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This workflow covers the calculation of shadows in perspective projection in the simplest possible case - those that result from a light source that is positioned parallel to the picture plane.
Uses Tool(s) Drafting Board
This tutorial defines an appropriate topic and goal, but fails to adequately cover the techniques required to meet this goal. A set of step-by-step images and tutorial videos are required.

Properly projecting shadows in hand-drawn perspectives is one of the more challenging tasks in technical drawing. The mastery of this technique reflects a high-level of understanding of graphic projection, and is an excellent grounding for 3d modeling techniques.

Depicting shadows that result from a light source positioned parallel to the picture plane is the simplest and most common shadow projection to add in perspective drawing. Typically the shadows would be either a 30, 45 or 60 degree angle relative to the view plane. The shadows and the horizontal lines in the perspective all use the same vanishing points which make the drawing much easy to produce. The limitations of this type of shadow projection is that the shadow casting is always contained on the left or right side of the object.

There are two main protocols:

1. The shadow cast by a vertical line on a horizontal plane is horizontal.
2. On parallel surfaces, a shadow is parallel to the line that cast it and therefore vanishes at the same vanishing point.

# Example 1

Simple Cube, sun angle 45 degrees parallel to the picture plane.

First, set adjustable triangle to 45 degrees. And construction lines to the right corners of the building where the shadow will be cast. Draw horizontal lines from the vertical members of the object to find the first corner of the shadow. Outline the rest of the shadow by connecting to the two vanishing points.

It is important not to leave a heavy shadow lines surrounding soft shadow shading. This makes it seem as though there is something different between the outline of the shadow and the shadow itself, which there isn't.

# Example 2

Gable Roof Building, sun angle 60 degrees parallel to the picture plane.

Following the same process as before, except this time there will be additional construction lines drawn on the object to calculate the shadow geometry on the surface.

# Example 3

Overhand, sun angle 45 degrees parallel to the picture plane.

# Example 4

(introduction): Oblique Light

Not as common as two light vanishing points are required. Show an example.

# Example 5

Artificial Light Example

Artificial lighting, such as a central ceiling light, can also create shadows in an interior perspective. This drawing is much simpler to calculate than the oblique shadows. As seen in this example, all of the shadow lines emanate from a single vanishing point as well as from the ceiling or floor construction lines.

# Resources

http://www.most.gov.mm/techuni/media/Ar_02011_5.pdf , very informative guide on producing shadows.

Richard Brown's 'Principles of Practical Perspective' of 1815