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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta name="GENERATOR" content="Mozilla/4.75 [en] (Windows NT 5.0; U) [Netscape]">
<title>FAQs</title>
</head>
<body text="#000000" bgcolor="#FFFFFF">
<table BORDER=0 CELLSPACING=5 CELLPADDING=5 WIDTH="100%" >
<tr>
<td WIDTH="180"><a href="http://www.cgns.org/"><img SRC="cgns.gif" ALT="CGNS logo" BORDER=0 height=111 width=180 align=CENTER></a></td>
<td ALIGN=CENTER>
<h1>
<font color="#000000">CFD General Notation System<br>
Frequently Asked Questions (FAQs)</font></h1>
</td>
</tr>
<tr>
<td COLSPAN="2">
<hr></td>
<td> </td>
</tr>
<tr>
<td ALIGN=LEFT VALIGN=TOP WIDTH="180">
<table BORDER CELLSPACING=0 CELLPADDING=5 WIDTH="100%" >
<tr>
<td VALIGN=TOP>
<p><b>CGNS site pages</b>
<br><a href="index.html">CGNS Home</a>
<br><a href="WhatIsCGNS.html">What is CGNS?</a>
<br><a href="starting.html">Getting Started</a>
<br><a href="news.html">Latest News</a>
<br><a href="hdf5.html">Switch to HDF5</a>
<br><a href="steering.html">Steering Committee</a>
<br><a href="Implementations.html">Implementations</a>
<br><a href="CGNStalk.html">Discussion Group</a>
<br><a href="download.html">Download</a>
<br><a href="Utilities.html">Contributed Utilities</a>
<br><a href="CGNSFiles.html">Example CGNS Files</a>
<br><a href="Proposals.html">Proposed Extensions</a>
<br><b><font color=red>FAQs</font></b>
<p><b>Documentation pages</b>
<br><a href="CGNS_docs_current/index.html">Documentation Home</a>
<br><a href="CGNS_docs_current/index.html#Papers">Papers and Slides</a>
<br><a href="CGNS_docs_current/index.html#Minutes">Meeting Minutes</a>
<br><a href="CGNS_docs_current/user/index.html">User's Guide</a>
<br><a href="CGNS_docs_current/overview/index.html">Overview</a>
<br><a href="CGNS_docs_current/sids/index.html">SIDS</a>
<br><a href="CGNS_docs_current/filemap/index.html">SIDS File Mapping</a>
<br><a href="CGNS_docs_current/midlevel/index.html">Mid-Level Library</a>
<br><a href="CGNS_docs_current/cgio/index.html">CGIO User's Guide</a>
</td>
</tr>
</table>
</td>
<td ALIGN=LEFT VALIGN=TOP>
<p><a href="#general">General Questions</a> are covered first, followed by
<a href="#installation">Installation Questions</a>.
<hr WIDTH="100%">
<a NAME="general"><h2>General Questions</h2>
<p> Q: <b>How do I obtain CGNS?</b> </p>
<p> A: CGNS is distributed via
<a href="https://github.com/CGNS">https://github.com/CGNS</a>.
(Old, stable releases will remain available on SourceForge until the
transition from SourceForge to GitHub is completed.)
All CGNS software is free, and
is governed by the license described at the bottom of the
<a href="WhatIsCGNS.html">What is CGNS?</a> page. You can
obtain the software by going to our <a href="download.html">Download</a> page.
<br>
<p> Q: <b>How can I get help if I run into problems?</b> </p>
<p> A: There is no full-time CGNS "help desk." Instead, the CGNS
community relies on both extensive documentation and other CGNS users for
help and support. The documentation is available at
<a href="CGNS_docs_current/index.html">Documentation Home</a>.
In particular, we recommend that beginning users consult the
<a href="CGNS_docs_current/user/index.html">User's Guide</a>,
which includes many example programs in both Fortran and C.
