~jstys-z/helioviewer.org/client5

<?php
/**
 * Helioviewer Web Server
 *
 * PHP version 5
 *
 * @category Application
 * @package  Helioviewer
 * @author   Keith Hughitt <keith.hughitt@nasa.gov>
 * @license  http://www.mozilla.org/MPL/MPL-1.1.html Mozilla Public License 1.1
 * @link     http://launchpad.net/helioviewer.org
 *
 * TODO 06/28/2011
 *  = Reuse database connection for statistics and other methods that need it? * 
 * 
 * TODO 01/28/2010
 *  = Document getDataSources, getJP2Header, and getClosestImage methods.
 *  = Explain use of sourceId for faster querying.
 *
 * TODO 01/27/2010
 *  = Add method to WebClient to print config file (e.g. for stand-alone
 *    web-client install to connect with)
 *  = Add getPlugins method to JHelioviewer module (empty function for now)
 */
require_once "src/Config.php";
require_once "src/Helper/ErrorHandler.php";

$config = new Config("../settings/Config.ini");
date_default_timezone_set('UTC');
register_shutdown_function('shutdownFunction');

if (isset($_REQUEST['action'])) {
    if ($_SERVER['REQUEST_METHOD'] == 'GET') {
        $params = $_GET;
    } else {
        $params = $_POST;
    }
}

if (!(isset($params) && loadModule($params))) {
    printAPIDocumentation();
}

/**
 * Loads the required module based on the action specified and run the
 * action.
 *
 * @param array $params API Request parameters
 *
 * @return bool Returns true if the action specified is valid and was
 *              successfully run.
 */
function loadModule($params)
{
    $valid_actions = array(
        "downloadScreenshot"   => "WebClient",
        "getClosestImage"      => "WebClient",
        "getDataSources"       => "WebClient",
        "getJP2Header"         => "WebClient",
        "getNewsFeed"          => "WebClient",
        "getTile"              => "WebClient",
        "getUsageStatistics"   => "WebClient",
        "shortenURL"           => "WebClient",
        "takeScreenshot"       => "WebClient",
        "getJP2Image"          => "JHelioviewer",
        "getJPX"               => "JHelioviewer",
        "launchJHelioviewer"   => "JHelioviewer",
        "buildMovie"           => "Movies",
        "downloadMovie"        => "Movies",
        "getMovieStatus"       => "Movies",
        "playMovie"            => "Movies",
        "queueMovie"           => "Movies",
        "uploadMovieToYouTube" => "Movies",
        "checkYouTubeAuth"     => "Movies",
        "getYouTubeAuth"       => "Movies",
        "getUserVideos"        => "Movies"
        //"getEventFRMs"           => "SolarEvents",
        //"getEvents"              => "SolarEvents"
    );
    
    include_once "src/Validation/InputValidator.php";

    try {
        if (!array_key_exists($params["action"], $valid_actions)) {
            $url = "http://" . $_SERVER["SERVER_NAME"] . $_SERVER["PHP_SELF"];
            throw new Exception(
                "Invalid action specified. See the <a href='$url'>" .
                "API Documentation</a> for a list of valid actions.", 26
            );
        } else {
        	// Execute action
            $moduleName = $valid_actions[$params["action"]];
            $className  = "Module_" . $moduleName;

            include_once "src/Module/$moduleName.php";

            $module = new $className($params);
            $module->execute();
            
            // Update usage stats
            $actions_to_keep_stats_for = array("getClosestImage", 
                "takeScreenshot", "getJPX", "uploadMovieToYouTube");
            
			// Note that in addition to the above, buildMovie requests and 
			// addition to getTile when the tile was already in the cache.
            if (HV_ENABLE_STATISTICS_COLLECTION && in_array($params["action"], $actions_to_keep_stats_for)) {
                include_once 'src/Database/Statistics.php';
                $statistics = new Database_Statistics();
                $statistics->log($params["action"]);
            }
        }
    } catch (Exception $e) {
        printHTMLErrorMsg($e->getMessage());
    }

