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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /><title>Chapter 3. PHPlot Concepts</title><link rel="stylesheet" type="text/css" href="phplotdoc.css" /><meta name="generator" content="DocBook XSL Stylesheets V1.78.1" /><link rel="home" href="index.html" title="PHPlot Reference Manual" /><link rel="up" href="part1.html" title="Part I. PHPlot Programming" /><link rel="prev" href="starting-next.html" title="2.7. What's Next?" /><link rel="next" href="conc-overview.html" title="3.2. Programming Overview" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 3. PHPlot Concepts</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="starting-next.html">Prev</a> </td><th width="60%" align="center">Part I. PHPlot Programming</th><td width="20%" align="right"> <a accesskey="n" href="conc-overview.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="concepts"></a>Chapter 3. PHPlot Concepts</h2></div></div></div><div class="abstract"><p class="title"><strong></strong></p><p>
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This chapter explains the operation and use of PHPlot.
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For advanced topics, see <a class="xref" href="advanced.html" title="Chapter 4. PHPlot Advanced Topics">Chapter 4, <em>PHPlot Advanced Topics</em></a>.
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</p></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="conc-defs"></a>3.1. Definitions</h2></div></div></div><div class="abstract"><p class="title"><strong></strong></p><p>
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This section contains definitions of terms used throughout the PHPlot
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Reference Manual.
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</p></div><p>
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</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><a id="def-alpha"></a>Alpha value</span></dt><dd><p>
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A component in a color system which represents the amount of transparency,
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or opacity. At one extreme, an alpha value indicates an opaque object
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which covers or hides whatever was drawn before it. At the other extreme,
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it indicates a completely transparent object which has no affect on
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whatever was drawn before it.
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</p></dd><dt><span class="term"><a id="def-dataset"></a>Data Set</span></dt><dd><p>
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A set of data points which represent some function, trend, samples, etc.
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</p></dd><dt><span class="term"><a id="def-devcoor"></a>Device Coordinates</span></dt><dd><p>
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The coordinate space used by GD to create images. The origin is at the
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upper left corner, X increases to the right, Y increases down, and the units
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are pixels. Also known as Pixel Coordinates or GD Coordinates.
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</p></dd><dt><span class="term"><a id="def-element"></a>Element</span></dt><dd><p>
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A component of a graph, such as a label, tick mark, axis, or plot.
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</p></dd><dt><span class="term"><a id="def-gd"></a>GD</span></dt><dd><p>
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A programming library used to create and manipulate images.
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GD can be found at the <a class="ulink" href="http://libgd.org/" target="_top">GD Graphics
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Library home page</a>, but is also included with PHP releases.
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You can think of GD as a software implementation of a video card.
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GD is also available via a PHP extension, and that is what PHPlot uses to
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create images.
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</p></dd><dt><span class="term"><a id="def-graph"></a>Graph</span></dt><dd><p>
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A complete, labeled, graphical representation of some data sets.
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In PHPlot, a graph contains a single plot and other elements such as axes,
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tick marks, and labels.
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</p></dd><dt><span class="term"><a id="def-horizplot"></a>Horizontal Plot</span></dt><dd><p>
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A plot in which the Y (vertical) axis represents the independent variable, and
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the X (horizontal) axis represents the dependent variable values.
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In a horizontal bar chart, for example, the bars extend to the right from the
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Y axis. A horizontal plot might represent X = F(Y), for example.
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(Note: This usage is specific to PHPlot. An alternate approach, not
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used by PHPlot, is to swap the X and Y axis orientation to make horizontal
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plots.)
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</p></dd><dt><span class="term"><a id="def-image"></a>Image</span></dt><dd><p>
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A graphical image, represented as data. For example, a PNG file is an image
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in PNG format which is stored in a file. PHPlot creates images using the GD
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library. A PHPlot image contains one or more graphs (but usually only one).
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</p></dd><dt><span class="term"><a id="def-palette"></a>Palette Image</span></dt><dd><p>
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A color image file, or image in memory, in which each pixel value is an
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index into a color map which contains the actual color. Typically, the
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pixel value is 8 bits, limiting this type of image to 256 distinct colors.
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See also <a class="link" href="concepts.html#def-truecolor">Truecolor Image</a>.
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</p></dd><dt><span class="term"><a id="def-plot"></a>Plot</span></dt><dd><p>
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The graphical representation of one or more data sets.
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In PHPlot, each graph contains a single plot, but a plot
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can contain representation of multiple data sets (for example,
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you can have 3 line charts on a plot).
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</p><p>
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Less formally, the term 'plot' is often used for the overall output of
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PHPlot: an image with a complete graphical representation of data, with
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labels, legend, title, etc.
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</p></dd><dt><span class="term"><a id="def-relativecoor"></a>Relative Coordinates</span></dt><dd><p>
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A coordinate space in which the X and Y coordinates represent a fraction of
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the size of an object. The point (0,0) is defined as the upper left corner
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of the object, and (1,1) is the lower right corner. (Relative coordinate values
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are not restricted to the range 0 to 1, however.) So a point specification
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in relative coordinates to an object is independent of the size of the object.
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This coordinate system is used by <a class="xref" href="SetLegendPosition.html" title="SetLegendPosition"><span class="refentrytitle">SetLegendPosition</span></a>.
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</p></dd><dt><span class="term"><a id="def-truecolor"></a>Truecolor Image</span></dt><dd><p>
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A color image file, or image in memory, in which each pixel value has a
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complete representation of the color of that pixel. The pixels may use 24
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bits, with 8 bits each for red, blue, and green color components, or 32
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bits with an additional alpha component.
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See also <a class="link" href="concepts.html#def-palette">Palette Image</a>.
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</p></dd><dt><span class="term"><a id="def-vertplot"></a>Vertical Plot</span></dt><dd><p>
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A plot in which the X axis represents the independent variable, and the Y
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axis represents the dependent variable values. This is the usual orientation
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for plots, and might represent Y = F(X).
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Compare with <a class="link" href="concepts.html#def-horizplot">horizontal plot</a>.
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</p></dd><dt><span class="term"><a id="def-worldcoor"></a>World Coordinates</span></dt><dd><p>
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The coordinate space of the plotted data. This is the real world
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coordinate space, in the units of whatever the plotted data measures.
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The origin of the world coordinate space is the 0,0 point on the X and Y
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axes.
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The X coordinate increases to the right, and the Y coordinate increases upwards.
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Note that the Y direction of world coordinates is opposite that of device
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coordinates.
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(World coordinates are only defined for plots in an orthogonal X/Y
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coordinate space, so there are no world coordinates for pie charts.)
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</p></dd></dl></div><p>
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</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="starting-next.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="part1.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="conc-overview.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">2.7. What's Next? </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 3.2. Programming Overview</td></tr></table></div></body></html>
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