension is displayed.

Figure 7-8.The Extension object snap canbe used tocreate a linefrom an extended intersection to anextended endpoint.

Acquire first Acquire secondextension point extension point

anddrag \ / anddrag

Stepl

Move crosshairs

to intersection

and pick

•———

Step 3

Acquiredfor endpoint

EEEH^EEa

Step 2

Step 4


Figure 7-9.Using the Extension object snap tocreate a line.8 units away from a rectangle.

Acquire pointand drag to specify

the direction

Type .8

Acquire secondpoint, dragand click


The finished line

' is .8 units awayfrom the rectangle

Extended Intersection object snap

One object snap—extended intersection—is available only as a snap override.When using Extended Intersection, you select the objects one at a time, and the intersection point is automatically located. This is useful when two objects do not actuallyintersect andyou need to access thepoint where these objects would intersect if theywere extended.

To activate Extended Intersection, select the Intersection object snap overrideand pick an object (rather than an intersection). If the crosshairs is near an object,but not close to an actual intersection, the tooltip reads Extended Intersection, and theAutoSnap marker is followed by an ellipsis(...). Figure 7-10 shows the use of ExtendedIntersection to find an intersection point between a line and an arc.

Figure 7-10.Finding theextended intersection oftwo objects. A—Select thefirst object. B—When thesecondobject isselected, the extended intersection becomes the snap point. C—The completed line.

Pick near the

first objectExisting

line


Pick near

second object

Completednew line

Chapter 7 Object Snapsand AutoTracking

New line

snaps to extendedintersection

extended

intersection:

Object snapoverride in which

the objects areselected one at

a time, and theintersection pointis automaticallylocated.

223

deferred

perpendicular:Calculation of theperpendicular pointis delayed untilanother point ispicked.

224

If the intersection point is not in the currently visible screen area, the AutoSnapmarker is not displayed when you select the second object. You can still confirm thepoint before picking, however. Keeping the crosshairs motionless over the secondobject displays the tooltip, which confirms that the objects intersect somewherebeyond the currently visible area. When selecting two objects that couldnot intersect,no AutoSnap marker or tooltip is displayed, and no intersection point is found if thepick is made.


Perpendicular object snapIn geometric construction, it is common to draw one object perpendicular to

another. Thisis done usingthe Perpendicular object snap mode. To activate this mode,type PER at theselection prompt, pick the Snap to Perpendicular button in the ObjectSnap toolbar, orpick Perpendicular from theObject Snap shortcut menu. Asmall right-angle symbol appears at the snap point. This mode can be used with arcs, ellipticalarcs, ellipses, splines, xlines, multilines, polylines, solids, traces, orcircles.

Figure 7-11 shows the Perpendicular object snap being used to locate the secondpoint of a line perpendicular to avertical line. InFigure 7-12, the object snap isused tostartthe line perpendicular to each object. The tooltip reads Deferred Perpendicular, andthe AutoSnap marker is followed byan ellipsis (...). The term deferred perpendicularmeans the calculation of the perpendicular point is delayed until another point ispicked. The second endpoint determines the location oftheentire line.

It is important to understand that perpendicularity is calculated from pointspicked and not as a relationship between objects. Also, perpendicularity ismeasuredat the point of intersection. Therefore, it is possible to draw a line perpendicular to acircle or arc.

Figure 7-11.Drawing a linefrom a pointperpendicular to anexisting line. ThePerpendicular objectsnap mode is usedto select the secondendpoint.

Figure 7-12.Deferring theperpendicularlocation until

the second pointis selected. ThePerpendicular objectsnap mode is usedto select the firstendpoint.

Existingline

Second pointwill snap so

lines are

perpendicular


Picking a Point Perpendicular

Existingline

Selecting anobject for _^_deferred

perpendicular

First pointlocated so

lines areperpendicular

New line perpendicularto existing line

Completed Line

Second

of new

pointine

Deferred Perpendicular Completed Line



Tangent object snap

TheTangent objectsnap is used toalign objects tangentially toan arc,circle,ellipse,elliptical arc, and spline.To activate this mode, type TAN at the selection prompt, pickthe Snapto Tangent button on the Object Snap toolbar, or pickTangent from the ObjectSnap shortcut menu.

In Figure 7-13, the endpoint ofa line is locatedusing the Tangentobjectsnap mode.The first point is selected normally. As the crosshairs is placed near the tangent pointon the circle, AutoCAD determines the tangent point and places the snap point there.

