4- the theory of projection
TRANSCRIPT
The theory of projectionThe theory of projection
KCEC1101 CAD
ProjectionsProjections
Perspective or Perspective or Central Central
ProjectionsProjections
Parallel Parallel ProjectionsProjections
Linear Linear PerspectivesPerspectives
Aerial Aerial PerspectivesPerspectives
Oblique Oblique ProjectionsProjections
Orthographic Orthographic ProjectionsProjections
Projection MethodsProjection Methods
Projection MethodProjection MethodPerspective or Central Perspective or Central
ProjectionsProjections
Linear PerspectivesLinear Perspectives Aerial PerspectivesAerial Perspectives
Projection MethodsProjection MethodsParallel ProjectionsParallel Projections
Oblique Oblique ProjectionsProjections
Orthographic ProjectionsOrthographic ProjectionsAxonometric Axonometric ProjectionsProjections
MultiviewMultiviewProjectionsProjections
The attributes of each projection methodThe attributes of each projection method
Projection theoryProjection theory
Line of Sight (LOS)A LOS is an imaginary ray of light between an observer's eye and an object.
Projection theoryProjection theoryIn perspective projection, all LOS start at a single point
Projection theoryProjection theoryIn parallel projection, all LOS are parallel and no start point (infinitive viewpoint)
• A plane of projection is an imaginary flat plane upon which the image created by LOS is projected.
Projection theoryProjection theory
MultiviewMultiview projection planesprojection planes1. The frontal plane of projection is the plane onto which the
front view of multiview is projected.
MultiviewMultiview projection planesprojection planes2. The top view is projected onto the horizontal plane of projection,
which is a plane suspended above and parallel to the top object.
MultiviewMultiview projection planesprojection planes3. The right side is projected onto the right profile plane of
projection, which is a plane that is parallel to the right side of the object.
It produce the true dimensions !!!It produce the true dimensions !!!
Advantage of Advantage of multiviewmultiview drawingdrawing
Multiview drawing
Distorted angle
Distorted dimension
The six principal of viewsThe six principal of views
1. The front view
2. The top view
3. The right side view
4. The left side view
5. The rear view
6. The bottom view
The six perpendicular plane of viewsThe six perpendicular plane of views
Conventional view placementConventional view placementConventionally, the standard views used in a three-view
drawing are the top, front, and right side view. Because the other three principal views are mirror image and do not add to
the knowledge about the object.
Projection dimensionsProjection dimensionsThe width dimension is common to the front and top views. The height dimension is common to the front and side views. The depth dimension is common to the top and side views.
Projection arrangementProjection arrangement
The arrangement of views may vary as long as the dimension alignment is correct.
FirstFirst--Angle ProjectionAngle ProjectionFirst angle projection is the standard in Europe and Asia.
ThirdThird--Angle ProjectionAngle ProjectionThird angle projection is the standard projection for the United States and Canada.
The principal projection planes and quadrants used to create first- and third- angle projection drawings
Profile plane
The difference between first and third angle projection is the placement of the object and the projection plane
Pictorial comparison between firstPictorial comparison between first-- third angle third angle projection techniquesprojection techniques
First angle projectionFirst angle projection
The dihedral anglesThe dihedral angles
First angles projection boxFirst angles projection box
First angle projectionFirst angle projectionFirst angles projection boxFirst angles projection box
Box unfoldingBox unfolding
First angle projectionFirst angle projectionBox unfoldingBox unfolding
Box unfolded show Box unfolded show relative position of view relative position of view
Placement of 1Placement of 1stst
angle of viewangle of view
Third angle projectionThird angle projection
The dihedral anglesThe dihedral angles
Third angles projection boxThird angles projection box
Third angle projectionThird angle projection33rdrd angles projection boxangles projection box
Box unfoldingBox unfolding
Third angle projectionThird angle projection
Box unfoldingBox unfolding
Box unfolded Box unfolded show relative show relative
position of position of view view
Placement of 3Placement of 3rdrd angle of viewangle of view
The rule of orthographic The rule of orthographic projection principles projection principles
1. Alignment of features2. Distances in related views3. True length and size4. Foreshortening5. Configuration of planes6. Parallel features7. Edge views
Rule 1: Alignment of featuresRule 1: Alignment of features
• For example, the hole in the block is an example of a feature shown in one view and aligned on parallel projectors in the adjacent view
• Adjacent views are two orthographic view placed next to each other such that the dimension they share in common is aligned, using parallel projectors.
hole feature
Every point or feature in one view must be aligned
on a parallel projector
Rule 2: Distances in related viewsRule 2: Distances in related views
• For example, the distance between surface 1 and surface 2 is the same in the top view as it is in the right side view.
• Two views that are adjacent to the same view are called related views
Distances between any two points of the feature in
related views must be equal
Rule 3: True Rule 3: True length and sizelength and size
For example edge 1-2 in the top and right side view is a normal edge (or true-length line)
Features are true length or true size
when the lines of sight (LOS) are
perpendicular to the feature
An inclined line is parallel to a plane of projection, but inclined to the adjacent planes, it appears foreshortened in the
adjacent planes.
For example line 3-4 is inclined and foreshortened in the top and right side view, but true length in the front view, because it is parallel to the frontal plane of projection
Rule 4: ForeshorteningRule 4: ForeshorteningFeatures are foreshortening when the line of sight are not perpendicular to the features
• For example oblique line 1-2 is not parallel to any of the principal planes of projection of the glass box.
• An oblique line is not parallel to any principal plane of projection
Rule 5: Configuration of planesRule 5: Configuration of planesAreas that are the same feature will always be similar in configuration from one view to the next, unless viewed on edge
Surface B and C are an example of the Rule of Configuration of planes
Oblique surface
Incline surface
Rule 6: Parallel featuresRule 6: Parallel featuresParallel features will always appear parallel in all views
For example, at surface C, lines 3-4 and 5-6 are parallel in all views (front, top and right).
Also, edge 3-6 and 4-5 are parallel in both the top view and the right view.
Rule 7: Edge viewRule 7: Edge viewSurfaces that are parallel to the lines of sight will appear on edge and be represented as lines.
For example, surface A, C, D and F are parallel to the line of sight and will appear as on edges which represented as lines at projected front view.
Example of normal face projectionExample of normal face projection
A normal face projects on all three principle image planes. (follow the rule of edges view)
Creating a Creating a treetree--view view
sketchsketch
Example of representing filleted and rounded cornersExample of representing filleted and rounded corners
Example of Example of RunoutsRunouts
Representing the intersection of two cylindersRepresenting the intersection of two cylinders
Small cylinder Large cylinder(same size)
Representing the intersection btw a Representing the intersection btw a cylinder and a prismcylinder and a prism
Small prism Large prism
Representing the intersection btw a cylinder Representing the intersection btw a cylinder and a holeand a hole
Representing the intersection btw a cylinder Representing the intersection btw a cylinder and a slotand a slot
Center linesCenter lines
Good & Poor OrientationGood & Poor Orientation
The major surface are parallel or perpendicular to the sides of the box (projections planes)
The surface are not parallel to the sides of the glass box produces views with many hidden lines.
EndEnd