Descriptive geometry exercises
Construction exercises in Monge projection and in space – from a point given by coordinates to the common perpendicular of skew lines. Every exercise is checked automatically and tells you which condition still fails. All are open – start anywhere.
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1Points and projections
A point from coordinates
Construct the point A[3; 2; 4].
SandboxBasicsA point in π₁
Construct the point B[−2; 3; 0]. Where is its front view?
SandboxBasicsA point in π₂
Construct the point C[1; 0; 3].
SandboxBasicsA point on x₁₂
Construct the point D[−3; 0; 0]. What is true of its projections?
SandboxBasicsA point in quadrant II
Construct any point Q lying in quadrant II (above π₁, behind π₂).
SandboxBasicsMirror image in π₁
Construct B, the mirror image of A[2; 3; 1.5] in π₁.
SandboxBasicsSegment AB
Construct the points A[−2; 1; 3], B[3; 4; 1] and the segment AB.
SandboxBasics
2Lines and planes
Traces of a line
Construct the horizontal trace P and the frontal trace N of line p = AB.
SandboxBasicsTraces below π₁
Construct the traces P and N of p = AB. Notice which quadrant N lies in.
SandboxBasicsParallel through a point
Through M draw the line q parallel to p = AB.
SandboxBasicsA line in a plane
Construct a line q lying in the plane ρ(4; 3; 5) and passing through its point M.
SandboxBasicsTraces of a plane
Construct the horizontal and frontal traces of α(−3; 4; 5).
SandboxBasicsHorizontal principal line
Through the point M of plane β = ABC draw the horizontal principal line h (parallel to π₁).
SandboxBasicsFrontal principal line
Through M[1; 1.5; 1.2] of plane β(5; 3; 4) draw the frontal principal line f (parallel to π₂).
SandboxBasicsLine of greatest slope
Through M[1; 1; 1.5] of plane γ(4; 4; 3) draw the line of greatest slope s with respect to π₁.
SandboxBasicsThe missing coordinate
The point A[2; 1; z] lies in the plane ρ(4; 4; 4). Construct it (find z).
SandboxBasicsPlane through a line and a point
Construct the plane σ through line p = AB and point M, and both of its traces.
SandboxBasicsPoints A, B, C in space
The classic maturita task: three points, a vector, a line, a plane and an angle.
3D Lab
3Positional problems
Line meets plane
Construct the point X where line p = AB pierces the plane ρ(4; 3; 5).
SandboxPositionalLine and triangle, visibility
Construct the point X where line p = MN meets triangle ABC. The visibility of p (dashed behind the triangle) is drawn automatically – check it in both views.
SandboxPositionalThe covering line (classical)
Find where p meets triangle ABC the classical way: the first projecting plane σ of p, the covering line k = σ ∩ ABC, then X = k ∩ p.
SandboxPositionalclassicalIntersection of two planes
Construct the intersection line r of planes α(4; 3; 5) and β(−3; 4; 2).
SandboxPositionalIntersection from the traces
Construct the intersection r of α(5; 4; 3) and β(−4; 3; 5) from the traces: R = meet of the horizontal traces, S = meet of the frontal traces, r = RS.
SandboxPositionalclassicalParallel to a plane and to π₁
Through M draw a line q parallel both to the plane ρ(4; 3; 5) and to π₁.
SandboxPositionalA parallel plane
Through M draw the plane σ parallel to ρ(3; 4; 2) and construct its traces.
SandboxPositionalNormal plane and its meet
Through M draw the plane ν perpendicular to p = AB and construct P = p ∩ ν.
SandboxPositionalMeeting a projecting plane
Construct the second projecting plane σ of line b, and the point X where line a meets σ.
SandboxPositionalDistance from a plane
Plane ABC and point M – the normal and the distance.
3D LabFoot of the normal
The orthogonal projection of a point into a plane.
3D LabLine meets plane
Line AB and plane PQR.
3D LabPlane from intercepts
A plane through three points on the axes.
3D Lab
4Metric problems
True length of a segment
Construct a segment equal in length to AB (for instance by rotating it into π₁).
SandboxMetricRotating the projecting plane
Classically: construct the first projecting plane σ of AB and rotate AB with it into π₁. The image (A)(B) has the true length.
SandboxMetricclassicalPerpendicular to a plane
Through M draw the perpendicular n to plane α and construct its foot F (where it meets α).
SandboxMetricDistance of a point from a plane
Find the distance of M from ρ(4; 5; 3): the normal n, its foot F, the segment MF and its true length d₀ in π₁.
SandboxMetricDistance of a point from a line
From M draw the perpendicular n to p = AB, construct its foot P and the segment MP.
SandboxMetricTrue shape of a triangle
Construct the true shape of triangle ABC by rotating its plane into π₁.
SandboxMetricInclination of a line to π₁
Find the inclination of p = AB to π₁.
SandboxMetricInclination of a plane to π₁
Find the inclination of ρ(4; 4; 2) to π₁ using the line of greatest slope through M.
SandboxMetricAngle of a line and a plane
Find the angle between p = AB and the plane ρ(4; 3; 5).
SandboxMetricAltitude of a triangle
In the space triangle ABC construct the altitude from C: the line h ⟂ c (c = AB) and its foot P on c.
SandboxMetricA plane perpendicular to a plane
Through p = AB pass a plane σ perpendicular to ρ(4; 3; 5).
SandboxMetricSection of a cube
A cube and three points on its edges - find the section and its area.
3D LabDistance of skew lines
Two skew lines and their distance.
3D LabAngle of two planes
The angle of two planes sharing a line.
3D LabAngle of a line and a plane
A line and the plane z = 0.
3D Lab
5Combined problems
Distance of parallel planes
Find the distance of α(4; 4; 4) and β(6; 6; 6): a common normal n, its meets A ∈ α, B ∈ β, the segment AB and its true length d₀ in π₁.
SandboxMetricTwo intersecting triangles
Construct the intersection line r of the planes of triangles ABC and KLM. Edge visibility is drawn automatically – check it agrees with r.
SandboxPositionalTransversal through a point
Through M draw the transversal q of the skew lines a, b – a line meeting both.
SandboxPositionalCommon perpendicular of skew lines
Construct the common perpendicular o of the skew lines a, b – a line meeting both at right angles.
SandboxMetricDistance from a line
The foot of the perpendicular and the distance.
3D Lab