Various perspective models are used in technical illustration. Each of these models offers specific advantages. In the following section, you will learn background information on these models and learn their proper application.

From the various perspective models offered by Technical Illustration, you should select the appropriate one in accordance to what you would like to represent. These perspectives differ in the view used to depict the drawn body. Imagine different bodies and their representation method: For example, it is reasonable to depict an operating unit from the front. However, another object may be illustrated best when the spectator can see as many details as possible from the top surface of the object.

In practice, there are mainly used two perspective models: isometry and dimetry.

Isometry

Data:

The angles # and # are equal and amount to 30° each off the horizontal. The angle between the axes X, Y, Z amounts to 120°. The reduction factor amounts to 0.816 on all axes (X, Y, Z).
Isometry is used to furnish all three views with equal visual relevance.

Isometry offers many advantages and therefore is the most common perspective in Technical Illustration. One of these advantages is the re-use of an already depicted view for the two other views. The following illustration clarifies this:

As you can see, the same screw is used in all 3 views (iso = equal). It only needs to be drawn once and is then duplicated. By rotating it 120 ° it can be re-used to depict the two other views of the cube.

Dimetry

Data:

Angle # amounts to 7°, angle # amounts to 42° off the horizontal (precisely: # = 7°10', # = 41°25'). The angle between the axes X, Y, Z differs. The reduction factor is only taken into account on the X axis and there it amounts to 0.5.
Dimetry is used to emphasize one view of the represented object.

In dimetry, the three axes differ from each other. Therefore, it is not possible to re-use one element in another view by rotating its duplicates. Each element needs to be re-drawn in another view, as shown in our example below.

You can clearly see that the three screws differ from each other. You can also see that one view is emphasized.

This text is based on DIN ISO 5456-3 : 1996 and was created with the help of the "DIN-Taschenbuch 256, Zeichnungswesen 4, DIN ISO 4069 bis DIN ISO 14145-2". The paperback can be ordered from Beuth Verlag (publishing house), Germany.
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