If you still need help, please make use of the
<a href="CGNStalk.html">Discussion Group</a>, via:
<a href="https://github.com/CGNS/CGNS/discussions">cgnstalk</a>. We
strongly encourage you to watch the CGNS/CGNS repository so you can be a part of ongoing
CGNS discussions and updates.
<br>
<p> Q: <b>There is a lot of documentation... which are most important for me
to read?</b> </p>
<p> A: We recommend the
<a href="CGNS_docs_current/user/index.html">User's Guide</a>
as a first "must read." This will introduce you to CGNS and guide you through
many basic examples.
As a tutorial overview, the "CGNS Tutorial Session" (slide format) may also be useful.
It can be found under
<a href="CGNS_docs_current/index.html#Papers">Papers and Slides</a>
(Slides section).
The full details about the intellectual content of
CGNS files are given in the
<a href="CGNS_docs_current/sids/index.html">SIDS</a> document
(which is also an AIAA Recommended Practice).
Finally, when you start programming, you will probably need to refer to the
<a href="CGNS_docs_current/midlevel/index.html">Mid-Level Library</a>
documentation, which describes the Fortran and C calls used to read and write
the CGNS files.
<br>
<p> Q: <b>What does SIDS mean?</b> </p>
<p> A: SIDS stands for "Standard Interface Data Structures." It defines
the details of how data is stored in a CGNS file. CGNS files themselves are
entities that are organized internally into a set of "nodes" in a tree-like structure.
The top-most node is referred to as the "root node," and each node has
an associated name, label, data, and (possible) children nodes. It is the SIDS
that tells you how those nodes are organized, and
what data is contained therein.
<br>
<p> Q: <b>What do I do if CGNS is not capable of handling my particular
application?</b> </p>
<p> A: CGNS has been designed to be very flexible, for handling a wide
range of flow physics applications. However, if you find an application
that is not covered, you are encouraged to utilize the "UserDefined"
construct as needed. In fact, the UserDefined node can be used to create
an entire tree consisting of multilpe levels of UserDefined children nodes,
so you can create an entire "pattern" for storing particular information.
Furthermore, if you feel that a change or addition is needed
to the SIDS, or if you feel that a particular "pattern" you have created
might be useful to others, please consider submitting a proposal for extension
(see <a href="Proposals.html">Proposed Extensions</a> page).
<br>
<p> Q: <b>When there are multiple ZONES associated with a given CGNS file, is there a
particular way that they should be named?
</b> </p>
<p> A:
It is important for CGNS users to know that
when a CGNS file is opened via the cg_open() MLL function, the zones are sorted
<i>alphanumerically</i> by name (the creation order is ignored/discarded). This mechanism is
provided to enable ordinal zone indexing. Therefore, if ordinal zone indexing is desired,
it is considered good standard
practice to always <u>choose zone names to
be alphabetically increasing.</u> For example, Zone0001, Zone0002, etc. is appropriate for up to
9999 zones.
(Important: Because the cgnsview tool uses the low-level cgio API, it does not sort the zones
by name and zone order presented may not match that of the MLL API. Generally, cgnsview
presents the zones in creation order for both ADF and HDF5 formats. One exception is CGNS files
that are either created or opened using the HDF5 v1.6 library (or older) will always be presented
alphabetically (creation order tracking was added to HDF5 in v1.8).)
<br>
<p> Q: <b>How do I view my CGNS files?</b> </p>
<p> A: CGNS files are most easily viewed using the tool "cgnsview"
(part of the cgnstools). This tool is
Tcl/Tk based. Cgnsview also has the capability to plot and to translate to/from
PLOT3D format, for example.
<br>
<p> Q: <b>How do I know if a CGNS file is correct according to the SIDS
definitions?</b> </p>
<p> A: There are currently tools being developed to evaluate how well a
file complies with the CGNS rules ("SIDS-compliance"). For example,
the utility "cgnsview" (available as part of the
cgnstools), has a capability called "check CGNS" that checks for compliance
to some degree (this tool can also be run independently of cgnsview).