    return true;
}

/**
 * Prints Helioviewer API documentation for each enabled module
 * 
 * @return void
 */
function printAPIDocumentation()
{
    $modules = array("WebClient", "JHelioviewer", "Movies");
?>
<!DOCTYPE html>
<html lang="en">
<head>
    <title>Helioviewer.org API</title>
    <link rel="shortcut icon" href="../favicon.ico">
    <meta http-equiv="X-UA-Compatible" content="chrome=1">
    <meta charset="utf-8" />
    <meta http-equiv="Cache-Control" content="No-Cache">
    <meta name="author" content="Keith Hughitt">
    <meta name="description" content="Helioviewer - Solar and heliospheric image visualization tool">
    <meta name="keywords" content="Helioviewer, hv, solar image viewer, sun, solar, heliosphere,
                                      solar physics, viewer, visualization, space, astronomy, API">
    <link rel="stylesheet" href="resources/css/api.css" />
</head>

<body>

<!-- Logo -->
<img alt="Helioviewer Logo" src="<?php echo HV_API_LOGO; ?>" style="float: left;">
<h1 style="position: relative; top: 22px;">API</h1>
<br />

<!-- Table of contents -->
<div class='toc'>
<ol>
    <li><a href="index.php#Overview">Overview</a></li>
<?php
    foreach($modules as $moduleName) {
        include_once "src/Module/$moduleName.php";
        call_user_func("Module_$moduleName" . '::printDocHeader');
    }
?>
    <li>
        <a href="index.php#Appendices">Appendices</a>
        <ol style="list-style-type: upper-latin;">
            <li><a href="index.php#Identifiers">Identifiers</a></li>
            <li><a href="index.php#VariableTypes"> Variable Types </a></li>
            <li><a href="index.php#Coordinates">Coordinates</a>
                <ul>
                    <li style='list-style-type: circle;'><a href="index.php#ArcsecondCoordinates">Arcseconds</a>
                    <li style='list-style-type: circle;'><a href="index.php#PixelCoordinates">Pixels</a>
                    <li style='list-style-type: circle;'><a href="index.php#ImageScale">Image Scale</a>
                </ul>
            </li>
        </ol>
    </li>
</ol>
</div>

<br />
<hr>
<br />

<!-- Main Content -->
<div class='content'>

    <!-- Overview -->
    <div id="Overview">
    
        <h1>Overview</h1>
        <p>In order to facilitate third-party application developers who wish to use content from and interact with
        Helioviewer.org, a number of <abbr title="Application Programming Interface">APIs</abbr> have been developed,
        offering  access to a variety of components used by Helioviewer. The simplest API actions require only a 
        single request and result in some resource being returned, e.g. a movie or <abbr title="JPEG 2000">JP2</abbr> 
        image series, or some action being performed, e.g. loading a particular image into Helioviewer.org. Some 
        API methods are more complex and involve multiple steps. For example, when creating a movie, the request is 
        first queued using one request. Subsequent requests are then used to determine when the movie has been built, 
        and then finally to download or play the movie.
        <br />
        <br />
    
        The general structure of queries is as follows:</p>
    
        <div class="summary-box">
            <?php echo HV_API_ROOT_URL;?>?action=methodName&amp;param1=value1&amp;param2=value2...
        </div>
    
        <p>The base URL is the same for each of the API methods (<a href="<?php echo HV_API_ROOT_URL;?>;"><?php echo HV_API_ROOT_URL;?></a>).
        The "action" parameter is required for all requests and specifies the specific functionality to access. In addition, other parameters
        may also be required depending on the specific API being accessed. The one exception to this rule is for
        <a href="index.php#CustomURLs">launching Helioviewer.org</a> with custom settings which is accessed from
        <a href="http://www.helioviewer.org/index.php"> http://www.helioviewer.org/index.php</a> and does not require an
        "action" to be specified. Finally, the queries may be sent using either a GET or POST request. In both cases the
        result is a <abbr name="JSON" title="JavaScript Object Notation">JSON</abbr> object
    
    </div>
<?php
    foreach($modules as $moduleName) {
        call_user_func("Module_$moduleName" . '::printDoc');
    }
    printDocumentationAppendices();
?>
</div>

<div style="font-size: 0.85em; text-align: center; margin-top: 20px;">
    Last Updated: 2012-02-22 | <a href="mailto:<?php echo HV_CONTACT_EMAIL; ?>">Questions?</a>
</div>