When you are creating an object tangent to another object, you may need to pickmultiple points tofix the tangency point. For example, thepoint atwhich a line is tangentto a circle cannot be found without knowing the locations of both ends of the line. Untilboth points have been specified, the object snap specification is for deferred tangency.Once both endpoints areknown, thetangency iscalculated, and theobject isdrawnin thecorrect location. In Figure 7-14, a lineis drawn tangent to twocircles.


Parallel object snap

The process of drawing, moving, or copying objects that are not horizontal orvertical is improved with the Parallel object snap mode. This option is used to findany point along an imaginary line that is parallel to an existing line or polyline. Toactivate the Parallel object snap mode, type PAR at the selection prompt, pick the Snapto Parallel button on the Object Snap toolbar, or pick Parallel from the Object Snapshortcut menu.

The Parallel object snap issimilar to the Extension object snap because it requiresmore than one selection point. The acquired point is found by pausing the crosshairsover any point on the line to which the new object is to be parallel. When the objectisfound andyou move thecrosshairs in a direction parallel to the existing line, a (//)symbol marks theexisting line. Adashed line, parallel totheexisting line, extends from

Figure 7-13.Using Tangent object snap.

Existing Point ofcircle \ tangency


Picking a Tangent Point

Chapter 7 Object Snaps and AutoTracking

Endpoint snaps so lineis tangent to circle

Completed Line

deferred tangency:Calculation of the

point of tangency isdelayed until bothpoints have beenpicked.

225

Figure 7-14.Drawing a linetangent to twocircles.

Start point will betangent to this circle

First Tangent Point Deferred

Endpoint will betangent to this circle

Picking Second Tangent Point

AutoCAD calculates

the point locations anddraws the new line

Completed Line

parallel alignment the location ofthe crosshairs. This line is known as the parallelalignmentpath.The lastpath:A dashedline, parallel tothe existing line,that extends from

the location of the

crosshairs.

point, which is theactual snap point, can beplaced anywhere along theparallel alignment path. When the alignment path is displayed, theParallel snap marker appears onthe line from which the parallel is used. Picking anylocation along the parallel alignment path creates the second point of the parallel line. Figure 7-15 shows an exampleof the Parallel object snap beingused to draw a line parallel to an existing line.

226


Node object snapYou can snap topoint objects using the Node object snap mode. Inorder for object

snap to find the point object, the point must bein a visible display mode. Controllingthe point display mode is covered in Chapter 8.


Figure 7-15.Using the Parallel object snap option to draw a line parallel to an existing line. A—Select thefirst endpoint for the new line, select the Parallel objectsnap, and then move the crosshairsnear the existing line to acquire a point. B—After the parallel point is acquired, move thecrosshairs near the location of the parallel line, and an extension path appears.

Acquired

Existing


Parallel snapmarker

Parallel alignment

New line

B

Nearest object snap

When you need to specify a point that is on an object, but cannot be located withany of the other object snap modes, you can use the Nearest mode. This object snaplocates thepointon the object closest to the crosshairs location. Use it when youwantan object to touch an existing object, but the locationof the intersection is not critical.

Consider drawing a line object that is to end on another line. Trying to pick thepoint with the crosshairs is inaccurate because you are relying only on your screenand mouse resolution. The line youdrawmay fall short or extend past the line. UsingNearest ensures that the point is precisely on the object.

Object Snap OverridesWhen youwant toactivate an object snap mode for a single point selection, use an

object snap override. Enter the object snap override whenyou are prompted to selecta point.This temporarily suspends any running object snap modes (whichare definedlater in this chapter). After you select the point, the running object snap modes arereactivated.

After you enter a command, an object snap override can be activated in any ofthree ways:

• Object Snap shortcut menu.Thisshortcut menu liststheobject snap modes. SeeFigure 7-16. To access the Object Snap shortcut menu when selecting a point,right-click and pick Snap Overrides or hold the [Shift] key and right-click.

• Object Snap toolbar. TheObject Snap toolbar includes a button foreachobjectsnap mode. See Figure 7-17. Pick the appropriate button to activate the snapoverride. To access this toolbar, right-click on any toolbar button and selectObject Snap from the shortcut menu.

• Keyboard entry. Each object snap override canbe activated by typinga three-letterabbreviation at a point selection prompt.

CUse the object snap modes not only when drawing, but also whenediting. With practice, using object snaps becomes second nature,greatly increasing yourproductivity and accuracy.

Chapter 7 Object Snapsand AutoTracking

object snapoverride: A

single, selectedobject snap modethat temporarilysuspends anyrunning object snapmodes.

227

| Object Snap |

ftOsnap Settings...

