Axonometric projection

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Axonometric projection ("to measure along axes") ^[1] is a technique used in orthographic pictorials.

Within orthographic projection, axonometric projection shows an image of an object as viewed from a skew direction in order to reveal more than one side in the same picture, unlike other orthographic projections which show multiple views of the same object along different axes. Because with axonometric projections the scale of distant features is the same as for near features, such pictures will look distorted, as it is not how our eyes or photography work. Especially if the object to view is mostly composed of rectangular features, an axonometric view however is well suited for illustration purposes. ^[2]

The three types of axonometric projections are isometric projection, dimetric projection, and trimetric projection. Typically in axonometric drawing, one axis of space is shown as the vertical.

In isometric projections the direction of viewing is such that the three axes of space appear equally foreshortened, of which the displayed angles among them and also the scale of foreshortening are universally known. However in creating a final, isometric instrument drawing, in most cases a full-size scale, i.e., without using a foreshortening factor, is employed to good effect because the resultant distortion is difficult to perceive.

In dimetric projections, the directions of viewing are such that two of the three axes of space appear equally foreshortened, of which the attendant scale and angles of presentation are determined according to the angle of viewing; the scale of the third direction (vertical) is determined separately. Approximations are common in Dimetric drawings.

In trimetric projections, the direction of viewing is such that all of the three axes of space appear unequally foreshortened. The scale along each of the three axes and the angles among them are determined separately as dictated by the angle of viewing. Approximations in trimetric drawings are common.

[edit] References

^ Etymology from yahoo.com
^ Ingrid Carlbom, Joseph Paciorek (Dec. 1978), “Planar Geometric Projections and Viewing Transformations”, ACM Computing Surveys (CSUR) v.10 n.4: p.465-502, DOI 10.1145/356744.356750 .