Vector Graphics Glossary
Vector graphics is the use of geometrical primitives such as points, lines, curves, and
shapes or polygons, which are all based on mathematical expressions, to represent images
in computer graphics.
Vector graphics are based on vectors (also called paths, or strokes) which lead through
locations called control points. Each of these points has a definite position on the x and y
axes of the work plane. Each point, as well, is a variety of database, including the location
of the point in the work space and the direction of the vector (which is what defines the
direction of the track).
PATH
The open or closed path is the basis for all vector objects. A path is
made up of one or more line segments connected by two or more
anchor points. Paths can be made from a combination of straight
lines and curves, each of which may be made up of many connecting
points. Paths can be open or closed. An open path is one with
unconnected end points, while a closed path is one whose start and
end points meet.
POLYGON
Any closed path made up of three or more adjoining line segments.
Vector drawing programs usually provide tools for drawing ellipses
(circles and ovals), squares and rectangles, and most have polygon
tools allowing you to automatically draw other shapes such as
triangles, stars or shapes with any number of sides. Once created,
basic polygons can be edited to form much more complex shapes.
RASTERISE
Rasterising is the process of converting an image from a vector
format to a raster (or bitmap) format. Vector images usually need
to be rasterised in order to print them or display them on the web.
Once rasterised, the individual components of the vector graphic
(paths, fills, strokes, text, etc) can no longer be edited. A vector
image that has been rasterised is like any other raster image in that
it is a ‘resolution-dependent’ matrix of pixels (i.e. it cannot be scaled
without loss of quality).
The conversion process is relatively straight forward, opening
or importing a vector image in most raster-based image editing
programs (such as Adobe Photoshop or Corel Paint Shop Pro) will
prompt the user to select pixel dimensions and resolution for the file.
You can also save or export vector images as bitmaps using vectorbased drawing programs (such as Adobe Illustrator or Corel DRAW
- see Vector Drawing Software for others).
STROKE
A stroke or outline is a path’s outline. A path can have multiple strokes
of varying widths. Strokes, like fills, can be coloured or patterned.
SVG
Scalable Vector Graphics. An open standard graphics file format
based on XML. SVG is text-based and, as the name suggests, fully
scalable. Most other vector formats cannot be displayed on the web
without first being rasterised. SVG is an open source non-proprietary
alternative to Adobe Flash, which allows users to create vector
objects, animated images, data-driven and interactive content that
can be delivered via the web. SVG can also be delivered via mobile
devices (e.g. phones and PDAs) and in print.
All major modern web browsers (including Mozilla Firefox, Internet
Explorer version 9 and above, Google Chrome, Opera, and Safari)
have at least some degree of support for SVG and can render the
markup directly.
Each track can be assigned a colour, a shape, a thickness and also a fill. This does not affect
the size of the files in a substantial way because all information resides in the structure; it
describes how to draw the vector.
Definition of terms
ANCHOR POINT
Node, end points or simply points are the basic components of a path.
Points appear at the start and end of a path and at every point at which
the path changes direction. Points connect each line segment and
determine the nature of the line’s curve. Each point can be moved to
adjust the shape of the path Points can be added or removed from existing
paths.
BÉZIER CURVE
A curved segment of a path is known as a Bézier curve (after French
mathematician Pierre Bézier). Bézier curves are defined by mathematical
equations - essentially, the coordinates of a curve can be calculated and
drawn by knowing the position of two end points and two control points.
CAP
The cap refers to the end of an open path, and the cap style can usually
be one of three types: butt cap - the path ends abruptly at the end point;
round cap - the end is rounded; or projecting cap (aka square cap) - the
path projects beyond the end point.
CONTROL HANDLE
Control points or handles appear when a path’s anchor point is selected.
Control handles give greater control and flexibility over how each point
and line segment is placed, and allow fine-tuning of the overall shape of
the path.
FILL
Can be applied to any area within a path. Fills can be single blocks of
colour, gradients or patterns.
JOIN
Two or more line segments meet with a join, and the join style can usually
be one of three types: miter join - the join has a sharp point; round join the join has rounded point; or bevel join - the join has a flattened point.
LINE SEGMENT
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Paths are made up of one or more line segments. A line segment comes
between two anchor points and is either a curve or a straight line.
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