There are still ongoing discussions about this subject.
For example, it is possible that different levels of compliance may be
defined in the future.
<br>
<p> Q: <b>What do the CGNS Version numbers mean, and does the CGNS library maintain
backward/forward compatibility?</b> </p>
<p> A: The CGNS versions are currently numbered as follows: "Version x.y, Revision z",
or "Version x.y-z". (However, the revision number is often left off, so you will typically
only see "Version x.y".) The first number represents the "major" version number. Within
this number, the library maintains forward compatibility. For example, Version 2.3 of the
library can read a Version 2.5 CGNS file, but Version 1.y cannot necessarily read any Version 2.y
(or later) file. A new "major" version number is assigned
either when forward compatibility is lost, or else when there is a significant
change made to the API. The second number is the "point release" number. It
increments when there are relatively minor changes to the API, or with the
addition of new features. The third number (the revision number) changes with
bug fixes. Major releases and point releases are announced (via
the <a href="news.html">Latest News</a> page and via
the CGNSTalk <a href="CGNStalk.html">Discussion Group</a>), whereas revisions are
generally not announced. Note that CGNS always maintains backward compatibility: the most recent
version of the library will be able to read all older versions CGNS files.
<br>
<p> Q: <b>How do I keep up with the goings-on of the Steering Committee?</b> </p>
<p> A: The CGNS Steering Committee meets and/or holds telecons about 5 times
per year. The minutes are posted on the
<a href="CGNS_docs_current/index.html#Minutes">Meeting Minutes</a>
page. Also, the meetings are an open forum: anyone is welcome to attend.
To find out the date and time of the next meeting, look in the most recent meeting minutes.
<br>
<p><a NAME="logoQ"></a> Q: <b>Can I use the CGNS logo as part of my website or other documentation?</b> </p>
<p> A: We encourage anyone to freely use the CGNS logo when distributing or documenting CGNS
related information. The logo adds prestige and credibility to web sites, publications,
displays, announcements, and activities. However, the use of the logo in such a way as
to imply approval, endorsement, or responsibility of the CGNS committee is prohibited
without written permission.</p>
<p> <a href="cgns_color.gif">Logo file (color) in .gif format (13 kB)</a>
<a href="cgns_bw.gif">Logo file (black & white) in .gif format (12 kB)</a>
<p> <a href="cgns_color.jpg">Logo file (color) in .jpg format (12 kB)</a>
<a href="cgns_bw.jpg">Logo file (black & white) in .jpg format (9 kB)</a>
<br>
<p> Q: <b>Is CGNS an ISO standard?</b> </p>
<p> A: Between 1999 and 2002, an effort was spearheaded by Boeing to establish an ISO-STEP standard for the
representation, storage, and exchange of digital data in fluid dynamics based on the CGNS standard.
Unfortunately, the effort had to be curtailed because of budget problems. It was subsequently decided that an
existing ISO standard on finite element solid mechanics would be rewritten and submitted to include CGNS
as well as an integrated engineering analysis framework.
Some details on this subsequent effort can be found in archives of the
<a href="CGNS_docs_current/index.html#Minutes">Meeting
and Telecon Minutes</a>.
This new ISO effort was being conducted completely outside of
the control of the CGNS committee. Therefore, the current status is not known.</p>
<hr WIDTH="100%">
<a NAME="installation"><h2>Installation Questions</h2>
<p> Q: <b>How to install CGNS on Windows from source with HDF5 also built from source using Microsoft C compiler?</b> </p>
<p> A: There are two components to consider: (1) Installation of HDF5 from source and
(2) Installation of CGNS using the HDF5 built in (1).