ITools> Drafting

Settings...

running objectsnaps: Objectsnaps that arealways active fordrawing commands.

228

Figure 7-16.The Object Snapshortcut menu

provides quickaccess to object snapoverrides.

Figure 7-17.The Object Snaptoolbar.

Temporarytrack point

—° Temporary track pant

f°EromMid Between 2 Points

Point Filters

/ Endpoint/ Midpoint/\ Intersection

^ Apparent Intersect—• Extension

® Center^ QuadrantO Tangent

_A_ Perpendicular

/? Para|elo Node

«4 Insert

A, Nearest

fcNone

(lu Osnap Settings.

Snap toIntersection

Snap toQuadrant

Object— snap override

options

Pick to access the

Object Snap tab ofthe Drafting Settings

dialog box

Snap to

Insert Snap toNearest

</V X&- ©# O -i/^g\ A& ft

rn

Snap toMidpoint

Snap toApparentIntersect

Snap to \ Snap toTangent \ Node

Snap to Snap toCenter Parallel

OsnapSettings..

Snap toNone

Running Object SnapsYou canset an object snap modeusing the Object Snap tab in the Drafting Settings

dialog box. To access thisdialog box, pick theOsnap Settings... buttonfrom theObjectSnap toolbar; pick Tools >Drafting Settings... from thepull-down menu; right-click onthe OSNAP or OTRACK button on the status bar and select Settings... from the shortcutmenu; or type OS, OSNAP, or DDOSNAP. You can also type DSETTINGS to access theDrafting Settings dialog box.

The Object Snap tab of the Drafting Settings dialog box is shown in Figure 7-18.Notice that the Endpoint, Intersection, Extension, and Parallel modes are active. Theobject snaps that are selected in this dialog box arecalled running object snaps. Youcan use this dialog box at any time to discontinue a running object snap or to setadditional modes.

When you need tomake several point specifications without the aidofobject snap,you can toggle running object snaps off by picking the OSNAP button on the statusbar. The advantage ofthismethod is thatyoucanmake several picks and thenrestorethesame running object snap modes by picking theOSNAP button again. You can alsopick the Object Snap On (F3) check box in the Drafting Settings dialog box or press the [F3]key onyour keyboard. Any of these options can beused to toggle running object snaps.

You can remove the active checks in the Drafting Settings dialog box as neededto disable running object snaps. You can also pick the Clear All button to disable allrunning modes. Select desired running object snaps by picking the associated boxesor pick the Select All button to activateall objectsnaps.


Figure 7-18.Running object snap modes can be set in the Drafting Settings dialog box.

c

Running objectsnaps activatewhen checked

Running objectsnap modes-are checked

Access the

Drafting tab ofthe Options "*dialog box

53Drafting Settings

Snap and Grid Polar Tracking Object Snap | Dynamic Inpulj

0 Object SnapOn(F3)

Object Snap mode?

• 0Endpoint

0 Object SnapTracking On(F11

A • Midpoint

O D Center

& rjNode

O • Quadrant

•0 Intersection

0 Extension

Ri Desertion

h_ 0 Perpendicular

C) 0 Tangent

X 0 Nearest

El O Apparent intersection

& 0 Parallel

!!»To track Irom an Osnappoint,pause overthe pointwhiteina

command. A trackingvector appears when you move the cursorTo stop tracking, pause over the point again

Options.. 3> Cancel

By default, a keyboard entry overrides any currentlyrunning objectsnapmodes. Thisbehavior canbe changed in the Priority for CoordinateData Entry area in theUser Preferences tab ofthe Options dialog box.

Exercise 7-8

C Complete the exercise on the Student CD.

Activates

all modes

Deactivates

all modes

AutoSnap SettingsTo customize theappearance and functionality oftheAutoSnap feature, access the

Object Snap tab of the Drafting Settings dialog box and pick the Options... button inthe lower-left corner. This opens the Drafting tab of the Options dialog box, showninFigure 7-19. To activate an AutoSnap option, check the corresponding check box:

• Marker. Toggles the AutoSnap marker display.• Magnet. Toggles the AutoSnap magnet. When active, the magnet snaps the

crosshairs to the objectsnap point.• Display AutoSnap tooltip.Toggles the tooltip display.• Display AutoSnap aperture box. Toggles the displayof the aperture.The marker color and size can also be adjusted to suit your needs. For example,

the default marker color is yellow, but this is difficult tosee if you have the graphicsscreenbackground set to white. Pick the Colors: button to access the Drawing WindowColors dialog box. Highlight the 2D model space selection in the Context: list and theAutosnap marker in the Interface element: list. Access the Color: drop-down list, andselect the desired color. Pick Apply &Close to return to the Options dialog box.