</body>
</html>
<?php
}

/**
 * Displays documentation appendices
 */
function printDocumentationAppendices()
{
?>
<!-- Appendices -->
    <div id="Appendices">
    <h1>Appendices:</h1>
    <p></p>
    <ol style="list-style-type: upper-latin;">
        <!-- Appendix A: Identifiers -->
        <li>
        <div id="Identifiers">Supported Identifiers <p>This appendice contains a list of the identifiers supported
        by Helioviewer. For some queries, complex identifiers may be built up from the simpler ones below. For example,
        to uniquely identify a specific type of image, you must specify a comma-separated set of four identifiers:
        Observatory, Instrument, Detector, and Measurement. For example, to refer to an EIT 171 image, the identifier
        <i>SOHO,EIT,EIT,171</i> is used.</p>

        <div class="summary-box" style="background-color: #E3EFFF;"><!-- Observatories -->
        <i>Observatories:</i><br />
        <br />
        <table class="param-list" cellspacing="10">
            <tr>
                <td width="140px"><strong>Identifier:</strong></td>
                <td><strong>Description:</strong></td>
            </tr>
            <tr>
                <td>SDO</td>
                <td>SDO (Solar Dynamics Observatory)</td>
            </tr>
            <tr>
                <td>SOHO</td>
                <td>SOHO (Solar and Heliospheric Observatory)</td>
            </tr>
            <tr>
                <td>STEREO_A</td>
                <td>STEREO_A (Solar Terrestrial Relations Observatory Ahead)</td>
            </tr>
            <tr>
                <td>STEREO_B</td>
                <td>STEREO_B (Solar Terrestrial Relations Observatory Behind)</td>
            </tr>
        </table>

        <br />

        <!-- Instruments -->
        <i>Instruments:</i><br />
        <br />
        <table class="param-list" cellspacing="10">
            <tr>
                <td width="140px"><strong>Identifier:</strong></td>
                <td><strong>Description:</strong></td>
            </tr>
            <tr>
                <td>AIA</td>
                <td>AIA (Atmospheric Imaging Assembly)</td>
            </tr>
            <tr>
                <td>EIT</td>
                <td>EIT (Extreme ultraviolet Imaging Telescope)</td>
            </tr>
            <tr>
                <td>HMI</td>
                <td>HMI (Helioseismic and Magnetic Imager)</td>
            </tr>
            <tr>
                <td>LASCO</td>
                <td>LASCO (Large Angle and Spectrometric Coronagraph Experiment)</td>
            </tr>
            <tr>
                <td>MDI</td>
                <td>MDI (The Michelson Doppler Imager)</td>
            </tr>
            <tr>
                <td>SECCHI</td>
                <td>SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation)</td>
            </tr>
        </table>

        <br />

        <!-- Detectors -->
        <i>Detectors:</i><br />
        <br />
        <table class="param-list" cellspacing="10">
            <tr>
                <td width="140px"><strong>Identifier:</strong></td>
                <td><strong>Description:</strong></td>
            </tr>
            <tr>
                <td>AIA</td>
                <td>AIA (Atmospheric Imaging Assembly)</td>
            </tr>
            <tr>
                <td>C2</td>
                <td>LASCO C2</td>
            </tr>
            <tr>
                <td>C3</td>
                <td>LASCO C3</td>
            </tr>
            <tr>
                <td>COR1</td>
                <td>Coronagraph 1</td>
            </tr>
            <tr>
                <td>COR2</td>
                <td>Coronagraph 2</td>
            </tr>
            <tr>
                <td>EIT</td>
                <td>EIT (Extreme ultraviolet Imaging Telescope)</td>
            </tr>
            <tr>
                <td>EUVI</td>
                <td>EUVI (Extreme ultraviolet Imager)</td>
            </tr>
            <tr>
                <td>HMI</td>
                <td>HMI (Helioseismic and Magnetic Imager)</td>
            </tr>
            <tr>
                <td>MDI</td>
                <td>MDI (The Michelson Doppler Imager)</td>
            </tr>
        </table>

