/usr/share/doc/netCDF/html/dap4.html is in netcdf-doc 1:4.6.0-2build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 | <!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/xhtml;charset=UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=9"/>
<meta name="generator" content="Doxygen 1.8.13"/>
<meta name="viewport" content="width=device-width, initial-scale=1"/>
<title>NetCDF: DAP4 Support</title>
<link href="tabs.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript" src="dynsections.js"></script>
<link href="navtree.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="resize.js"></script>
<script type="text/javascript" src="navtreedata.js"></script>
<script type="text/javascript" src="navtree.js"></script>
<script type="text/javascript">
$(document).ready(initResizable);
</script>
<link href="search/search.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="search/searchdata.js"></script>
<script type="text/javascript" src="search/search.js"></script>
<link href="doxygen.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div id="top"><!-- do not remove this div, it is closed by doxygen! -->
<div id="titlearea">
<table cellspacing="0" cellpadding="0">
<tbody>
<tr style="height: 56px;">
<td id="projectlogo"><img alt="Logo" src="netcdf-50x50.png"/></td>
<td id="projectalign" style="padding-left: 0.5em;">
<div id="projectname">NetCDF
 <span id="projectnumber">4.6.0</span>
</div>
</td>
</tr>
</tbody>
</table>
</div>
<!-- end header part -->
<!-- Generated by Doxygen 1.8.13 -->
<script type="text/javascript">
var searchBox = new SearchBox("searchBox", "search",false,'Search');
</script>
<script type="text/javascript" src="menudata.js"></script>
<script type="text/javascript" src="menu.js"></script>
<script type="text/javascript">
$(function() {
initMenu('',true,false,'search.php','Search');
$(document).ready(function() { init_search(); });
});
</script>
<div id="main-nav"></div>
</div><!-- top -->
<div id="side-nav" class="ui-resizable side-nav-resizable">
<div id="nav-tree">
<div id="nav-tree-contents">
<div id="nav-sync" class="sync"></div>
</div>
</div>
<div id="splitbar" style="-moz-user-select:none;"
class="ui-resizable-handle">
</div>
</div>
<script type="text/javascript">
$(document).ready(function(){initNavTree('dap4.html','');});
</script>
<div id="doc-content">
<!-- window showing the filter options -->
<div id="MSearchSelectWindow"
onmouseover="return searchBox.OnSearchSelectShow()"
onmouseout="return searchBox.OnSearchSelectHide()"
onkeydown="return searchBox.OnSearchSelectKey(event)">
</div>
<!-- iframe showing the search results (closed by default) -->
<div id="MSearchResultsWindow">
<iframe src="javascript:void(0)" frameborder="0"
name="MSearchResults" id="MSearchResults">
</iframe>
</div>
<div class="header">
<div class="headertitle">
<div class="title">DAP4 Support </div> </div>
</div><!--header-->
<div class="contents">
<div class="toc"><h3>Table of Contents</h3>
<ul><li class="level1"><a href="#dap4_accessing">The DAP4 Prototocol</a><ul><li class="level2"><a href="#dap4_introduction">DAP4 Introduction</a></li>
<li class="level2"><a href="#dap4_access">Accessing Data Using the DAP4 Prototocol</a></li>
<li class="level2"><a href="#dap4_defined_params">Defined Client Parameters</a></li>
<li class="level2"><a href="#dap4_debug">Notes on Debugging DAP4 Access</a></li>
</ul>
</li>
</ul>
</div>
<div class="textblock"><h1><a class="anchor" id="dap4_accessing"></a>
The DAP4 Prototocol</h1>
<h2><a class="anchor" id="dap4_introduction"></a>
DAP4 Introduction</h2>
<p>Beginning with netCDF version 4.2.2, optional support is provided for accessing data through DAP4 servers using the DAP4 protocol.</p>
<p>DAP4 support is automatically enabled if a usable curl library can be set using the LDFLAGS environment variable (similar to the way that the HDF5 libraries are referenced). DAP2 plus DAP4 support can forcibly be enabled or disabled using the –enable-dap flag or the –disable-dap flag, respectively. If enabled, then DAP4 support requires access to the curl library. Refer to the installation manual for details</p>
<p>DAP4 uses a data model that is similar to, but not identical with, the netCDF-Enhanced (aka netcdf-4) model. Generically, the DAP4 data model is encoded in XML document called a DMR. For detailed information about the DAP4 DMR, refer to the DAP4 specification Volume 1: <a href="http://docs.opendap.org/index.php/DAP4:_Specification_Volume_1">http://docs.opendap.org/index.php/DAP4:_Specification_Volume_1</a></p>
