《机械制图及计算机绘图》英文课件-绘制直线的三面投影

主讲人：赵慧、杨国星TianjinLightIndustryVocationalTechnicalCollegeDrawingtheThree-ViewProjectionofaStraightLinePartIIn-ClassReviewPARTIIn-ClassReviewI.Three-ViewProjectionofaStraightLineDefinition：Astraightlineisdeterminedbytwopoints.Byconnectingthecorrespondingprojectionsofthesetwopointswithastraightlineineachview,weobtainthecorrespondingprojectionofthestraightline.aa

a

b

b

b●●●●●●In-ClassReviewII.ProjectionCharacteristicsofaStraightLineonaSingleProjectionPlaneAB●●●●abStraightlineperpendiculartotheprojectionplane:theprojectioncoincidesintoasinglepoint(AccumulationProperty)Straightlineparalleltotheprojectionplane:theprojectionreflectsthetruelengthofthesegmentab=AB(True-LengthProperty)Straightlineinclinedtotheprojectionplane:theprojectionisshorterthanthespatialsegmentab=ABcosα(SimilarityProperty).●●AB●●abαAMB●a≡b≡m●●●In-ClassReviewIII.ProjectioncharacteristicsofastraightlineinthesystemofthreeprojectionplanesProjection-plane-parallellinesProjection-plane-perpendicularlinesfrontalline—paralleltotheV-planeprofileline—paralleltotheW-planehorizontalline—paralleltotheH-planefrontalperpendicularline—perpendiculartotheV-planeprofileperpendicularline—perpendiculartotheW-planeVerticalline—perpendiculartotheH-planeGeneral‐positionstraightlinecollectivelyreferredtoasspecial-positionlinesStraightlineinclinedtoallthreeprojectionplanesPerpendiculartooneprojectionplanewhileparalleltotheothertwoprojectionplanes.Parallel

tooneprojectionplaneandInclinedtotheothertwoprojectionplanes.PartIIProjection-planeperpendicularlinesPARTIIProjection-planeperpendicularlinesProjection-planeperpendicularlines(⊥,∥,∥)1.Verticalline（⊥totheH-plane，∥totheV-plane，∥totheW-plane）b'b"a"BA0WHVXZb(a)a

b

b(a)a''b

ZXYWYHa'Projection-planeperpendicularlinesProjection-planeperpendicularlines(⊥,∥,∥)2.

Frontalperpendicularline（⊥totheV-plane，∥

totheH-plane，∥

totheW-plane）a'(b')b"a"BA0WHVXZYabXZYH0abb"a"a'(b')Projection-planeperpendicularlinesProjection-planeperpendicularlines(⊥,∥,∥)3.

Profileperpendicularline（⊥totheW-plane，∥totheV-plane，∥totheH-plane）a"(b")Wa'BA0HVXZb'abYWZYH0aba"(b")a'b'XYProjection-planeperpendicularlinesProjection-planeperpendicularlines(⊥,∥,∥)Projectioncharacteristics:(1)Onitsperpendicularprojectionplane,

theprojectionconvergesintoapoint.(2)Theprojectionsontheothertwoplanes,

reflecttheactuallengthofthesegmentandareperpendiculartothecorrespondingprojectionaxes.a

b

a(b)a''b

ZXYWYHb'(a)'baa

b

ZXYWYHa'b'aba''(b

)ZXYWYHIdentificationmethod:"Onepoint,twolines"–theprojectionthatisapointononeprojectionplaneindicatesitisperpendiculartothatprojectionplane.ProfileperpendicularlineFrontalperpendicularlineVerticallinePartIIIProjection-planeParallelLinesPARTIIIProjection-planeParallelLines（1）HorizontalLine（∥Hplane，∠Vplane，∠Wplane）

Projection-planeParallelLines(∥,∠,∠)）truelengthba''aa

b'b''ZXYHYWβγXZYOaa

b

a

bb

ABβγγβProjection-planeParallelLines（2）FrontalParallelLine（∥Vplane，∠H

plane，∠W

plane）Projection-planeParallelLines(∥,∠,∠)truelengthαγααXb"b'ba'a"aoZHWVABXaboa'b'ZYHb"a"YWYγγααProjection-planeParallelLines（3）ProfileLine（∥W

plane，∠V

plane，∠H

plane）Projection-planeParallelLines(∥,∠,∠)）truelengthXaba'b'ZYHb"a"YWob"b'ba'a"aZHWVABXYoαααβββProjection-planeParallelLinesProjection-planeParallelLines(∥,∠,∠)Projectioncharacteristics:Ontheprojectionplanetowhichthelineisparallel,itsprojectionshowsthesegment’struelengthandthetruemagnitudeoftheanglesbetweenthelineandtheothertwoprojectionplanes.

Ontheothertwoprojectionplanes,theprojectionsareparalleltotherespectiveprojectionaxes.Identificationmethod:“oneinclined,twoparallel”—theprojectionthatappearsinclinedonagivenprojectionplaneindicatesthatthelineisparalleltothatprojectionplane.b

a

aba

b

b

aa

b

ba

γAnglewiththeH-plane:α;anglewiththeV-plane:β;anglewiththeW-plane:γβγααβba

aa

b

b

HorizontallineFrontalparallellineProfileparallellinetruelengthtruelengthtruelengthProjection-planeParallelLinesProjection-planeParallelLines(∥,∠,∠)ProjectionCharacteristics:(1)Ontheprojectionplanetowhichthelineisperpendicular,projectionconvergestoapoint(i.e.,exhibitsconvergence).(2)Ontheothertwoprojectionplanes,theprojectionsrepresentthetruelengthofthelinesegmentandareperpendiculartotheirrespectiveprojectionaxes.a

b

a(b)a''b

ZXYWYHb'(a)'baa

b

ZXYWYHa'b'aba''(b

)ZXYWYHIdentificationMethod:"Onepoint,twolines"—Theplaneonwhichtheprojectionappearsasapointindicatesthatthelineisperpendiculartothatprojectionplane.ProfileperpendicularLineFrontalperpendicularlineVerticalline​PartIVLineinGeneralPositionPARTIVLineinGeneralPositionLineinGeneralPosition(∠,∠,∠)OXZYABbb

a

b

aa

ZXa

b''aOYHYWa

bb

Allprojectionsonthethreeprincipalplanesareinclinedstraightlines,andallofthemareshorterthanthetruelength.ProjectionCharacteristics:IdentificationMethod:"TripleInclination".PartVKnowledgeReinforcementPARTVKnowledgeReinforcementDeterminethepositionaltypeofeachofthefoll