How to Draw Line of Sight

I'm taking a visual approach to a technical topic and focusing on drawing from direct observation and from the imagination.

The principles of linear perspective are based on how we actually see objects and environments around us. Linear perspective is a Western understanding. Principles of diminishment — the reduced scale of objects at a distance and converging parallel planes, eye level, object points, and eyeballing angles and distances — were described during the Renaissance. I don't say developed, because we've always seen this way. The principles describe the way things actually are.

First, some background. Perspective is optical drawing in that it describes how we actually see things.We see in points, not in planes. While we deal with concepts of visual planes, conceptual planes and actual planes, we really focus only on one thing at a time. This is why our eyes are constantly moving throughout our visual field.

In linear perspective, we see from a single point of view or from a single vantage point. When we translate things in our visual field to the drawn picture plane, it has to make sense. We draw from a single point of view, and the resulting drawing or illustration requires viewers to take that same point of view. The same idea is true with photography and film.

In reality, there is too much visual information going on in our visual fields to see everything at once. So we edit. This relates to us seeing point by point, shifting focus from on thing to another. But it also relates to what we see. We will tend to overlook quite a bit of what's in front of us and focus instead on what we think is important.

In drawing, painting and photography, we focus on the things we think are important, and exclude the rest. This exclusion is known as editing, and takes place as we're observing. What's important is what gets included in our images.

Isometric projections and linear perspective

Linear perspective is not the only way to represent objects and spaces, and it's not alway the most useful method. When drawings need to communicate technical information, using isometric projections is a clearer way to depict things. From a linear perspective point of view, projection drawings appear distorted and spaces and objects warped.

For narrative illustration, visual development and architectural renderings, linear perspective is the most appropriate method because is communicates concepts and stories most accurately.

Assumptions

When using linear perspective, we need to follow some guidelines. Linear perspective assumes the following to be true:

• Both the viewer and the objects are stationary.
• We see from one point of view at a time. We cannot see multiple points of view at the same time. We need to move to a different position in order to see from another point of view.
• Linear perspective is logical, physiological, and mechanical. One you understand its principles, it becomes easy to observe and draw them.
• Linear perspective is geometry in volumetric illusion. It consist of angles, corners, edges and faces.
• The distance between our eyes is constant. When we look at anything we triangulate between both eyes and a point on an object or in space. This triangulation helps us determine the size and distance of an object.
• In same space objects can be seen in one-, two- and three-point perspective.
• Any drawing, painting or photograph is an estimation of what we actually see.

Vocabulary, Terms, and Principles

To get you going on the right track with linear perspective, here are some definitions you need to know:

Point of View
The angle at which we see an object or space. Three-dimensional objects require multiple points of view when drawn in order to fully understand their form.

Picture Plane
The boundaries and interior area of the drawing surface. I advise to draw the frame of reference – the boundary of the drawing…

Station Point
The position of the viewer in relation to the picture plane and what's in it.

Line of Sight
The direction you're looking. The relationship between you or the viewer to the objects being viewed. The lines of sight are always perpendicular to the picture plane.

Eye Level
The distance from the ground plane to the viewer's eyes.

Horizon
The farthest edge or end of the ground plane. When eye level is parallel to the ground plane, eye level and horizon meet. Contrary to popular understanding, eye level and horizon are not the same thing. But the horizon is usually seen at eye level.

Station Point
Where the viewer stands in relationship to the scene depicted. The farther the object is from the viewer, the narrow the line of sight on the picture plane, and the closer to eye level.

Vanishing Point
The point at which parallel lines converge at eye level.

Illusion of Depth
Our understanding of depth in a two-dimensional image is determined by the relative size or proportion, position and shape of objects in the picture plane.

Diminishment
Objects located farther from the viewer appear smaller than objects that are closer.

Vertical Placement
The vertical position of an object in the picture plane helps communicate its distance from the viewer.

Overlap
An indicator of spatial relationships. One thing is depicted in front of another.

Object Points
Landmarks on an objects used to determine position, angles, dimension.

Horizontal/Vertical
These are natural axes we use to understand, move in and relate to space and objects. The human body has built-in horizontal and vertical axes.

Cone of vision
From the center axis of our head, we see accurately about 30˚ to either side of direct center. Each eye enjoys 60˚ coverage, and overlaps 30˚ in the center of the cone of vision. Objects outside this cone appear distorted.

Including peripheral vision, we can see 150˚ horizontally without turning our head. Vertically, our vision is limited to about 140˚ due to our anatomy.

Perspective angles

There are 5 perspective angles. These angles are determined by whether or not the face of a cube is parallel or angled in relationship to the viewer's picture plane

One-point parallel occurs when you see one side of an object in the vertical plane. Horizontal and vertical angles of the face with be parallel to the edges of the picture plane.

Two-point parallel occurs when you see two sides of an object in the vertical plane and there's true symmetry in which one side exactly mirrors the other.

Two-point angular occurs when you see two sides of an object in the vertical plane and you see more of one side than another.

Three-point parallel or angular (not shown above) occurs when the object is high overhead or well below the ground plane, or when the viewer is elevated or standing below the ground plane.

In one-point and two-point perspective, vertical edges are always parallel to the vertical edges of the drawn picture plane.

Tips for drawing what you see:

Understand your lines of sight in relationship to objects, corners and edges within your visual field.
Use object points (corners and landmarks on objects) as cues for position and direction in space.
Find proportions by measuring and estimating, making comparisons of angles based on right angles and size in
relationship to other distances.

Related Reading:

How To Find Angles and Proportions In Linear Perspective

How To Draw Three-Point Perspective

How to Draw Line of Sight

Source: https://alvalyn.com/drawing-basics-visual-approach-linear-perspective/

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