Trace points

SŠ10 min

Where a line pierces π₁ and π₂ – and why a trace always sits on the ground line.

○Not Started
3D – space
x₁₂π₁π₂ABaa₂a₁MM₁M₂NN₂N₁
Monge drawing
x₁₂π₂π₁a₂a₁M₁M₂N₂N₁

Orbit the space

Notice: both M₂ and N₁ lie on the ground line. Hover them.
2

Theory

A line is determined by its two views – the front view a₂ and the top view a₁. The projection of a line is again a line, so the views of two of its points suffice.

A trace point is where the line pierces an image plane. The trace M lies on π₁ so its height is zero; the trace N lies on π₂ so its depth is zero.

This gives the rule you use in every construction: M₂ lies on the ground line and N₁ lies on the ground line. So you find the traces where a view of the line crosses the ground line.

3

Step-by-step construction

3D – what happens in space
x₁₂π₁π₂
Drawing – what you draw
x₁₂π₂π₁
1 / 6
4

Practice

Build the construction yourself

3D – what you have
x₁₂π₁π₂
Your drawing
x₁₂π₂π₁

What is the next step?

1 / 5

Choose the step that comes next. The drawing only advances on a correct choice.

Check your understanding

1

Where does the front view M₂ of the trace point M lie?

2

What is the trace point N of the line a?

3

How many trace points does a line in general position have?

5

Downloadable material

A PDF for this lesson is in preparation.

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