Definition: In Linear Perspective drawing, orthogonals are the diagonal lines that can be drawn along receding parallel lines (or rows of objects) to the vanishing point.
Orthogonal is a term derived from mathematics, meaning 'at right angles' and related to orthogonal projection, another method of drawing three-dimensional objects. The term is possibly applied to the vanishing lines used in perspective drawing as these are at right angles to the front plane when observing an object in one-point perspective, or at right angles to each other in two point perspective.
The frequently used term 'orthagonal' is in fact a mis-spelling of 'orthogonal' and is "not a word". Think orthodoxy, orthodontist, and you'll remember the correct spelling.
Also Known As: Convergence lines, vanishing lines
Common Misspellings: orthagonals