        <br />

        <!-- Measurements -->
        <i>Measurements:</i><br />
        <br />
        <table class="param-list" cellspacing="10">
            <tr>
                <td width="140px"><strong>Identifier:</strong></td>
                <td><strong>Description:</strong></td>
            </tr>
            <tr>
                <td>94</td>
                <td>94 Ångström</td>
            </tr>
            <tr>
                <td>131</td>
                <td>131 Ångström</td>
            </tr>
            <tr>
                <td>171</td>
                <td>171 Ångström</td>
            </tr>
            <tr>
                <td>193</td>
                <td>193 Ångström</td>
            </tr>
            <tr>
                <td>195</td>
                <td>195 Ångström</td>
            </tr>
            <tr>
                <td>211</td>
                <td>211 Ångström</td>
            </tr>
            <tr>
                <td>284</td>
                <td>284 Ångström</td>
            </tr>
            <tr>
                <td>304</td>
                <td>304 Ångström</td>
            </tr>
            <tr>
                <td>335</td>
                <td>335 Ångström</td>
            </tr>
            <tr>
                <td>1600</td>
                <td>1600 Ångström</td>
            </tr>
            <tr>
                <td>1700</td>
                <td>1700 Ångström</td>
            </tr>
            <tr>
                <td>4500</td>
                <td>4500 Ångström</td>
            </tr>
            <tr>
                <td>white-light</td>
                <td>White-light</td>
            </tr>
            <tr>
                <td>continuum</td>
                <td>Intensity spectrogram</td>
            </tr>
            <tr>
                <td>magnetogram</td>
                <td>Magnetogram</td>
            </tr>
        </table>

        <br />

        </div>
        </div>
        </li>

        <br />

        <!-- Appendix B: Variable Types -->
        <li>
        <div id="VariableTypes">Variable Types
        <p>This appendice contains a list of some of the variable types
        used by the Helioviewer API's.</p>
        <div class="summary-box" style="background-color: #E3EFFF;">
        <br />
        <table class="param-list" cellspacing="10">
            <tbody valign="top">
                <tr>
                    <td width="25%"><strong>Type:</strong></td>
                    <td width="45%"><strong>Description:</strong></td>
                    <td><strong>Example:</strong></td>
                </tr>
                <tr>
                    <td>Boolean</td>
                    <td>A boolean value.</td>
                    <td>true</td>
                </tr>
                <tr>
                    <td>Integer</td>
                    <td>An integer.</td>
                    <td>12</td>
                </tr>
                <tr>
                    <td>Float</td>
                    <td>A floating point number.</td>
                    <td>2.4</td>
                </tr>
                <tr>
                    <td>String</td>
                    <td>A string.</td>
                    <td>SOHO</td>
                </tr>
                <tr>
                    <td>List</td>
                    <td>A comma-separated list of some other type, usually strings or integers</td>
                    <td>item1, item2</td>
                </tr>
                <tr>
                    <td>2d List</td>
                    <td>This is similar to a list except that each item of the list is a bracket-delineated list
                    itself.</td>
                    <td>[SOHO,EIT,EIT,171,1,100],[SOHO,LASCO,C2,white-light,0,100],[SOHO,MDI,MDI,continuum,1,50]</td>
                </tr>
                <tr>
                    <td>ISO 8601 UTC Date</td>
                    <td>ISO 8601 is a widely supported standarized date format.
                    (See <a href="#variable-type-resources">[1]</a>, <a href="#variable-type-resources">[2]</a>)</td>
                    <td>2003-10-05T00:00:00.000Z <span style="color: grey">// Milliseconds are optional but trailing "Z" should always included.</span></td>
                </tr>
            </tbody>
        </table>

        <br />
        <br />
        <div id="variable-type-resources"><strong>References:</strong><br />
        <br />
        [1] <a href="http://en.wikipedia.org/wiki/ISO_8601">ISO 8601 - Wikipedia</a><br />
        [2] <a href="http://www.w3.org/TR/NOTE-datetime">Date and Time Formats - W3.org</a><br />
        <br />
        </div>
        </div>
        </div>
        </li>
        <br />

        <!-- Appendix C: Working with Coordinates -->
        <li>
        <div id="Coordinates">Working with Coordinates in Helioviewer.org
            
        <h3>Overview</h3>

        <p>Several of the API methods supported by Helioviewer.org require you 
           to specify a rectangular region of interest or "ROI", which is simply
           the portion of the image or movie you are interested in.</p>
           
           There are two different methods for specifying region of interest 
           (ROI) in Helioivewer.org API requests. The first method is to
           specify the coordinates for the top-left and bottom-right corners of 
           the ROI in <a href="http://en.wikipedia.org/wiki/Minute_of_arc#Symbols.2C_abbreviations_and_subdivisions">arcseconds</a>. 
           The other option is to specify the position of the center of your 
           ROI in arcseconds and the dimensions for the ROI in pixels. In 
           either case you will also need to specify an image scale in 
           arcseconds per pixel.
           
