Development of Triangle Pyramid
A development, or rolled out, triangle pyramid. The image is created by making an arc at the bottom of each triangles to guide the straight lines. The triangle ABC is the base of the pyramid. When folded, the pyramid will form from the image.
Anthony, Gardner C. Elements of Mechanical Drawing (Boston, MA: D. C. Heath & Co., 1904)
Courtesy the private collection of Roy Winkelman