Oblique angle

Mathematical formula
As a formula, if the plane facing the viewer is xy, and the receding axis is z, then a point P is projected like this:
�(���)=(�+12�cos⁡��+12�sin⁡�0)
Where �  is the mentioned angle.
The transformation matrix is:
�=[1012cos⁡�0112sin⁡�000]
Alternatively one could remove one third from the leading arm projected off the starting face, thus giving the same result.
Military projection
In the military projection, the angles of the x and z-axis and y and z -axis are at 45°, meaning that the angle between the x-axis and the y-axis is 90°. That is, the xy-plane is not skewed. It is rotated over 45°, though.
Examples
Besides technical drawing and illustrations, video games (especially those preceding the advent of 3D games) also often use a form of oblique projection. Examples include SimCity, Ultima VII, Ultima Online, EarthBound, Paperboy and, more recently, Tibia.

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The figures to the left are orthographic projections. The figure to the right is an oblique projection with an angle of 30° and a ratio of ¹⁄₂.

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Potting bench drawn in cabinet projection with an angle of 45° and a ratio of 2/3.

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Pieces of fortification in cavalier perspective (Cyclopaedia vol. 1, 1728).

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How the coordinates are used to place a point on a cavalier perspective.

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Stone arch drawn in military perspective.

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Stone arch drawn in cabinet perspective.

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A representative Korean painting depicting the two royal palaces, Changdeokgung and Changgyeonggung located in the east of the main palace, Gyeongbokgung.

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Entrance and yard of a yamen. Detail of scroll about Suzhou by Xu Yang, ordered by the Qianlong Emperor. 18th century

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18th century plan of Port-Royal-des-Champs drawn in military projection

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A variation of military projection is used in the video game SimCity

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A 3D rendered magnetic resonance angiography, shown in an oblique projection in order to distinguish the aberrant subclavian artery