2. Characteristics of the main types

Here are some positive and negative features of each type:

(I) Orthographic

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Orthographic projections are trivial to calculate.

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Parallel lines in the object have parallel images.

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If a face is parallel to the viewplane, then its image is undistorted-you can even measure on it.

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A box-shaped object has a dull and uninformative image if some faces are parallel to the viewplane.

(II) Oblique

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Oblique projections are easy to calculate.

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Parallel lines in the object have parallel images.

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If a face on the object is parallel to the viewplane, then the image of that face is undistorted, as if seen straight-on. This is good for engineering purposes.

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Oblique projections give a good psychological impression of the object, since you can see some sides of the object even if one face is seen undistorted.

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Oblique projections don't correspond to reality, since in reality you can't see a face of a box undistorted (as if seen straight-on) and also see some sides of the box.

(III) Perspective

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Perspective projections correspond best to what the eye actually sees.

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Parallel lines in the object do not stay parallel in the image (except those that are parallel to the viewplane to start with).

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Every face of the object is distorted in size or shape during projection.

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Perspective projections are harder to calculate.