           This appendix provides a description of how each of these methods
           can be used in API requests, and how to determine the appropriate
           arcsecond values to use to reach a desired effect.
           
        <h3 id="#ArcsecondCoordinates">Arcseconds</h3>
           
       <p>The first method for specifying an ROI in a Helioviewer.org API
          request is to specify the coordinates for the top-left (x1, y1) and
          bottom-right (x2, y2) corners of the ROI in arcseconds, with the 
          origin at the center of the Sun. The below image depicts the location 
          of the origin, and the direction of the axes, for this style 
          request.</p>
        
        <div style='width: 100%; text-align: center;'>
            <img src='resources/images/Helioviewer_ROI_Arcseconds_Overview.png' src='Helioviewer.org Coordinates Example Diagram (Arcseconds)' style='margin-left: auto; margin-right: auto;'/>
        </div>
        
        <p>To makes things more clear, below are some example requests, and the 
           <a href="#ImageScale">imageScale</a> and ROI corresponding with that 
           request.</p>
        
        <div class="summary-box" style="background-color: #E3EFFF;">
        <br />
        <span style='text-decoration: underline'>Examples:</span><br /><br />
        
        <b>1) A complete AIA image at 1/16 its natural resolution (zoomed out four times)</b>
        
        <p>In this case the desired image scale is 2^4 x (natural scale) = 16 x 0.6 = 9.6. Now to determine the ROI coordinates,
           we must first determine how large the image will be at the specified scale. AIA is normally 4096x4096, so at 1/16 its
           natural resolution it will be 256x256 pixels. Since the origin is in the middle of the Sun (which here is in the middle
           of the Sun), there top-left corner is 128 pixels up and to the left (-128, -128), and the bottom-right corner is 128 pixels down and
           to the right (128, 128). Since the ROI must be specified in arcseconds, and not in pixels, we multiply by the desired imageScale:
           128 x 9.6 = 1228.8.
           <br /><br />
           <i>URL:</i><a href="http://helioviewer.org/api/?action=takeScreenshot&date=2011-06-21T00:00:00.000Z&layers=[SDO,AIA,AIA,304,1,100]&imageScale=9.6&x1=-1228.8&y1=-1228.8&x2=1228.8&y2=1228.8&display=true">
               http://helioviewer.org/api/?action=takeScreenshot&date=2011-06-21T00:00:00.000Z&layers=[SDO,AIA,AIA,304,1,100]&imageScale=9.6&x1=-1228.8&y1=-1228.8&x2=1228.8&y2=1228.8&display=true
           </a>
           
        <br /><br />
        <b>2) The top-right quadrant of an EIT image at 200% magnification</b>
        
        <p>First, determine the desired image scale = 1 / 2^1 x (EIT native image scale) = 1/2 x 2.63 = 1.315. At this scale, the image which
           would normally be 1024x1024 pixels is now 2048x2048 pixels, and the coordinates for the ROI in pixels would is (0,-1024), (1024,0). To convert
           to arcseconds we multiple the pixel values by the arcsecond/pixel ratio (the imageScale) to get (0, -1346.56), (1346.56, 0).