<h2><a class="anchor" id="dap4_access"></a>
Accessing Data Using the DAP4 Prototocol</h2>
<p>In order to access a DAP4 data source through the netCDF API, the file name normally used is replaced with a URL with a specific format. The URL is composed of three parts.</p><ul>
<li><p class="startli">URL - this is a standard form URL with specific markers to indicate that it refers to a DAP4 encoded dataset. The markers can be one of the following examples.</p><ul>
<li>[dap4]<a href="http://remotetest.unidata.ucar.edu/d4ts/test.01">http://remotetest.unidata.ucar.edu/d4ts/test.01</a></li>
<li>[protocol=dap4]<a href="http://remotetest.unidata.ucar.edu/d4ts/test.01">http://remotetest.unidata.ucar.edu/d4ts/test.01</a></li>
<li><a href="http://remotetest.unidata.ucar.edu/d4ts/test.01#dap4">http://remotetest.unidata.ucar.edu/d4ts/test.01#dap4</a></li>
<li><a href="http://remotetest.unidata.ucar.edu/d4ts/test.01#protocol=dap4">http://remotetest.unidata.ucar.edu/d4ts/test.01#protocol=dap4</a></li>
<li>dap4://remotetest.unidata.ucar.edu/d4ts/test.01</li>
</ul>
<p class="startli">Note that the last case is converted internally to one of the other forms.</p>
</li>
<li>Constraints - these are suffixed to the URL and take the form “?dap4.ce=<expression>”. The form of the constraint expression is somewhat complicated, and the specification should be consulted.</li>
<li>Client parameters - these may be specified in either of two ways. The older, deprecated form prefixes text to the front of the url and is of the the general form [<name>] or [<name>=value]. Examples include [show=fetch]. The newer, preferred form prefixes the parameters to the end of the url using the semi-standard '#' format: e.g. <a href="http://....#show=fetch&noprefetch">http://....#show=fetch&noprefetch</a>.</li>
</ul>
<p>It is possible to see what the translation does to a particular DAP4 data source in two steps. First, one can examine the DMR source through a web browser and then second, one can examine the translation using the "ncdump -h" command to see the corresponding netCDF-4 representation.</p>
<p>For example, if a web browser is given the following (fictional) URL, it will return the DMR for the specified dataset </p><div class="fragment"><div class="line">http:<span class="comment">//remotetest.unidata.ucar.edu/d4ts/test.01.dmr#dap4</span></div></div><!-- fragment --><p>By using the following ncdump command, it is possible to see the equivalent netCDF-4 translation.</p>
<div class="fragment"><div class="line">ncdump -h http:<span class="comment">//remotetest.unidata.ucar.edu/d4ts/test.01#dap4</span></div></div><!-- fragment --><h2><a class="anchor" id="dap4_defined_params"></a>
Defined Client Parameters</h2>
<p>Currently, a limited set of client parameters is recognized. Parameters not listed here are ignored, but no error is signalled.</p>
<p>Parameter Name Legal Values Semantics</p><ul>
<li>"log" | "log=<file>" - Turn on logging and send the log output to the specified file. If no file is specified, then output is sent to standard error.</li>
<li>"show=fetch" - This parameter causes the netCDF code to log a copy of the complete url for every HTTP get request. If logging is enabled, then this can be helpful in checking to see the access behavior of the netCDF code.</li>
</ul>
<h2><a class="anchor" id="dap4_debug"></a>
Notes on Debugging DAP4 Access</h2>
<p>The DAP4 support has a logging facility. Note that this is currently separate from the existing netCDF logging facility. Turning on this logging can sometimes give important information. Logging can be enabled by using the client parameter "log" or "log=filename", where the first case will send log output to standard error and the second will send log output to the specified file.</p>
<p>Users should also be aware that if one is accessing data over an NFS mount, one may see some .nfsxxxxx files; those can be ignored. </p>
</div></div><!-- contents -->
</div><!-- doc-content -->
<hr size="2"/>
<address style="text-align: center;">
<a href="http://www.unidata.ucar.edu/software/netcdf/">Return to the Main Unidata NetCDF page.</a><br>
<img src="unidata_logo_cmyk.png">
<address style="text-align: right;"><small>
Generated on Fri Feb 9 2018 19:21:24 for NetCDF. NetCDF is
a <a href="http://www.unidata.ucar.edu/">Unidata</a> library.</small></address>
</body>
</html>
|