At higher screen resolutions, a larger marker size improves visibility. While theDrafting tab of the Options dialog box is still open, move the slider in the AutoSnapMarker Size area tochange the size. Ignore hatch objects determines whether you cansnap to hatch patterns. Hatching is discussed in Chapter 21.


aperture: Thesquare area withinwhich objects aredetected by objectsnap.

230

Figure 7-19.Setting AutoSnap features.

Select

options

Changemarker

color

Changemarker

size

AutoSnap Settings

0 Marker

J3 Magnet

0 DisplayAutoSnap tooltip

0 Display AutoSnap aperture box

Object Snap Options

0 Ignore hatchobjects

0 ReplaceZ valuewith cure

0 Ignore negative Z object si

Highlight theseoptions

AutoSnappreview

AutoTrackSettings

0 Display polar tracking vector

0 Display lull-screen tracking vectoi0 Display AutoTrack tooltip

Alignment PointAcquisition

©Automatic

O SMIlo acquire

|Drawing Window Colors

Context:

Shrfet / layouthe parallel projection

B 3D perspective projection" Block editor

Command linePlot preview

Interface element:

:ing tool tipDraftingtool tip backgroundLightglyphsLighthotspotLightfalloffLightstart limitLight end tmitCamera glyphs colorCamera frustum / frustum plane

Color:

• Color 31

Changeaperture

/ size

Select to

change theAutoSnapmarker color

Restore current element

Restore current context

Restore all contexts

| Apply &Close | Cancel | | Help |


Changing the aperture sizeWhen you select apoint using object snaps, thecrosshairs must bewithin aspecific

range ofacandidate pointbefore thepointis located. The object snapdetection systemfinds everything within a square area centered at thecrosshairs location. This squarearea is called the aperture and is invisibleby default.

To display the aperture, open the Drafting Settings dialog box and pick theOptions... button from the Object Snap tab. The Drafting tab of the Options dialogboxappears. Activate the Display AutoSnap aperture box check box. Having theaperturevisible maybe helpful whenyou are first learning to work with object snap.

To change the size of the aperture, move the slider in the Aperture Size area.Various aperture sizes are shown in Figure 7-20.


Figure 7-20.Aperture box size ismeasured in pixels.The three exampleshere are not shown

in actual size, butthey are providedto show the size

relationships amongdifferent settings.

5 Pixels 10 Pixels 20 Pixels

Keep in mind that the aperture and the pick box are different. The aperture isdisplayed on the screen when object snap modes are active. The pick box appears onthe screen for any command that activates the Select objects: prompt.


c AutoTrack )Creating geometry that lines up with existing geometry is very common in

drafting and design. AutoTrack makes this procedure straightforward and accurateby creating alignment paths and tracking vectors whenneeded. Alignment pathsaretemporary linesand arcs that coincide with the position of existing objects. Trackingvectorsare temporary lines that are displayed at specificangles, typically 0°, 90° 180°,and 270°.

The two AutoTrack modes are object snap tracking and polar tracking. Anycommands requiring a point selection, such as the COPY, MOVE, and LINE commands,can make use of these modes.

Object Snap TrackingObject snap tracking is always used inconjunction with object snaps. When this

mode is active, placing the crosshairs near an AutoSnap marker acquires the point.After a point is acquired, horizontal and vertical alignment paths are available forlocating points.

The [F11] function key and the OTRACK button onthe status bartoggle object snaptracking on and off. This mode is only available for points selected by the currentlyactive object snap modes. When running object snaps are active, all selected objectsnap modes are available for object snap tracking. These modes are not available forobject snap tracking, however, if running object snapsare deactivated.

In Figure 7-21, object snap tracking is used in conjunction with the Perpendicularand Midpoint running object snaps to draw a line that is 2 units long and perpendicular to the existing, slanted line. The running object snap modes are set before thefollowing command sequence is initiated. The OSNAP and OTRACK buttons on thestatus bar are active.


alignment paths:Temporary lines andarcs that coincidewith the position ofexisting objects.

tracking vectors:Temporary linesthat are displayed atspecific angles.

object snaptracking: Mode thatgives horizontal andvertical alignmentpaths for locatingpoints once a pointis acquired withobject snap.

231

232

Figure 7-21.Using object snap tracking to draw a line. A—Thefirst endpoint is located at the midpoint of theexisting line. The alignment path is displayed when the crosshairs are near. B—Thecompletedline, with the second endpoint identified using direct distance entry along the alignment path.


