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represented as a line. This dimensional generalization correlates with tendencies in spatial cognition. For example, asking the distance between two cities presumes a conceptual model of the cities as points, while giving directions involving travel "up," "down," or "along" a road imply a one-dimensional conceptual model. This is frequently done for purposes of data efficiency, visual simplicity, or cognitive efficiency, and is acceptable if the distinction between the representation and the represented is understood, but can cause confusion if information users assume that the digital shape is a perfect representation of reality (i.e., believing that roads really are lines).
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primitives, because every polygon can be constructed from triangles. All other graphic elements are built up from these primitives. In three dimensions, triangles or polygons positioned in three-dimensional space can be used as primitives to model more complex 3D forms. In some cases, curves (such as
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support a basic set of geometric primitives: points, polylines, and polygons, only in two dimensional space and the latter two with only straight line interpolation. TIN data structures for representing terrain surfaces as triangle meshes were also added. Since the mid 1990s, new formats have been
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is a polyline that closes at its endpoints, representing the boundary of a two-dimensional region. The software is expected to use this boundary to partition 2-dimensional space into an interior and exterior. Some data models allow for a single feature to consist of multiple polylines, which could
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property or function of two-dimensional space, affording it a number of data modeling efficiencies over true 3-dimensional objects. A shape of any of these dimensions greater than zero consists of an infinite number of distinct points. Because digital systems are finite, only a sample set of the
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is a set of polygon faces in three-dimensional space that are connected at their edges to completely enclose a volumetric region. In some applications, closure may not be required or may be implied, such as modeling terrain. The software is expected to use this surface to partition 3-dimensional
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Frequently, a representation of the shape of a real-world phenomenon may have a different (usually lower) dimension than the phenomenon being represented. For example, a city (a two-dimensional region) may be represented as a point, or a road (a three-dimensional volume of material) may be
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specification. Common geometric primitive extensions include: three-dimensional coordinates for points, lines, and polygons; a fourth "dimension" to represent a measured attribute or time; curved segments in lines and polygons; text annotation as a form of geometry; and polygon meshes for
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the user will start with a cuboid, then use extrusion and other operations to create the model. In this use the primitive is just a convenient starting point, rather than the fundamental unit of modelling.
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the intervening shape of the line between adjacent points in the list as a parametric curve, most commonly a straight line, but other types of curves are frequently available, including
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points in a shape can be stored. Thus, vector data structures typically represent geometric primitives using a strategic sample, organized in structures that facilitate the software
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represents a three-dimensional surface by a connected set of parametric functions, similar to a spline or BĂ©zier curve in two dimensions. The most common structure is the
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surface is often spoken of colloquially as "2 1/2 dimensional," because only the upper surface needs to be represented. Thus, elevation can be conceptualized as a scalar
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A 3D package may also include a list of extended primitives which are more complex shapes that come with the package. For example, a
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is a subtype of polyhedron in which all faces must be triangles, the only polygon that will always be planar, including the
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collectively connect to form a single closed boundary, could represent a set of disjoint regions (e.g., the state of
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that draw the corresponding objects are called "geometric primitives" as well. The most "primitive" primitives are
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defined by two points at its foci, or three points at its center, vertex, and co-vertex.
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OpenGIS Implementation
Specification for Geographic information - Simple feature access
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developed that extend the range of available primitives, generally standardized by the
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the remainder of the shape at the time of analysis or display, using the algorithms of
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and more complicated curves), as well as shapes (boxes, arbitrary polygons, circles).
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A Conceptual
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that the system can handle (draw, store). Sometimes the
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features consisting of several disconnected points.
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522:21 (4): 66–113. doi:10.3138/D794-N214-221R-23R5.
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579:Peachpit.com Info On 3D Primitives
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233:Cartesian coordinate system
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237:Multipoint
150:dimension
128:triangles
78:geometric
480:See also
456:Various
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470:shaders
400:POLYVRT
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288:Polygon
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107:Modern
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278:, and
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90:sphere
41:, and
32:vector
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304:A 3D
229:Point
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159:Point
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