Orthographic Orthogonal Projection

The standard method of representing a three-dimensional object in two-dimensional form, i.e. as a scale drawing on one plane, is by orthographic projection in which related views give the various aspects, viz.:

Plan Representation of the object on the horizontal plane, i.e. looking down. Front and side elevations Representation of the object on the vertical plane, i.e. level with the eyes.

Section The object cut through either on the horizontal or the vertical plane to show details which would not be visible in simple outlines of plan and elevation. Vertical sections are usually included in a side elevation projected from the front elevation, and horizontal sections included in the plan, although if the object is complex several such sectional drawings may be necessary.

All these drawings are to a convenient scale, but full- or half-size details are necessary for free-hand curves where a compass radius cannot be stated, or where the particular detail calls for amplification.

They can be projected from either the first dihedral angle (first angle drawings) or the third dihedral angle (third angle drawings), and 331:1 gives a typical layout using the first angle and drawn to a scale of 1/8 (11/2 in to the foot) or to metric scale. The details given show, at 331:lB, the front elevation of a simple wooden plinth with a circular recess on the face for an inlaid metal plaque; 331:1 A is the plan of the plinth showing a stepped housing for a statuette; and 331:lC a vertical side section on the centre-line XY (331:1 A). Full-size details of the stepped housing and the circular recess are shown in 331:lD and 331:lE and no further information should be necessary. Where the drawings are of complex objects, however, it may be necessary to add a three-dimensional project for clarification.

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