In mathematics, a hidden line is a geometric edge lineWeisstein, Eric W. "Polytope Edge". From Wolfram MathWorld. that is not visible from an observer's view of a solid shape or object.
A common practice is to draw the visible edges as solid lines and the hidden lines as dotted lines, dashed lines, software, Draw cube with dashed hidden lines. From TeX StackExchange. or thinner lines than the visible lines.
Hidden lines add geometric information about the unseen sides of an object. They are used to help a person visualize drawings of geometric objects in three-dimensional space."...needed to make the drawing clear", Hidden Lines and Centerlines, Modern Graphics Communication, 5th Edition
A three-dimensional object drawn with solid visible and hidden lines is a wire-frame model of the object.
Geometry objects without hidden lines
When a student is first introduced to a geometric cube, it's easier to start with something they are familiar such as a common box which is a cube without hidden lines. Drawing an object without hidden lines, matches an observer's view of the object. Omitting hidden lines makes an object easier to draw."Generally hidden lines can be omitted when they are not required for clarity.", Hidden Lines, Engineering Design Graphics
To draw higher dimensional cubes, hypercubes, without hidden lines, make the faces opaque. Then, the hidden lines are no longer visible, they are removed from the observer's view. This works with n-cubes in three-dimensional space.
Hidden lines in technical art
Hidden lines represent edges of a physical object that are not visible from a specific viewpoint. Visible lines are viewable edges from a specified viewpoint. In a technical drawing hidden lines are either included or not included, depending on the viewer’s requirement."Hidden lines are omitted from pictorial drawings unless they are needed...", Hidden Lines and Centerlines, Modern Graphics Communication, 5th Edition
"Hidden lines are used in engineering drawings to represent features that cannot be seen in a particular view but are necessary to fully define the part or assembly. Hidden lines are represented by a series of short dashes, evenly spaced, with the first dash in contact with the visible line from which it starts and the last dash in contact with the visible line at which it ends."Engineering Design Graphics, Line Conventions, and Hidden Lines, Robert Hewitt, Associate Professor at the University of Memphis
In a computer drawing application, the hidden line option may be referred to as a wire frame with hidden edges.Line Types in Technical Drawings YouTube video The wireframe hidden edges would be dashed lines.
Removing hidden lines is important in computer design and graphics applications. There are algorithmic solutions to remove hidden lines or partially hidden lines during an object's rendering. "The general problem of efficiently and meaningfully displaying three-dimensional objects in two dimensions is central to computer graphics."Perspective Drawing of Surfaces with Hidden Line Removal(in Spanish)Perspective Drawing of Surfaces with Hidden Line Removal(PDF English translation)
See also Hidden-surface determination Technical drawing Perspective Drawing of Surfaces with Hidden Line Removal The arXiv article is written in Spanish. PDF English translation.
References
External links What are the advantages and disadvantages of using dashed or dotted hidden lines?