Geometry of Vision: Visual Triangles on a Surface
Two cones of vision lettered with bases, hypotenuse and cathetus of triangles
Two large diagrams show fans of fine straight lines descending from a point marked Visio (vision) to a base, forming a family of triangles. The left figure is captioned with the bases of the triangles, their hypotenuse and their cathetus (legs), and is titled the finding of the height of points perpendicularly on a surface. The right figure adds a proposed circle (circulus propositus) and a sought line (linea quesita) upon the surface (superfities), setting out the perspective geometry by which the eye projects a figure onto a plane.
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The pyramid of vision and its triangles
From a point marked Visio (vision) a fan of lines descends to a base, forming triangles whose bases, hypotenuse and cathetus are labelled. The construction is titled the finding of the height of points perpendicularly on a surface.
Proposed circle and sought line on the surface
The right figure, likewise issuing from Visio, involves the bases of the triangles, a proposed circle (circulus propositus) and a sought line (linea quesita) laid out along the surface (superfities).