While vector hardware has largely disappeared in favor of raster-based monitors and printers,[2] vector data and software continue to be widely used, especially when a high degree of geometric precision is required, and when complex information can be decomposed into simple geometric primitives. Thus, it is the preferred model for domains such asengineering,architecture,surveying,3D rendering, andtypography, but is entirely inappropriate[3] for applications such asphotography andremote sensing, where raster is more effective and efficient. Some application domains, such as geographic information systems (GIS) andgraphic design, use both vector and raster graphics at times, depending on purpose.
Vector graphics are based on the mathematics ofanalytic or coordinate geometry, and is not related to other mathematical uses of the termvector. This can lead to some confusion in disciplines in which both meanings are used.
Thelogical data model of vector graphics is based on the mathematics ofcoordinate geometry, in which shapes are defined as a set of points in a two- or three-dimensionalcartesian coordinate system, asp = (x, y) orp = (x, y, z). Because almost all shapes consist of an infinite number of points, the vector model defines a limited set ofgeometric primitives that can be specified using a finite sample of salient points calledvertices. For example, a square can be unambiguously defined by the locations of three of its four corners, from which the software caninterpolate the connecting boundary lines and the interior space. Because it is a regular shape, a square could also be defined by the location of one corner, a size (width=height), and a rotation angle.
Irregular three-dimensional surfaces and solids, are usually defined as a connected set of polygons (e.g., apolygon mesh) or as parametric surfaces (e.g.,NURBS).
In many vector datasets, each shape can be combined with a set of properties. The most common are visual characteristics, such as color, line weight, or dash pattern. In systems in which shapes represent real-world features, such as GIS and BIM, a variety of attributes of each represented feature can be stored, such as name, age, size, and so on.[4]
In some Vector data, especially in GIS, information abouttopological relationships between objects may be represented in the data model, such as tracking the connections between road segments in atransport network.[5]
If a dataset stored in one vector file format is converted to another file format that supports all the primitive objects used in that particular image, then the conversion can be lossless.
Vector-based devices, such as the vector CRT and thepen plotter, directly control a drawing mechanism to produce geometric shapes. Since vector display devices can define a line by dealing with just two points (that is, the coordinates of each end of the line), the device can reduce the total amount of data it must deal with by organizing the image in terms of pairs of points.[6]
Subsequent vector graphics systems, most of which iterated through dynamically modifiable stored lists of drawing instructions, include theIBM 2250,Imlac PDS-1, andDEC GT40. There was a video game console that used vector graphics calledVectrex as well as variousarcade games likeAsteroids,Space Wars,Tempest and many cinematronics titles such asRip Off, andTail Gunner usingvector monitors.[9] Storage scope displays, such as theTektronix 4014, could display vector images but not modify them without first erasing the display. However, these were never as widely used as the raster-based scanning displays used for television, and had largely disappeared by the mid-1980s except for specialized applications.
Plotters used intechnical drawing still draw vectors directly to paper by moving a pen as directed through the two-dimensional space of the paper. However, as with monitors, these have largely been replaced by thewide-format printer that prints a raster image (which may be rendered from vector data).
Because this model is useful in a variety of application domains, many different software programs have been created for drawing, manipulating, and visualizing vector graphics. While these are all based on the same basic vector data model, they can interpret and structure shapes very differently, using very different file formats.
Geographic information systems (GIS), which can represent a geographic feature by a combination of a vector shape and a set of attributes.[10] GIS includes vector editing, mapping, and vectorspatial analysis capabilities.
This vector-based (SVG format) image of a round four-color swirl displays several unique features of vector graphics versus raster graphics: there is noaliasing along the rounded edge (which would result indigital artifacts in a raster graphic), thecolor gradients are all smooth, and the user can resize the image infinitely without losing any quality.
TheWorld Wide Web Consortium (W3C) standard for vector graphics isScalable Vector Graphics (SVG). The standard is complex and has been relatively slow to be established at least in part owing to commercial interests. Many web browsers now have some support for rendering SVG data but full implementations of the standard are still comparatively rare.
In recent years, SVG has become a significant format that is completely independent of the resolution of the rendering device, typically aprinter or display monitor. SVG files are essentially printable text that describes both straight and curved paths, as well as other attributes. Wikipedia prefers SVG for images such as simple maps, line illustrations, coats of arms, and flags, which generally are not like photographs or other continuous-tone images.[citation needed] Rendering SVG requires conversion to a raster format at a resolution appropriate for the current task. SVG is also a format for animated graphics.
There is also a version of SVG for mobile phones called SVGT (SVG Tiny version). These images can count links and also exploit anti-aliasing. They can also be displayed as wallpaper.