Alignmentpath

Command: L or LINEJ

Specifyfirst point: (pick the midpoint of the existing line)Specify next point or [Undo]: (pause the crosshairs near thefirst point to acquire it,

and then position the crosshairs as shown in Figure 7-21A to activate the perpendicular alignment path) 2J

Specify next point or [Undo]: JCommand:

Object snap tracking can also be used to position new geometry based on thelocationsof existing geometry. In Figure 7-22, objectsnap tracking is used to positiona circle directlyabove the midpointofa horizontal line and to the right of the midpointof an angled line, with only the Midpoint running object snap on. The OSNAP andOTRACK buttons on the status bar are active.

Figure 7-22.Object snap tracking is used to position this circle in linewith the midpoints ofeachline.

2. Pause the crosshairs over

the midpoint ofthe slanted line

1. Pause the crosshairs

over the midpoint of"" the horizontal line

3. Pick near intersectionto position the center

of the circle

4. Drag and pick tofinish the circle


C

Command: C or CIRCLEJ

Specifycenter point forcircle or [Undo]: (pause the crosshairs near the midpoint ofthe horizontal line toacquire it,arid then pause the crosshairs near the midpoint ofthe angled line toacquire it. Move the crosshairs to the position as shown in the second step of Figure 7-22 until two tracking vectors appear. Pick tolocate the centerof the circle.)

Specify radius ofcircle or [Undo]: (drag the crosshairs tospecify any radius and pickto complete the circle)

Command:

AutoTracking is similar in performance to the Extension object snap.Experiment with a combination of just the Endpoint object snap modeand AutoTracking. Try a combination of Endpoint and Extensionobject snap modes without AutoTracking to see the difference.Notice that without object snap tracking, you cannot drag in adirection perpendicular to an endpoint.


Polar TrackingOrtho mode,discussed in Chapter 3, forces the crosshairsmovement to orthogonal

(horizontal and vertical) orientations. When Ortho mode is turned on and the LINEcommandis in use,all newlinesegmentsare drawn at 0°, 90°, 180°, or270°. Polartrackingworks in much the same way, but it allows fora greaterrangeofangles.

Selecting the POLAR button from the status bar or using the [F10] function keyturns polar tracking on and off. You cannot use polar tracking and Ortho at the sametime. AutoCAD automatically turns Ortho off when polar tracking is on, and it turnspolar tracking off when Ortho is on.

When polar tracking mode is turned on, thecrosshairs snaps to preset incrementalangles if a point is being located relative to another point. For example, in the LINEcommand, polar tracking is not active for the first endpoint selection, but it is availablefor the second and subsequent pointselections. Polar tracking vectors are displayed asdashed lines whenever the crosshairsaligns with any of these preset angles.

To set incremental angles, use the Polar Tracking tab in the Drafting Settings dialogbox. To access this dialog box, right-click on the POLAR button from the status bar,and then select Settings; pick Tools > Drafting Settings... from the pull-down menu;or type DSETTINGS or DS. Figure 7-23 shows the Polar Tracking tab of the DraftingSettings dialog box.

The following features are found in the Polar Tracking tab:• Polar Tracking On (F10). Turns polar tracking on.• Polar Angle Settings area. Sets the desired polar angle increments. It contains

the following items:• Increment angle. Sets the angle increments at which polar tracking vectors

occur. Open the drop-down list to select from a variety of preset angles.Thedefaultincrementis 90, which provides angleincrementsevery 90°. Thesetting in Figure 7-23 provides polar tracking in 30° increments.


polar tracking:Mode that allows

the crosshairs to

snap to presetincremental anglesif a point is beinglocated relative to

another point.

233

234

Figure 7-23.The Polar Tracking tab of the Drafting Settings dialog box.

Activates /

polar tracking

Accesses Draftingtab of the Options

dialog box'

| Drafting Settings

SnapandGrid Polar Tracking ,Object Snap Dynamic Input

.—-0 Polar Tracking On (F10)

'olai Angle beltings

Incrementangle:

|30

• Additional angles

| New ]

| Delete |

Object Snap Tracking Settings

© Track orthogonally only

O Trackusingat polarangle settings

PolarAnglemeasurement

©Absolute

O Relative tolastsegment

[BIB

> Options.. OK Cancel Help

Adds polartracking to object

•^ snap tracking

Set polar snapincrements to

absolute or

relative

• Additional angles. Activates your own angle increments. To do this, pick theNew button to open a text box in the window. Type the desired angle. Pickthe New button each time you want to add another angle. The additionalangles are used together with the increment angle setting when you usepolar tracking.Use the Delete button to removeangles from the list.You can makethe additional angle(s) inactiveby turning off the Additional angles check box.

