2011

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15 
UsinginferredconstraintsautomaticallyappliescoincidentconstraintsforEndpoint,Midpoint,Center,
Node,andInsertionobjectssnaps.Forexample,ifyoudrawacirclebysnappingitscentertothe
midpointofaline,AutoCADautomaticallyappliesacoincidentcon straintbetweenthecenterofthe
circleandthemidpoint
oftheline.Ifyoumovethecircle,thelinegoeswithit.Thesamepowerful
functionalityappliestoeditingcommands.If,forexample,youcopytheinsertionofablocktothe
endpointofaline,AutoCADautomaticallyappliesacoincidentcon straintbetweenthosetwopoints.
Whenyoumovethe
line,theblockmaintainsitspositionattheendpointoftheline.
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Figure25.Editingwithinferredconstraints
Inadditiontocreatingpoint‐to‐pointcoincidentconstraintswiththepreviouslymentionedobjectsnaps,
youcanusetheNearestobjectsnaptoapplyacoincidentconstraintbetweenapointandanobject.For
example,ifyoudrawthecenterofacircleonalineusingtheNearestobjectsnap,
thecenterofthe
circlehastheflexibilityofmovinganywherealongthelineincludingthevirtualextensionoftheline.
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Figure26.Nearestobjectsnapwithinferredconstraints
ThePerpendicularandTangentobjectsnapsautomaticallyapplyperpendicularortangentconstraints
betweentheobjectbeingcreatedoreditedandtheobjectbeingsnappedto.Theyalsoapplyapoint‐to‐
pointorpoint‐to‐objectcoincidentconstraintifappropriate.UsingtheParallelobjectsnapautomatically
appliesaparallelconstraintbut
nocoincidentconstraintsareappliedsince,bydefinition,thetwo
objectsneverintersect.Whenyoudrawhorizontalorverticallinesandpolylinesegments,inferred
horizontalandverticalconstraintsautomaticallyapplytothosesegments.
Inferredconstraintsenhancethebehaviorofrectangles,fillets,andchamfersbyautomaticallyapplying
appropriategeometricconstraints.For
example,ifyoudrawarectangle(usingtheRECTANGcommand),
AutoCADautomaticallyappliesapairofparallelconstraintsandaperpendicularconstrainttotheclosed
polyline.Whenyoumodifythesizeand shapeoftherectangle,youcanrestassuredthatitwillremain a
rectanglewithparallelsidesandperpendicular
corners.Creatingafilletautomaticallyapplies coincident
andtangentconstraintsbetweenthenewlycreatedarcandtheexistingpairoflineshelpingmaintain