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5/26/2018 3D Graphical Projection
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5/26/2018 3D Graphical Projection
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plane). It is the projection type of choice for working drawings.
i. Axonometric projection
Within parallel projection there is a
subcategory known as Pictorials . Pictorials
show an image of an object as viewed from a
skew direction in order to reveal all three
directions (axes) of space in one picture.
Parallel projection pictorial instrument
drawings are often used to approximate
graphical perspective projections, but there
is attendant distortion in the approximation.
Because pictorial projections inherently have
this distortion, in the instrument drawing of
pictorials, great liberties may then be taken
for economy of effort and best effect. Parallel
projection pictorials rely on the technique of
axonometric projection ("to measure along
axes").
ii. Isometric projection
In isometric pictorials, the direction of viewing is such that the three axes of space
appear equally foreshortened, of which the displayed angles among them and alsothe scale of foreshortening are universally known.
All isometric drawings are made with the 30-60 triangle, and most of them are done
in angular "perspective" where the two sides make an angle of 120 degrees with
each other and 30 degrees with the horizontal. In isometrics all s ides that are parallel
stay parallel and will not vanish to a vanishing point if prolonged. There are neither
vanishing points nor foreshortening in isometric drawing. The difference between true
B. Pictorials
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perspective and isometric drawing is shown in the diagram 34, where A is the
perspective of a block and B is the isometric drawing of it. It is also shown clearly in
Figure 35 where C is the perspective and D the isometric drawing of the same thing.
The three vertical edges a, b, and c of the block are called isometric axes, and all
lines parallel to these edges are called isometric lines. Measurements can be madeon the main isometric axis (b) only, for all other lines are inaccurate because they
are not in true perspective.
Isometric drawing
Is made up of a series of parallel vertical lines and parallel 30 degree
lines
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It is usually drawn out with the aid of a 30/60 degree set square.
Isometric is 30 degrees only
Sometimes Isometric grid paper is used to aid the drawing
NOTE: THERE ARE NO HORIZONTAL LINES
iii. Oblique
projection
In oblique projections the
parallel projection rays are not
perpendicular to the viewing
plane as with orthographic
projection, but strike the
projection plane at an angle
other than ninety degrees. In
both orthographic and oblique
projection, parallel lines in
space appear parallel on the
projected image. Because of
its simplicity, obliqueprojectionis used exclusively
for pictorial purposes rather
than for formal, working drawings. In an oblique pictorial drawing, the displayed
angles among the axes as well as the foreshortening factors (scale) are arbitrary.
The distortion created thereby is usually attenuated by aligning one plane of the
imaged object to be parallel with the plane of projection thereby creating a true
click on Image
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shape, full-size image of the chosen plane.
Method of Drawing
Oblique projection is a method of drawing objects in 3 dimensions. It is
quite a simple technique compared to isometric or even perspective
drawing. However, to draw accurately in oblique projection traditional
drawing equipment is needed
The technique for drawing a cube in oblique projection is outlined
below, stage by stage. To draw it correctly in oblique projection three
main rules must be followed:
1.Draw the front or side view of the object.
2.All measurements drawn backwards are half the original
measurement.
3.45 degrees is the angle for all lines drawn backwards
A.Draw the front view. Remember to use a T-square and 45
degree set square.
click on Image
click on Image
http://1.bp.blogspot.com/-8Pjl-RhEIqI/TwDhav9WjXI/AAAAAAAAAIU/HyfW_I5ZOaA/s1600/obliq3.gifhttp://4.bp.blogspot.com/-fKkKZYHX984/TwDg_v0MUeI/AAAAAAAAAH0/7fqYkLaDMfY/s1600/obliq1.gifhttp://3.bp.blogspot.com/-xEPKTeGUtIg/TwDhBVOdXGI/AAAAAAAAAH8/_MDtiIqSifk/s1600/obl2.gif5/26/2018 3D Graphical Projection
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Posted by Ms.Amal Aljohani at 1:58 AM
B. Draw 45 degree lines from each corner of the square. The
distance of any lines drawn back at 45 degrees should be halved. For
example, a cube may have sides of 100mm but they must be drawn
50mm in length. This should mean that the cube will look more realistic
and in proportion
C.Draw 45 degree lines from each corner of the square. Thedistance of any lines drawn back at 45 degrees should be halved. For
example, a cube may have sides of 100mm but they must be drawn
50mm in length. This should mean that the cube will look more realistic
and in proportion.
click on Image
click on Image
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