• Object Snap Tracking Settings area. Sets the angles available with object snaptracking. If Track orthogonally only is selected, only horizontal and verticalalignment paths are active. If Track using all polar angle settings is selected,alignment paths for all polar snap angles are active.

• Polar Angle measurement area. This setting determines whether the polarsnap increments are constant or relative to the previous segment. If Absoluteis selected, the polar snap angles are measured from the base angle of 0° setfor the drawing. If Relativeto last segment is selected, each increment angle ismeasured from a base angle established by the previously drawn segment.

Figure 7-24 shows a parallelogram being drawn with polar tracking active and set for30°angle increments and absolutepolar angle measurements. The followingcommandsequence creates the parallelogram:

Command: L or LINEJ

Specify first point: (select the first point)Specify next point or [Undo]: (drag the crosshairs to the right while the polar align

ment path indicates <0°) 3JSpecify next point or [Undo]: (drag the crosshairs to the 60°polar alignment path) 1.5JSpecify next point or[Close/Undo]: (drag the crosshairs to the 180° polar alignment path) 3JSpecify next point or [Close/Undo]: CJCommand:



Figure 7-24.Using polar tracking with 30°angle increments to draw a parallelogram. A—After the firstside is drawn, the alignment path and direct distance entry are used to create the secondside. B—A horizontal alignment path is used for the third side. C—Theparallelogram iscompleted with the Close option.

Alignmentpath

First

point

B

Polar tracking with polar snaps

Polar tracking can also be used in conjunction with polar snaps. If polar snapsare used when drawing the parallelogram in Figure 7-24, there is no need to type thelength of the line, because you set both the angle increment and a length increment.The desired angle and length increments are established in the Snap and Grid tab ofthe Drafting Settings dialog box. You can open this dialog box as previously described,or you can right-click on the status bar SNAP button and pick Settings... from theshortcut menu. This opens the Drafting Settings dialog box, as shown in Figure 7-25.

To activate polar snap, pick the PolarSnap button in the Snap type &style area ofthe dialog box. Picking this button activates the Polar spacing area and deactivatesthe Snap area. The length of the polar snap increment is set in the Polar distance: box.If the Polar distance: setting is 0, the polar snap distance will be the orthogonal snapdistance. Figure 7-26 shows a parallelogram being drawn with 30° angle incrementsand length increments of .75. The lengths of the parallelogram sides are 1.5and .75.

Figure 7-25.TheSnapand Grid tabof the Drafting Settingsdialogbox is used to set the polar snap spacing.

Activates

snap ~~

Polar snapspacing

Select grid orpolar snap ~

IDrafting Settings

Snap and Grid Polar Tracking Object Snap Dynamic Inputj

->»0SnapOn(F9)

Snap spacing

SnapX spacing

Snap Y spacing

0 5000

0 5000

0 Equal XandYspacing

Snap type

O Grid snap

• Rectangular snap

I:ometric snap

© PolarSnap

Options.,

• Grid On(F7)

Grid spacing

GridX spacing:

GridYspacing:

;Major lineevery: 5

I .

Grid behavior

0 Adaptive grid

• Allow subdivision below gridspacing

• Display grid beyond Limits

• Follow Dynamic UCS

Cancel

Chapter 7 Object Snaps and AutoTracking

0.5000

10.5000

Help

235

Figure 7-26.Drawing a parallelogram with polar snap.

mamm —

A B CD

Using polar tracking overrides

It takes some time to set up the polar tracking and the polar snap options, but itis worth the effort if you have several objects to draw that can take advantage of thisfeature. If you want to perform polar tracking for only one point, you can use the polartracking override to do this easily. This works for the specified angle whether polartracking is on or off. To activate a polar tracking override, type a left angle bracket(<) followed by the desired angle when AutoCAD asks you to specify a point. Thefollowing command sequence uses a 30° override to draw a line 1.5 units long:

Command: L or LINEJ

Specifyfirst point: (pick a start pointfor the line)Specify next point or [Undo]: <30JAngle Override: 30Specify next point or [Undo]: (move thecrosshairs in the desired 30° direction) 1.5JSpecify next point or [Undo]: JCommand:


AutoTrack SettingsThesettings that controlthe functionofAutoTracking can be accessed through the

Options... button on the Drafting Settings dialog box. This opens the Options dialogbox to the Drafting tab. This tab was illustrated in Figure 7-19.

