A plane is not just “traces”. It is defined geometrically by:
3 points not in a line.
2 lines that meet.
2 lines parallel.
1 line y 1 point outside it.
2. Traces of the plane
The traces (α₁, α₂) are the lines where the plane meets the PH and the PV.
The two planes the list usually forgets
Horizontal plane (parallel to the PH): it has no horizontal trace, it is at infinity; its vertical trace α₂ is parallel to the ground line. It is seen in true size in the plan.
Frontal plane (parallel to the PV): it has no vertical trace; its horizontal trace α₁ is parallel to the ground line. It is seen in true size in the elevation.
Notable lines of the plane
Horizontal: parallel to the PH; its elevation is parallel to the ground line.
Frontal: parallel to the PV; its plan is parallel to the ground line.
Steepest slope: perpendicular to the horizontal trace α₁; it measures the angle of the plane with the PH.
Steepest inclination: perpendicular to the vertical trace α₂; it measures the angle with the PV.
3. Full classification
1. Oblique plane (general)
Más común
2. Projecting planes
⊥ to a plane
One trace is perpendicular to the ground line.
3. Parallel to the ground line
Both traces are parallel to the ground line.
4. Profile plane
Necesita 3ª Vista
Both traces are perpendicular to the ground line (on the same line).
5. Through the ground line
Special
Its traces coincide with the ground line. It is defined by a profile point P.
The plane: how it is defined and how it looks
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Three points not in a line
Three points not in a line define a plane. Joining A-B and A-C gives two lines of the plane.