hiddenline

Hiddenline, often referred to as hidden line, is a concept in technical drawing and computer graphics describing the suppression or concealment of lines that are not visible in the projected view of a three-dimensional object. It aims to produce clearer representations by showing only the edges and contours that can be seen from a given viewpoint.

In wireframe or line-rendered representations, visible edges are displayed while occluded edges are omitted or depicted with different conventions (such as dashed styles) to reduce visual clutter. Hiddenline is related but not identical to hidden-surface removal, which hides entire faces; hiddenline specifically targets line visibility and edge boundaries.

Algorithms used for hiddenline removal vary. Depth-based methods, including z-buffer approaches, test the visibility of edges against hidden geometry in raster images. Other techniques rely on depth sorting, painter’s algorithms, back-face culling, or ray casting to determine which edges are visible. Some systems also use projections and tolerance thresholds to handle ambiguous cases on curved surfaces or complex assemblies.

Applications of hiddenline techniques include computer-aided design and manufacturing (CAD/CAM), architectural drafting, engineering visualization, and geospatial displays. They are essential for producing legible technical drawings and for previews of 3D models in software that emphasizes outline clarity over shaded rendering.

History and development in the field of computer graphics trace hiddenline concepts to early 3D rendering efforts, with widespread implementation in CAD tools from the 1980s onward. Today, hiddenline remains a standard feature in many visualization pipelines, often configurable to balance accuracy and drawing legibility.

See also: hidden surface removal, wireframe rendering, line drawing, occlusion culling.