Illustration for projecting a circle

thingiverse

I'm an educator teaching Descriptive geometry, and our current topic is drawing a circle on a given plane. The initial step involves rotating the plane to a horizontal position, ensuring that the circle appears in its true size. In parallel projection of a circle, it transforms into an ellipse with the major axis equal to the diameter of the circle. This major axis originates from the horizontal diameter of the circle and the minor axis is derived from the perpendicular diameter. The ratio between these two axes depends on the angle of the plane's slope. These visual aids help demonstrate the relationship between the original circle and its projected image.