           <br /><br />
           <i>URL:</i><a href="http://helioviewer.org/api/?action=takeScreenshot&date=2011-06-21T00:00:00.000Z&layers=[SOHO,EIT,EIT,171,1,100]&imageScale=1.315&x1=0&y1=-1346.56&x2=1346.56&y2=0&display=true">
               http://helioviewer.org/api/?action=takeScreenshot&date=2011-06-21T00:00:00.000Z&layers=[SOHO,EIT,EIT,171,1,100]&imageScale=1.315&x1=0&y1=-1346.56&x2=1346.56&y2=0&display=true
           </a>
        </p>
        </div>
        
        <p>Finally, don't forget that you can use Helioviewer.org to check the 
           coordinates and see if they are as you expect. Pressing the "m" key 
           will return the position of the mouse pointer in Helioviewer.org 
           viewport. Initially, the coordinates will be displayed in 
           arcseconds. Note, however, that the y-axis value displayed for 
           mouse-coordinates has the opposite sign to that passed in API 
           requests. This is because the mouse position is returned in a 
           coordinate system which is commonly used in solar physics. To get 
           around this you can simply flip the sign for the y-coordinate you 
           see on Helioviewer.org when mouse-coordinates are being displayed.
        </p>
        
        <h3 id="#PixelCoordinates">Pixels</h3>
        
        <p>
        Alternatively, if you prefer to explicityly specify the pixel dimensions for the image or movie,
        you can specify the center of your ROI in arc-seconds (x0, y0), relative to the center of the sun,
        and the width and height of the ROI in pixels. Although you are still required to work with Arcseconds
        for this method for some of the parameters, this provides a simple way to ensure that the resulting
        image or movie is a specific size in pixels.
        </p>
        
        <div style='width: 100%; text-align: center;'>
            <img src='resources/images/Helioviewer_ROI_Pixels_Overview.png' src='Helioviewer.org Coordinates Example Diagram (Pixels)' style='margin-left: auto; margin-right: auto;'/>
        </div>
        
        <p>
        Similar to the first method, you will also need to specify the <a href="#ImageScale">image scale</a> 
        to use, in arcseconds/pixel.
        </p>
        
        <div class="summary-box" style="background-color: #E3EFFF;">
        <br />
        <span style='text-decoration: underline'>Examples:</span><br /><br />
        
        <b>1) A complete EIT image at it's natural resolution</b>
        
        <p>According to the <a href="#ImageScaleTable">table of image scales</a> shown below, the native image scale for EIT is 2.63 arcseconds/pixel,
           and the image dimensions are 1024 x 1024 pixels.</p>
           <br /><br />
           <i>URL:</i><a href="http://helioviewer.org/api/?action=takeScreenshot&date=2011-07-07T00:00:00.000Z&layers=[SOHO,EIT,EIT,171,1,100]&imageScale=2.63&x0=0&y0=0&width=1024&height=1024&display=true">
               http://helioviewer.org/api/?action=takeScreenshot&date=2011-07-07T00:00:00.000Z&layers=[SOHO,EIT,EIT,171,1,100]&imageScale=2.63&x0=0&y0=0&width=1024&height=1024&display=true
           </a>
           
        <br /><br />
        <b>2) A 1024 x 768 sub-region centered at the top-right corner of an AIA 131 image, centered at the top-right quadrant, and
            the natural scale of AIA.</b>
        
        <p>Since we want to center the image in the top-right corner, we need to figure out what arcsecond coordinates correspond to the pixel
            coordinates (1024, -1024). At its native resolution, AIA images have an image scale of 0.6 arcseconds/pixel, so we multiple the pixel
            coordinates by this ratio to get the corresponding arcsecond values.</p>

           <br /><br />
           <i>URL:</i><a href="http://helioviewer.org/api/?action=takeScreenshot&date=2011-07-07T00:00:00.000Z&layers=[SDO,AIA,AIA,131,1,100]&imageScale=0.6&x0=614.4&y0=-614.4&width=1024&height=768&display=true">
               http://helioviewer.org/api/?action=takeScreenshot&date=2011-07-07T00:00:00.000Z&layers=[SDO,AIA,AIA,131,1,100]&imageScale=0.6&x0=614.4&y0=-614.4&width=1024&height=768&display=true
           </a>
        </div>
        
        <h3 id="#ImageScale">Image Scale</h3>
            <p>When working with coordinates in Helioviewer.org, it is also important to understand the spatial scale
               of the images you are viewing and requesting. Each type of image (AIA, LASCO, etc) shows the Sun at
               some spatial scale or resolution. That is, each image pixel represents a certain number of arcseconds, 
               and that ratio of arcseconds to pixels is refered to as the "image scale" for that image. Each of the
               different image types have their own native image scale, which is the number of arcseconds a pixel of
               the image represents when viewed at its native resolution.
               
