projection method

8/7/2019 PROJECTION METHOD

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What do we mean by perspective?

�Perspective drawings show objects as you would

see them in the real world - in three dimensional

view.

�The lines of sight in a perspective drawing can be

projected to a vanishing point in the distance. This

is what gives the appearance of depth.

�Perspective drawings are a 3D representation of

an object but the proportions are not true they

are distorted to give the perception of depth.

�Also the detail at the farthest ends can be difficult

to see because it is so small.



Perspective Drawing



Disadvantages of a perspective drawing:

1. Only three sides of a component are shown.

2. No feature is a true proportion. They are not

drawn to a constant scale.

3. Sectioned perspective drawings are often

confusing.

4. Sometimes a hidden outline is shown which

can be confusing.

5. Dimensions are often difficult to show.



What is an isometric drawing?

�Isometric drawings are 3D drawings.

�They show three sides, all in dimensional

proportion, but none are shown as a true

shape with 90 degree corners.�All the vertical lines are drawn vertically but

all horizontal lines are drawn at 30 degrees to

the base line.

�Isometric is an easy method of drawing 3Dimages.



Isometric Drawing



Another method but rarely used

�Oblique drawings are also used in engineering.�The object is drawn with the most distinguishing

features facing directly towards the observer,

showing the true shape of these features.

�Circular features like round holes can be drawn onthis front face as true circles.

�In other 3D forms, circular features must be

drawn as ellipses.

�To show the 3D effect, parallel lines (called 'linesof sight') are drawn from the front face at an

angle.



The cavalier method is the simplest form of

oblique projection.



Isometric drawings

�give 3D views but don't give enough informationabout an object's true look because you can't see

the exact shape and size of each feature.

Orthographic projection� used to show a three dimensional object as a two

dimensional drawing.

�allows all possible views of a three dimensional

object to be shown in a two dimensional drawing.� uses multiple views of the object, taken from

points of view rotated about the object's center

through increments of 90°.



Orthographic Projection



First angle projection

�A method of creating a 2D drawing of a 3D object.

� It is mainly used in Europe and Asia and has not

been officially used in Australia for many years.

�The Australian Standard uses third angle

projection rather first angle projection as it is

easier to understand.



Note the symbol for first angle orthographic

projection. This is important information for theperson interpreting the drawing because if you

examine the diagram below you will note that in

first angle orthographic projection:



�the view from the front is in the middle�the view from the right is on the left

�the view from the left is on the right

�the view from the top is on the bottom

�the view from the bottom is on the top

�the view from the rear is on the far

right.



Third angle projection:

� is the preferred in USA and Australia



�the view from the left is on the left

�the view from the right is on the right

�the view from the top is on the top�the view from the rear is on the far right.



A drawing can have any combination of views but the

three most common views are:

�front view

�right side view, and�top view.



How do you show hidden detail in the drawing?

Many objects have internal features, such as

holes, slots and grooves. These features cannot be

seen when viewed side on in real life, but can be

represented as hidden outlines (ie dashed lines) in

drawings. Parts of an object may also conceal

other parts e.g. with a welded fabrication, and so

the hidden parts may be shown on a drawing as

hidden outlines.



How to show an outline of hidden features

projection method

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