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<?xml version="1.0" encoding="ISO-8859-1" standalone="no"?>
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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 2. Getting Started with PHPlot</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="install-next.html" title="1.3. Next Step" /><link rel="next" href="starting-create.html" title="2.2. Creating the Object" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 2. Getting Started with PHPlot</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="install-next.html">Prev</a> </td><th width="60%" align="center">Part I. PHPlot Programming</th><td width="20%" align="right"> <a accesskey="n" href="starting-create.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="starting"></a>Chapter 2. Getting Started with PHPlot</h2></div></div></div><div class="abstract"><p class="title"><strong></strong></p><p>
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This chapter will help you get started with PHPlot.
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</p><p>
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The material in this chapter was originally from the PHPlot Quick Start
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and Examples document, by Afan Ottenheimer and Miguel de Benito,
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distributed with PHPlot. It has undergone much editing and any mistakes
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are not their fault.
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</p></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="starting-intro"></a>2.1. Introduction</h2></div></div></div><p>
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Many web sites need to create real-time or dynamic charts and graphs from
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live data sets. Many users have found PHP a great way for this dynamic
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creation of images using the <a class="link" href="concepts.html#def-gd">GD</a> library.
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The advantage of using the server to create an image (that is, using a
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server-side scripting language rather than a client-side language such as
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Java) is that one does not have to worry about browser compatibility or
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client operating system compatibility issues.
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</p><p>
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PHPlot is a specialized graphics library which provides a means for your
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PHP-enabled web server to create and manipulate graphs as objects and
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display the completed graph as an image.
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PHPlot uses the GD library to create elementary shapes such as lines,
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rectangles, and text, but hides the details of GD from the application
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programmer.
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</p><p>
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Data sets are passed to PHPlot using PHP arrays, in a convenient format
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for database-driven sites.
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</p><p>
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First, lets discuss how PHPlot works in general with some terminology.
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(More complete definitions can be found in <a class="xref" href="concepts.html#conc-defs" title="3.1. Definitions">Section 3.1, “Definitions”</a>.)
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A PHPlot <span class="emphasis"><em>image</em></span> can consist of several
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<span class="emphasis"><em>graphs</em></span> (but usually has only one), each graph consisting
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of several <span class="emphasis"><em>elements</em></span> (like lines, axes, and labels).
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</p><p>
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To use PHPlot, you create a PHP object from the PHPlot class, for example:
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</p><pre class="programlisting">$plot = new PHPlot;
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</pre><p>
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Then you set the properties of the object, by using a series of function
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calls (actually methods of the class). These define the characteristics of
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the image, the graph or graphs, and their elements. This includes setting
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the array containing the data to be plotted, defining titles if you want
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them, and many optional elements and style settings. You can think of this
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as "drawing" elements into the image, but in fact PHPlot just notes your
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intentions and doesn't do much until you are finished.
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</p><p>
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When you are done describing a graph, you instruct PHPlot to "draw" the
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graph into the image. When you are done with all graphs in an image,
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you need to instruct PHPlot to "print" (output) the image.
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Since most images contain only one graph, PHPlot simplifies
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this process by default. Unless instructed otherwise, PHPlot will "print"
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the image (output it to the browser) as soon as you tell it to "draw"
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(render) the first graph.
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</p><p>
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Usually, PHPlot will "print" the image directly to the user's browser.
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The result will be a complete HTTP response with headers, so your PHP
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script must not produce any other output (except for optional headers).
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The user will be see the image either as a result of accessing your
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script directly with a URL, like
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<code class="literal">http://www.example.com/graphs/myplot.php</code>,
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or you can embed the image in a web page using an image tag, like this:
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</p><pre class="screen"><IMG SRC="http://www.example.com/graphs/myplot.php">
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</pre><p>
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</p><p>
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Instead of sending the image to the browser, your application can instead
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choose to write the PHPlot image to a file on the server. This could be
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useful if you want to implement server-side caching of image files.
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(PHPlot itself does not currently provide caching.)
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</p><p>
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Before continuing, we need to mention coordinates.
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PHPlot uses two coordinate spaces: one for the image, and one for the
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data you are plotting.
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<span class="emphasis"><em>World Coordinates</em></span>
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are the X,Y coordinates of your data, relative to the axis origin,
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in the units of the data sets.
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Your data array uses world coordinates, as do tick mark labels on the X and
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Y axis.
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<span class="emphasis"><em>Device Coordinates</em></span>
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measure pixels in the image according the the GD convention, with
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the origin in the upper left corner of the image. These are also
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called Pixel Coordinates.
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PHPlot tries to place elements on your graph appropriately, but if
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you need to override its choices you will use device coordinates to
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position the elements.
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</p><p>
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The rest of this chapter explains how to write a PHP script which creates
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a plot using PHPlot.
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Information on PHP can be found at
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<a class="ulink" href="http://www.php.net/" target="_top">www.php.net</a>.
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Information about the GD library which PHP uses to create images can
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be found at <a class="ulink" href="http://libgd.org/" target="_top">libgd.org</a>.
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More information about PHPlot can be found at
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<a class="ulink" href="http://phplot.sourceforge.net/" target="_top">phplot.sourceforge.net</a>.
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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="install-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="starting-create.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">1.3. Next Step </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 2.2. Creating the Object</td></tr></table></div></body></html>
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