<h3>(1) Installation of HDF5 from source.</h3>
This guide is a quick start summary of the HDF5 build instruction
provided by <a
href="https://support.hdfgroup.org/HDF5/release/cmakebuild.html">The
HDF Group</a>. CGNS does not need the Fortran HDF5 APIs, so it is
not required to enable Fortran when building HDF5. CGNS also does
not use compression, so Zlib and SZIP can be disabled when building
HDF5. <u><br>
<br>
<b>Prerequisites</b></u><br>
<ol>
<li> CMake MUST be installed. The configuration scripts
require a minimum CMake version 3.2.2, the current version of
CMake is strongly encouraged.</li>
<li>(Optional, but strongly encouraged) <a
href="http://nsis.sourceforge.net/Main_Page">NSIS</a> or <a
href="http://wixtoolset.org/">WiX</a> should be installed to
create an install image with CPack. NSIS will create a .exe
installer. WiX will create a .msi installer. This guide assumes
WiX is installed.</li>
<li>Git for cloning the HDF5 and CGNS source.</li>
<li>Blank spaces <strong>MUST NOT</strong> be used in directory
path names as this will cause the build to fail.</li>
<li>Perl needs to be installed if building from source from the
repository. If building from released <a
href="https://www.hdfgroup.org/downloads/hdf5/source-code/#src">HDF5
source</a> then it is not needed.<br>
</li>
</ol>
<p><b><u>Installation<br>
</u></b></p>
<p>In a directory (Noting item #4 of the Prerequisites) download the
HDF5 source,<br>
</p>
<pre> git clone https://bitbucket.hdfgroup.org/scm/hdffv/hdf5.git<br></pre>
Copy three files in the HDF5 source directory <i>hdf5\config\cmake\scripts </i>to the current directory<i>.
<br></i><pre> copy hdf5\config\cmake\scripts\HDF5options.cmake .
<br> copy hdf5\config\cmake\scripts\CTestScript.cmake .
<br> copy hdf5\config\cmake\scripts\HDF5config.cmake .<br>
</pre>The only file that needs to be edited is HDF5options.cmake. Disable Zlib and Szip by setting the lines in HDF5options to,
<br><pre>### disable ext zlib building<br>set(ADD_BUILD_OPTIONS "${ADD_BUILD_OPTIONS} -DHDF5_ENABLE_Z_LIB_SUPPORT:BOOL=OFF")
<br>### disable ext szip building
set(ADD_BUILD_OPTIONS "${ADD_BUILD_OPTIONS} -DHDF5_ENABLE_SZIP_SUPPORT:BOOL=OFF")
set(ADD_BUILD_OPTIONS "${ADD_BUILD_OPTIONS} -DHDF5_ENABLE_SZIP_ENCODING:BOOL=OFF")
</pre>Create a batch script, <i>gen.bat</i>, to build HDF5. The contents will be,<br>
<pre> ctest -S HDF5config.cmake,BUILD_GENERATOR=VS201764,CTEST_SOURCE_NAME=hdf5,STATIC_ONLY=NO -C Release -VV -O hdf5.log</pre>
If you are using a different version of Visual Studio, then change <i>BUILD_GENERATOR=</i> to the matching one found in HDF5config.cmake in the section "Following describes compiler". <br>
<br>Execute <i>gen.bat</i>,<br>
<pre> gen.bat</pre>
Doing so will build and test the installation of HDF5. The HDF5 build directory will be called '<i>build</i>'. Change into the '<i>build</i>' directory and run cpack,<br>
</i><pre> cpack -C Release</pre>
Assuming WiX is installed, cpack will create an HDF5-X.X.X-win64.msi installer. Select the msi file and follow the installation GUI instructions, which will install HDF5.<br>
<h3>(2) Installation of CGNS from source.</h3>
Download CGNS source,<br>
