Projections of a line
SŠ8 minThe projection of a line is again a line – two projected points suffice.
Orbit the space
Theory
The projection of a line is again a line. That single fact is why descriptive geometry is tractable at all: you never project infinitely many points, two are enough.
So the procedure is always the same – pick two points on the line, project them into both image planes and join them in each. You get the front view a₂ and the top view a₁.
Mind what actually determines the line: one view is not enough. A whole projecting plane full of lines shares that one view; only the pair a₁, a₂ picks yours.
Step-by-step construction
Practice
Build the construction yourself
What is the next step?
1 / 4Choose the step that comes next. The drawing only advances on a correct choice.
Check your understanding
What is the projection of a line (in general position)?
How many of a line’s points must you project to construct its view?
Why is a single view not enough to determine a line in space?
Downloadable material
A PDF for this lesson is in preparation.
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