               Below is a table listing the average native image scales and dimensions (in pixels) for images found on Helioviewer:
            </p>
               
            <div id="ImageScaleTable" class="summary-box" style="background-color: #E3EFFF;">
            <br />
            <table class="param-list" cellspacing="10">
                <tbody valign="top">
                    <tr>
                        <td width="40%"><strong>Image Type:</strong></td>
                        <td width="35%"><strong>Dimensions (pixels)</strong></td>
                        <td width="35%"><strong>Image Scale (arcseconds/pixel)</strong></td>
                    </tr>
                    <tr>
                        <td>AIA</td>
                        <td>4096 x 4096</td>
                        <td>0.6</td>
                    </tr>
                    <tr>
                        <td>COR-1</td>
                        <td>512 x 512</td>
                        <td>15.0</td>
                    </tr>
                    <tr>
                        <td>COR-2</td>
                        <td>2048 x 2048</td>
                        <td>14.7</td>
                    </tr>
                    <tr>
                        <td>EIT</td>
                        <td>1024 x 1024</td>
                        <td>2.63</td>
                    </tr>
                    <tr>
                        <td>HMI</td>
                        <td>4096 x 4096</td>
                        <td>0.6</td>
                    </tr>
                    <tr>
                        <td>LASCO C2</td>
                        <td>1024 x 1024</td>
                        <td>11.9</td>
                    </tr>
                    <tr>
                        <td>LASCO C3</td>
                        <td>1024 x 1024</td>
                        <td>56</td>
                    </tr>
                    <tr>
                        <td>MDI</td>
                        <td>1024 x 1024</td>
                        <td>1.985707</td>
                    </tr>
                </tbody>
            </table>
    
            <br />
            <strong>Note:</strong> The values listed above are average values. Often, the image scale and dimensions for a given
            type of image tends to stay the same over time, and as such you can often use the above values as-is. Occasionally, however,
            the scale or dimensions will vary. If you find that you are getting unexpected results, or would like a higher level of
            precision, you should first use the getClosestImage method to determine the exact dimensions and scale for the image you are
            requesting.
            </div>
    
            <p>The smaller the (native) image scale is, the more detail you can see. 
               For example, AIA has a much smaller native image scale (0.6"/px) than
               EIT does (2.63"/px) which is why you can see a lot more detail in AIA
               images.
            </p>
               
            <p>You are not limited to creating screenshots and movies at an image's native
               resolution, however, and so in an API request the imageScale specified
               need not (and in the case of composite images, often cannot) be the same
               as an images native resolution.
            </p>
               
            <p>For example, suppose you wanted to request an AIA image that is "zoomed out"
               by a factor of two. In this case, you would double the imageScale, so instead
               of 0.6, you would request an image scale of 1.2. Simiarly, when making a request
               which includes multiple layers, each of the layers will be scaled to match the
               imageScale you requested.
            </p>
        </div>
        </li>

        <!-- TODO : Appendice D: Image Layers -->
    </ol>
</div>
<?php 
}

/**
 * Displays a human-readable HTML error message to the user
 *
 * @param string $msg Error message to display to the user
 *
 * @return void
 */
function printHTMLErrorMsg($msg)
{
    ?>
<!DOCTYPE html>
<html lang="en">
<head>
    <?php
        $meta = "<!-- DATE: %s URL: http://%s%s -->\n";
        printf($meta, strftime('%Y-%m-%d %H:%m:%S'), $_SERVER['HTTP_HOST'], $_SERVER['REQUEST_URI']);
    ?>
    <title>Helioviewer.org API - Error</title>
</head>
<body>
    <div style='width: 50%; margin-left: auto; margin-right: auto; margin-top: 250px;
                text-align: center; font-size: 14px;'>
    <img src='<?php echo HV_API_LOGO; ?>' alt='Helioviewer logo'></img><br>
    <b>Error:</b> <?php echo $msg;?><br>
    </div>
</body>
</html>
    <?php
    exit();
}

/**
 * Shutdown function used to catch and log fatal PHP errors
 */
function shutDownFunction() { 
    $error = error_get_last();
    if ($error['type'] == 1) {
        handleError(sprintf("%s:%d - %s", $error['file'], $error['line'], $error['message']), $e->getCode());
    } 
}
?>