<pre> git clone https://github.com/CGNS/CGNS.git</pre>
Create a directory which will contain the build of CGNS, don't build CGNS in the source directory.<br><br>mkdir build_cgns<br>cd build_cgns<br><br>Create a batch script which will be used to build CGNS with cmake, the contents will vary depending on the options you chose to build CGNS with, but a sample file, <a href="BuildingCGNS/build_cgns_MS.bat">build_cgns_MS.bat</a>, would be:
<br><pre>@echo OFF<br>:: Run the cmake command<br>cmake -G "Visual Studio 15 Win64"^<br> -D CMAKE_PREFIX_PATH:PATH="C:\Program Files\HDF_Group\HDF5\1.11.2\cmake" ^ <br> -D CMAKE_BUILD_TYPE=Release ^<br> -D CGNS_ENABLE_FORTRAN:BOOL=OFF ^<br> -D CGNS_BUILD_SHARED:BOOL=OFF ^<br> -D CMAKE_STATIC_LINKER_FLAGS:STRING="/NODEFAULTLIB:library" ^<br> -D CMAKE_EXE_LINKER_FLAGS:STRING="/NODEFAULTLIB:library" ^<br> -D CGNS_USE_SHARED:BOOL=OFF ^<br> -D CGNS_ENABLE_LEGACY=ON ^<br> -D CGNS_ENABLE_64BIT=BOOL=ON ^<br> -D CGNS_BUILD_CGNSTOOLS:BOOL=OFF ^<br> -D CGNS_ENABLE_TESTS:BOOL=ON ^<br> -D CMAKE_VERBOSE_MAKEFILE:BOOL=ON ^<br> -D CGNS_ENABLE_HDF5:BOOL=ON ^<br> -D CGNS_ENABLE_PARALLEL:BOOL=OFF ^<br> -D HDF5_BUILD_SHARED_LIBS:BOOL=OFF ^<br> -D HDF5_NEED_MPI:BOOL=OFF ^<br> -D HDF5_NEED_ZLIB:BOOL=OFF ^<br> -D HDF5_NEED_SZIP:BOOL=OFF ^<br> ../CGNS<br>cmake --build . <br></pre>
NOTES: <b>CMAKE_PREFIX_PATH</b> -- Set to where HDF5 was installed in Step (1).<br> <b>-G</b> -- Set to the correct Visual Studio edition.<br> ../CGNS -- This is the path to the CGNS source<br>
<br>To test the CGNS installation run <i>ctest</i>,
<br><pre> ctest .</pre> <br><br><br><br><br><br><br><br><br>
</p>
<!--<p>For information purposes, this lists some of the original documents from
the earlier 1999-2002 effort. <b>Note:</b> due to copyright restrictions these documents
are no longer provided here, and must be obtained directly from ISO.</p>
<blockquote>
<dir>
<li>
<b>Draft of the AP for fluid dynamics data</b></li>
<br>Application protocol: fluid dynamics data: Part_237_030731.pdf
<br>
<li>
<b>Committee draft of the mesh-based computational fluid dynamics - Part
1fd -</b></li>
<br>Part 1FD defines specialized components of the standard applicable
only to CFD. In the future, other 100-series parts will be produced with
specializations for flight test data, wind tunnel data, and other categories
of fluid dynamics data. These will all be components of AP237.
<p>Integrated resource: Mesh-based computational fluid dynamics
<br>Part_110_CD_030721.pdf</dir>
</blockquote>
<blockquote>
<dir>
<li>
<b>Committee draft of a resource to support the Fluid Dynamics AP - Part
53 -</b></li>
<br>General product data management information for numerical analysis
results. This document will be refereced from AP 237 and Part 1xx.
<p>Integrated resource: Numerical analysis
<br>Part_53_CD_030721.pdf
<br>
<li>
<b>Committee draft of the mesh-based topology resource - Part 52 -</b></li>
<br>Generic data structures for mesh-based data, both structured and unstructured
mesh. This document will be referenced from AP 237 and Part 1xx.
<p>Integrated resource: Mesh-based topology
<br>Part_52_CD_030721.pdf
</dir>
</blockquote>-->
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