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Transcription

True Length and True Shape

What is True Length?

True Length - Worked Example

Prism Examples

When we read the orthographic drawings of pyramids, are we seeing the true length of the sloping edges?

No, because the line 'sinks' back into the page.

Cylinder

Rectangular Prism

Triangular Prism

Plan

What is True Shape?

True Shape Worked Example

Pyramid Examples

When we see the cut face of a prism or pyramid, does the plan or end elevation show the correct size of this face?

Cone

Hexagonal Pyramid

Square Based Pyramid

No, because the true lengths are not represented in these views.

None of the orthographic views look at the cut face at 90° so the true lengths are not seen.

True Shape

Plan

End Elevation

Elevation

True Shape

Elevation

End Elevation

No, because the ladder is at an angle against the wall, which we don't see when we're looking at it 'straight on'.

Elevation

End Elevation

Elevation

Imagine a ladder against a wall. Is this the true length of the ladder?

End Elevation

Only by looking at the cut face at 90° will we see the true shape.

90°

True Shape

End Elevation

Elevation

So, to see the true length we need to rotate the sloping edge so that we're looking at it at 90°. True lengths are longer than their vertical height shown on the elevation.

90°

True Length

Plan

True Shape

Elevation

End Elevation

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