CAD software uses its own vector data formats, usually proprietary formats created by software vendors, such asAutodesk'sDWG and public exchange formats such asDXF. Hundreds of distinctvector file formats have been created for GIS data over its history, including proprietary formats like theEsri file geodatabase, proprietary but public formats like theShapefile and the originalKML, open source formats likeGeoJSON, and formats created by standards bodies likeSimple Features andGML from theOpen Geospatial Consortium.
Modern displays and printers areraster devices; vector formats have to be converted to a raster format (bitmaps – pixel arrays) before they can be rendered (displayed or printed).[11] The size of the bitmap/raster-format file generated by the conversion will depend on the resolution required, but the size of the vector file generating the bitmap/raster file will always remain the same. Thus, it is easy to convert from a vector file to a range of bitmap/rasterfile formats but it is much more difficult to go in the opposite direction, especially if subsequent editing of the vector picture is required. It might be an advantage to save an image created from a vector source file as a bitmap/raster format, because different systems have different (and incompatible) vector formats, and some might not support vector graphics at all. However, once a file is converted from the vector format, it is likely to be bigger, and it loses the advantage of scalability without loss of resolution. It will also no longer be possible to edit individual parts of the image as discrete objects. The file size of a vector graphic image depends on the number of graphic elements it contains; it is a list of descriptions.
Vector art is ideal forprinting since the art is made from a series of mathematical curves; it will print very crisply even when resized.[12] For instance, one can print a vector logo on a small sheet of copy paper, and then enlarge the same vector logo tobillboard size and keep the same crisp quality. A low-resolutionraster graphic would blur orpixelate excessively if it were enlarged from business card size to billboard size. (The precise resolution of a raster graphic necessary for high-quality results depends on the viewing distance; e.g., a billboard may still appear to be of high quality even at low resolution if the viewing distance is great enough.)[13]
If we regard typographic characters as images, then the same considerations that we have made for graphics apply even to the composition of written text for printing (typesetting). Older character sets were stored as bitmaps. Therefore, to achieve maximum print quality they had to be used at a given resolution only; these font formats are said to be non-scalable. High-quality typography is nowadays based on character drawings (fonts) which are typically stored as vector graphics, and as such are scalable to any size. Examples of these vector formats for characters arePostscript fonts andTrueType fonts.
Because vector graphics consist of coordinates with lines/curves between them, the size of the representation does not depend on thedimensions of the object. This minimal amount of information translates to a much smaller[14]file size compared to large raster images which are defined pixel by pixel. This said, a vector graphic with a small file size is often said to lack detail compared with a real-world photo.
Correspondingly, one can infinitely zoom in on e.g., a circle arc, and it remains smooth. On the other hand, a polygon representing a curve will reveal being not really curved.
On zooming in, lines and curves need not get wider proportionally. Often the width is either not increased or less than proportional. On the other hand, irregular curves represented by simple geometric shapes may be made proportionally wider when zooming in, to keep them looking smooth and not like these geometric shapes.
The parameters of objects are stored and can be later modified. This means thatmoving,scaling,rotating,filling, etc. does not degrade the quality of a drawing. Moreover, it is usual to specify the dimensions in device-independent units, which results in the best possiblerasterization on rasterdevices.
From a 3-D perspective, rendering shadows is also much more realistic with vector graphics, as shadows can be abstracted into the rays of light from which they are formed. This allows forphotorealistic images andrenderings.
stroke line style and color (possibly transparent)
fill style and color (possibly transparent)
Vector formats are not always appropriate in graphics work and also have numerous disadvantages.[16] For example, devices such as cameras and scanners produce essentially continuous-toneraster graphics that are impractical to convert into vectors, and so for this type of work, an image editor will operate on the pixels rather than on drawing objects defined by mathematical expressions. Comprehensive graphics tools will combineimages from vector and raster sources, and may provide editing tools for both, since some parts of an image could come from a camera source, and others could have been drawn using vector tools.
Some authors have criticized the termvector graphics as being confusing.[17][18] In particular,vector graphics does not simply refer to graphics described byEuclidean vectors.[19] Some authors have proposed to useobject-oriented graphics instead.[17][20][21] However this term can also be confusing as it can be read as any kind of graphics implemented usingobject-oriented programming.[17]
Vector graphics are ideal for simple or composite drawings that need to be device-independent,[24] or do not need to achievephoto-realism. For example, thePostScript andPDFpage description languages use a vector graphics model.
Many stock photo websites provide vectorized versions of hosted images, while specific repositories specialize in vector images given their growing popularity among graphic designers.[25]
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