The following options are available in the AutoTrack Settings area:• Display polartracking vector. Displays the alignment path. When this option is

off, no polar tracking path is displayed.• Display full-screen tracking vector. Extends the alignment path for object snap

tracking across the length of the screen. If this box is not checked, the alignment paths are shown onlybetween the acquired point and the crosshairs location. Polar tracking vectorsalwaysextend from the original point to the extentsof the screen.

• Display AutoTrack tooltip. Displays a temporary tooltip with the AutoTrackalignment paths.

The options in the Alignment Point Acquisition area determine how the objectsnap tracking alignment paths are selected:

• Automatic. Acquires points whenever the crosshairs is paused over an objectsnap point.

• Shift to acquire. Requires the [Shift] key to be pressed to acquire an objectsnappoint and use object snap tracking. AutoSnap markers are still displayed,and normal object snap can be used without pressing the [Shift] key. If manyrunning object snaps are set, you may want to use this option to reduce thenumber of paths displayed across the screen.


c Temporary Tracking )Other tracking modes are available in addition to those listed in the Object Snap

tab of the Drafting Settings dialog box. These modes may be used whether object snaptracking is on or off. These modes are Temporary track point, From, and Mid Between2 Points.

Temporary Track PointObject snap tracking has two requirements: running object snap mode must be

active and the crosshairs must pause over the selected point long enough to acquire it.Temporary track point can produce tracking vectors without either of these conditions.

To activate temporary tracking, pick the Temporary track point button from theObject Snap toolbar, type TT at the selection prompt, or pick Temporary track pointfrom the Object Snap shortcut menu. For example, temporary tracking can be usedto place a circle at the center of a rectangle. See Figure 7-27. The X coordinate of therectangle's center corresponds to the midpoint of the horizontal lines. The Ycoordinateof the rectangle's center corresponds to the midpoint of the vertical lines. Temporarytracking can be used to combine these two points to find the center of the rectangleusing this sequence:


Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: TTJSpecify temporary OTRACK point: MIDJof (pick one ofthe vertical lines and move the crosshairs horizontally)Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: TTJSpecify temporary OTRACK point: MIDJof (pick one of the horizontal lines and move the crosshairs vertically)Specify center pointfor circle or [3P/2P/Ttr (tan tan radius)]: (select the point where

the two alignment paths intersect)Specify radius of circle or [Diameter] <current>: JCommand:

The direction of the orthogonal line determines whether the Xor Ycomponent isused. In the previous example, after picking the first tracking point, the crosshairs ismoved horizontally. This means the Yaxis value of the previous point is being used,and tracking is now ready for an Xcoordinate specification.

After moving the crosshairs horizontally, you may notice movement is locked ina horizontal mode. If you need to move the crosshairs vertically, move it back to thepreviously pickedpoint,and then drag vertically. Usethis method wheneveryou needto switch between horizontal and vertical movements.

Figure 7-27.Using temporary tracking to locate the centerof a rectangle. A—The midpoint of the left lineis acquired. B—The midpoint of the bottom line is acquired.C—The center point of the circleis located at the intersection of the alignment paths.

A

-A-

B

Chapter 7 ObjectSnaps and AutoTracking 237

238

Using the From Point Selection OptionThe From point selection option is another tracking tool that can be used to locate

points based on existing geometry. It allows you to establish a relative coordinate, polarcoordinate, or direct distance entry from a specified reference base point. Access theFrom option by selecting the Snap From button in the Object Snap toolbar, selectingFrom in the Object Snap shortcut menu, or typing FROat a point selection prompt. Theexample in Figure 7-28 shows the center point for a circle being established as a polardistance from the midpoint of an existing line. The command sequence is shown here:


Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: FROJBase point: MIDJof (pick line)<Offset>: @2<45J

Specify radius of circle or [Diameter] <current>: (pick a radius)Command:

Using the Mid Between 2 Points OptionA point can be located at the midpoint of two picks by using the Mid Between 2

Points feature. This is different from the Midpoint object snap, which finds the midpointof a selected object. Mid Between 2 Points picks the midpoint between any two pointsin the drawing area and can be used in conjunction with object snap modes.

Mid Between 2 Points can only be accessed from the Object Snap shortcut menuor by typing M2P at a point selection prompt. The example in Figure 7-29 locates thecenter of a circle between two line endpoints:


Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: M2PJFirst point of mid: (select first point)Second point of mid: (select second point)Specify radius of circle or [Diameter] <current>: (pick a radius)Command:

Figure 7-28.Using the Frompoint selectionmode, following thecommand sequencegiven in the text.

Figure 7-29.Creating a circle,in which the center

is an exact equaldistance between

two points, usingthe Mid Between 2

Points option.

