See section 11.15.8 for projections in the plane.
The projection command takes one or two arguments. The first argument is a geometric object. The second optional argument is a point. The command will project the point onto the object.
With one argument, projection returns a new command which
projects a point.
Input:
then:
returns and draws the point (1/3,1/3,1/3), which is the projection of (1,0,0) onto the line.
Input:
then:
returns and draws the point (0,1/2,1/2), which is the projection of the point (0,0,1) onto the plane.
With a second argument of a point, inversion
returns and draws the projection of the point.
Input:
returns and draws the point (1/3,1/3,1/3), as above.