pictorial_notes

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Pictorials
Pictorials are picture drawings that show more than one side of an object at the same time. There are many forms of pictorials. The most accurate form of pictorial drawing is perspective. This shows objects in the form that we see them, or that cameras photograph them. Perspective is a very complicated form of drawing to complete, so a number of other drawing types have been developed. The following sequence shows the basic types,

One Point Perspective
One point perspective is used to show simple objects.

One Point Perspective Example
Notice the horizon line and the single vanishing point. The object can also be on or above the horizon line.

Cabinet Projection
Cabinet projections are approximations of one-point perspective. To simplify drawing them, the perspective lines are replaced with lines at fixed angles so that they could be drawn with standard drafting instruments (T-Squares and triangles). The two common forms were:

45 Degree Projection
According to the 1946 publication of Audels Answers on Blueprint Reading, distances on the 30 degree projection were 2/3 normal size, and on the 45 degree projection were 1/2 normal size. This is a very old style and is seldom used today.

Two Point Perspective
Two point perspective is a common form for pictures and artwork. Three and more points are also very common. They are not used as frequently for technical drawings, except for illustrations. Illustrations usually are done to look realsitic and include shadows, shading, textures and color. Technical drawings are usually line drawings.

[[image:http://www.cdli.ca/depted/g7/images/pic04.gif width="436" height="152" caption="pic04.gif (16711 bytes)"]]
Notice the horizon line and the 2 vanishing points. The object can be on or above the horizon line. Technical drawings would most often be below as shown here.

Isometric
Isometric is an approximation of two-point perspective. As with cabinet projections, this form was developed to be drawn using standard drafting instruments. This form is widely used for technical drawings and is supported in all CAD programs. Autosketch, for example, has an isometric grid mode which makes it easier to draw isometric drawings.

Isometric Example
Note that all lines are either vertical or sloped at 30 degrees. Isometric drawings use full dimensions on all sides. Very complex drawings may be done relatively easily with isometrics