Midpointof line

First pick ofMid Between 2 Points

Center of circle at

midpoint betweenendpoints of lines

— Second pick ofMid Between 2 Points



platepment

Chapter 7

You will find that you need different object snaps and polartracking settings depending on the type of drawing you arecreating. These settings can be specified in your drawingtemplates to save time and increase efficiency. Refer to theStudent CD for detailed instructions to add these settings toyour mechanical, architectural, and civil drawing templates.

Chapter TestAnswer thefollowing questions. Write your answers on a separate sheet ofpaperorcomplete the electronic chapter test on the Student CD.

1. Define the term object snap.2. What is an AutoSnap tooltip?3. Name the following AutoSnap markers:

A1 B oc.

O

A

X

D.

£3E.

•F.

G.

+

H.

K.

O

SL.

4. Give the command and entries needed to draw a line to the midpoint of an existing line:A. Command:B. Specify first point:C. Specify next point or [Undo]:D. of

5. Define the term quadrant.6. What is the situation when the tooltip reads Extended Intersection?7. Give the command and entriesneeded to draw a line tangent to an existingcircle

and perpendicular to an existing line:A. Command:B. Specify first point:C. to

D. Specify next point or [Undo]:E. to

8. What does it mean when the tooltip reads Deferred Perpendicular?9. What conditions must exist for the tooltip to read Tangent?

10. What is a deferred tangency?11. Which objectsnaps depend on "acquired points" to function?

Chapter 7 ObjectSnaps and AutoTracking 239

77E

240

12. Describe the object snap override.13. If you are using running object snaps and you want to make a single point selec

tion without the effects of the running object snaps, what do you do?14. How do you activate the Object Snap shortcut menu?15. Define the term running object snap mode.16. How do you set running object snaps?17. How do you access the Drafting Settings dialog box to change object snap settings?18. If you are using running object snaps and want to make several point specifi

cations without the aid of object snap, but want to continue the same runningobject snaps after making the desired point selections, what is the easiest way toturn off the running object snaps temporarily?

19. Define the term AutoSnap.20. How do you change the color of the AutoSnap marker?21. How do you change the aperture size?22. Define the term AutoTracking.23. Which feature should be used in conjunction with AutoTracking?24. When are polar tracking vectors displayed as dashed lines?25. What are the two requirements to use object snap tracking?

Drawing ProblemsLoad AutoCADfor each ofthefollozving problems, and useoneofyour templates orstart a newdrawing using your own variables.

1. Draw the object below using the object snap modes. Do not draw the dimensions. Save the drawing as P7-1.

04.500

3X 02.000


2. Draw the highlighted objects below, and then use the object snap modes indicated to draw the remaining objects. Save the drawing as P7-2.

TAN

3. Draw the object below using the Endpoint, Tangent, Perpendicular, and Quadrantobject snap modes. Save the drawing as P7-3.

©©

4. Use the Midpoint, Endpoint, Tangent, Perpendicular, and Quadrant object snapmodes to draw these electrical switch schematics. Do not draw the text. Save the

drawing as P7-4.

Knife Switch

V <^>

Pressure Switch

(Start on Rise in Pressure)


«-^

Maintained Contact

Pushbutton

V<M>

Level Switch

(Start on High Level)

m

241

242

5. Use object snap modes to draw this elementary diagram. Do not draw the text.Save the drawing as P7-5.

OUTDOOR

INDOOR

NC \ NO

9KV

1 500E

^X^ POWER TRANSFORMER5050 KVA

5 KVA240/120V

FANS

FANS

"^Hl Ir-^-j £ —^ - BUSWAY HTR

^N

120V

rfDHB

1100

T6. Draw the elbow shown. Save the drawing as P7-6.

7. Draw the elbow shown. Save the drawing as P7-7.

07.25

019.25


For Problems 8-13, use object snap modes and tracking to draw the objects shown. Do not drawdimensions. Save the drawing as P7-(problem number).

32 —— 32-

5X «>12 K0

4X R12

4^5)32

4X R6

9.

38

R50-

10.

10-

2X 025-

11.

R13.5 013.5

25.5

R102X 010


12.

-3.000-

.750 —R.125

.875-1

1.750

4.500.525

— .500

13.

NOTE: BLEND ALL UNDEFINED RADII


Documents

Object - media.scc.losrios.edumedia.scc.losrios.edu/FitzpaK/books/Bk_AutoCAD_2008/Bk_AutoCAD_2008_Ch07.pdfobjects isdiscussed in AutoCAD andItsApplications—Advanced. Extension object