Fundamentals of data representation: Vectors
Objects and properties stored mathematically.
| If you enjoy messing about with SVGs take a look at inkscape |
Vector graphics are made up of objects and their properties. An object is a mathematical or geometrically defined construct such as a rectangle, line or circle.
<rect ... />
<line ... />
<circle ... />
Each of these objects has properties to tell you the size, colour, position etc. Take a look at the next example to see how drawing lists are built from objects and properties.
| Rectangle | Circle | Combination | |
|---|---|---|---|
| Image |  |
 |
|
| Drawing List |
<rect x="14" y="23"
width="250" height="50"
fill="green"
stroke="black" stroke-width="1" />
|
<circle cx="100" cy="100" r="50"
fill="red"
stroke="black" stroke-width="5" />
|
<rect
width="100" height="80"
x="0" y="70"
fill="green" />
<line
x1="5" y1="5"
x2="250" y2="95"
stroke="red" />
<circle
cx="90" cy="80"
r="50"
fill="blue" />
<text x="180" y="60">
Un texte
</text>
|
| Notes | x and y give the top left start location | Note that the centre co-ordinate is defined through cx and cy r gives the radius |
Note that the circle is on top, this is because it was drawn last. To leave out an edge stroke don't put the stroke command in. The line has start x1,y1 and end x2,y2 coordinates. |
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Extension:SVG There are several vector graphic formats out there, but an easy one to get started with is Scalable Vector Graphics (SVGs). SVGs are very easy to create and are supported by all modern major web browsers. To create an SVG, you need to add the tags <svg xmlns="http://www.w3.org/2000/svg">
<rect
width="100" height="80"
x="0" y="70"
fill="green" />
<line
x1="5" y1="5"
x2="250" y2="95"
stroke="red" />
<circle
cx="90" cy="80"
r="50"
fill="blue" />
<text x="180" y="60">
Un texte
</text>
</svg>
Once you have saved this, drag it into a browser window and you should see some shapes. SVGs are very powerful and you can attach code to their structure, making them interactive. If you want to learn more about how make SVGs take a look at w3schools |
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Exercise: Vector Graphics What is a drawing list Answer:
a set of commands used to define a vector image
Give some objects that can be used in vector graphics: Answer:
Give the properties needed to display a rectangle: Answer:
Give the properties needed to display a line: Answer:
Give the definition of a vector image: Answer: images defined using mathematics and geometry such as points, lines, curves, and shapes or polygon(s). Allowing for scalability Write a drawing list to create the following image:  Answer: <rect
width="1" height="1"
x="2" y="1"
fill="white" <!--optional you can leave this out-->
stroke="black"
stroke-width=1 /> <!--another small value will do-->
<rect
width="1" height="1"
x="11" y="0"
fill="white" <!--optional you can leave this out-->
stroke="black"
stroke-width=1 />
<rect
width="10" height="4"
x="2" y="6"
fill="black"
stroke="red"
stroke-width=5 /> <!--another small value will do-->
<circle
cx="7" cy="5"
r="2"
fill="blue" />
What would the following drawing list produce: <line
x1="0" y1="0"
x2="6" y2="6"
stroke="red" />
<rect
width="4" height="4"
x="1" y="1"
fill="yellow"
stroke="green"
stroke-width=1 />
<line
x1="6" y1="0"
x2="0" y2="6"
stroke="black" />
Answer:
In the above code, name the objects involved Answer: rect and line In the above code, list 4 different properties Answer:
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