Chapter on Computer Aided Drafting CADr is entirely rewritten with inclusion of 50 self-interactive and self-learning practice modules. D Bhatt Engineering Drawing 50th edition — Study Comfort Perspective Projection The Perspective projection is the approximate representation on a flat surfaceof the image perceived by the eyes. The oblique projection is a simple type of graphical projection used for producing the pictorial and 2-D images of 3-D objects. Tech 1st year or Diploma courses. An engineering drawing, a type of technical drawingis used to fully and clearly define requirements for engineered items.
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It is a form of parallel projection , here the view direction is orthogonal to the projection plane, resulting in each plane of the scene appearing in affine transformation on viewing surface. It is further divided into Multiview Orthographic projections and Axonometric projection. This projection shows that the object as it looks from the front, right , left, top, bottom, or back, and are positioned relative to each other according to the rules of either first-angle or third-angle projection.
The 3-D object is projected into 2-D "paper" space as if you were looking at an X-ray of object : top view is under the front view, the right view is at the left of the front view. All views are not necessarily used, and determination of surface constitutes the front, back, top and bottom varies depending on projection used. Multiview Orthographic Projections With this projection , upto six pictures of an object are produced , with each projection plane parallel to one of the co-ordinate axes of object.
The views are positioned relative to each other according to either of two schemes - first angle or third angle projection. The appearances of views may be of as being projected onto planes that form a six-sided box around the object. Although six different sides can be drawn three sides of a drawing give enough information to make a three-dimensional object.
All these views are known as front view, top view and right side view. The views are used when an object contains some sort of the inclined plane. Using the auxiliary view allows for inclined plane to be projected in true size and shape.
The true size and shape of any feature in a technical drawings can only be known when the Line of Sight is perpendicular to the plane which is considered as reference. Despite of the fact that auxiliary views are projected onto planes which are inclined to the principal projection planes , they are still classified as orthographic-views.
The LOS are still parallel to each other and perpendicular to the plane of projection. Thus when reading lines on the object in this view adjacent to a principal view , the same rules apply to reading lines in adjacent principal-views.
To utilize this view to show a surface true size , a view must exist or be drawn where that surface appears as a line. It is not possible to show an oblique surface in a primary auxiliary view. Once a given view showing the surface as a line is identified.
Complete auxiliary views are not commonly drawn in industry. It is much more common to see partial auxiliary-views that show only TS features. Since most of the other surfaces will be fore-shortened , a complete auxiliary-view becomes more difficult to read. Isometric Projection The isometric projection shows the object from the angles in which the scales along each axis of the object are equal.
This plane is either turned down into the horizontal plane or is wheeled into the vertical plane. This projection is a type of axonometric projection. Here in both the oblique-projection and the orthographic-projection , parallel lines of source object produce parallel lines in the projected image.
Perspective Projection The Perspective projection is the approximate representation on a flat surface , of the image perceived by the eyes.
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