Isometric and perspective

Isometric drawings and perspective drawings are commonly used in technical drawing to show an item in 3D on a 2D page.

Perspective

Perspective drawings show an object in 3D getting smaller in the distance.

Single-point perspective - This shows an object from the front in a realistic way as it gets smaller going into the distance. The front view goes back towards a vanishing point, which is a point on the horizon line that all lines meet at.

A single-point perspective drawing of a simple 3D 'L' shape - the corners of the shape trace back to one vanishing point behind it.Single-point perspective

Two-point perspective - This shows an object from the side with two vanishing points. It gives the most realistic view of a product as it shows the item edge on, as we would see it. It is often used to produce realistic drawings of an object.

A two-point perspective drawing of a simple 3D 'L' shape - the corners of the shape trace back along a horizon to two vanishing points either side of it.Two-point perspective

Single-point perspective is often used by interior designers to show a view into a room, whereas two-point perspective is often used by architects to show realistic building ideas.

A single point perspective 3D line drawing of a modern kitchen with an island.

Interior design in single-point perspective

Isometric

Isometric drawings, sometimes called isometric projections, are a good way of showing measurements and how components fit together. Unlike perspective drawings, they don’t get smaller as the lines go into the distance.

There are three main rules to isometric drawing:

An isometric representation of a hollowed out cube alongside a simple smartphone. Their outlines are black and they have no colour.

Isometric drawings are used to show a graphical representation of a 3D object. They are used by architects and engineers to communicate their ideas to the client and manufacturer, showing the product or design to scale.

Example

Below are two cubes drawn in isometric:

A 60 mm x 60 mm x 60 mm isometric cube alongside a 30 mm x 30 mm x 30 mm isometric cube for calculating scale factor.
curriculum-key-fact
Scale factor = smaller length ÷ larger length

= 30 ÷ 60

= 0.5

This means the second cube has been drawn to half scale, also written as 1:2.

Question

Work out the scale factor of the smaller cuboid below:

A 40 mm x 40 mm x 80 mm isometric cuboid alongside a 30 mm x 30 mm x 60 mm isometric cuboid for calculating scale factor.

Scale factor = 30 ÷ 40 or 60 ÷ 80

= 0.75

Also represented as a factor 34 or a ratio 3:4.