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i NCSA HDF Vset
Introduction i
National Center for Supercomputing Applications
November 1990
Introduction
Overview
This introduction provides an overview of NCSA Hierarchical
Data Format (HDF) Vset capabilities on the Cray, Alliant, Sun,
Iris, Macintosh, and IBM PC. The organization and use of this
manual are described and notational conventions explained.
What Is an HDF Vset?
The HDF Vset is a new storage scheme that allows more than
raster images, palettes, scientific datasets and annotations to be
stored in the HDF file. It is a versatile storage scheme that
introduces two new and useful features.
1. Storage of multi-variate data fields
Applications may now define and store data from fields of
different types together within the HDF file and then access data
from all or some of the fields.
2. Hierarchical grouping of related datasets
Applications may explicitly link related datasets within the
HDF file to form logically-related groups called vsets.
The HDF Vset enables applications with the following capabilities
inherent to HDF: (1) a means of defining data fields and types (2)
a means of specifying data layout in the HDF file, and (3) greater
control over data access.
Uses of HDF Vsets
The HDF Vset is especially targeted towards applications that
manipulate mesh, polygonal, or any connectivity data. Among the
applications that could benefit by using this storage scheme are
finite-element analysis, surface modeling, and sparse matrices.
Using HDF Vset you can group simulation data for animation, as
well as store and view images with original data for more
meaningful data interpretation.
NCSA developers originally designed the HDF Vset to store
irregularly-gridded and multi-variate graphical and scientific
data, and to facilitate data exchange among the research
community. It has since evolved into a general and simple
interface for storing almost any large non-uniform datasets.
Consistent with existing HDF goals, vset data is self-describing
and portable. In addition, provision exists for attaching
annotations and textual descriptions.
New Features in HDF Vset 2.0
NCSA HDF Vset 2.0 offers several new features and
improvements including memory allocation, long integer support,
a new secondary name field, and multiple file access.
Memory Allocation
HDF Vset allocates memory for vgroups and vdatas dynamically.
Therefore, there is no upper limit on how many vgroups or vdatas
that may be accessed by an application.
Long Integer Support
HDF Vset now allows storage of long integers in a vdata. Integer
datasets greater than 65353 must be stored as long integers or they
will be truncated. Each long integer will be stored in 4 bytes within
a vdata.
The routine VSfdefine now recognizes the field type constant
LOCAL LONGTYPE. Use this constant to define a field to be of type
long. VSwrite expects data corresponding to that field to be stored
in a long array. Similarly, VSread expects to be passed a long
array into which long integers will be retrieved and returned.
New Secondary Name Field
Each vgroup or vdata now has a secondary name field. This field,
called the class field of the vgroup or vdata, is just another text field
like the vgname or vsname. Its purpose is to provide another key
with which that vgroup or vdata may be classified. It is analogous
to the file-extension in a filename, e.g., "DAT" in the filename
"TEST1.DAT". Usage of the class field is optional, and is
application-dependent.
The routines Vsetclass and VSsetclass set this class field for a
vgroup and a vdata, respectively. Similarly, the routines
Vgetclass and VSgetclass return the class fieldname of a
vgroup and a vdata, respectively.
Multiple File Access
HDF Vset now allows several HDF files to be opened for reading
and writing Vsets simultaneously. This feature only works when
the Vset library is used with release 3.1 or later of the base HDF
library. No new routines are needed.
Open as many files as needed using DFopen, and then use the file
pointers as usual in the Vset routines. Upon completion, each
opened file must be properly closed by a call to DFclose.
NOTE: Please see Appendix E, "Compatibility Information for 1.0
Users" for important compatibility information for release 1.0
users.
System Requirements
The HDF Vset library is available for any of the following
computer systems: Cray/UNICOS, SGI/UNIX, Sun/UNIX,
Alliant/CONCENTRIX, VAX/Ultrix, Vax/VMS,
Macintosh/MacOS, and IBM PC/MS-DOS.
Use of This Manual
This manual is designed for users whose applications access vsets
from HDF files.
.c3.Manual Contents
The manual is organized into the following chapters:
Chapter 1, "NCSA HDF Vset Basics," describes HDF Vsets and
gives simple examples on using it.
Chapter 2, "Vdatas," describes in detail the organization of data
within vdatas and techniques for manipulating the data.
Chapter 3, "Vset Utilities," describes in detail the utilities for
manipulating Vsets.
Chapter 4, "Vgroup Routine Descriptions," describes in detail the
routines that manipulate vgroups.
Chapter 5, "Vdata Routine Descriptions," describes in detail the
routines that manipulate vdatas.
Chapter 6, "HDF Vset FORTRAN Interface," describes Vset
calling sequences from FORTRAN.
Appendix A, "NCSA HDF Vset Calls at a Glance," allows quick
referencing of all present Vset Calls.
Appendix B, "NCSA HDF Vset Calls Summary," lists all HDF
Vset routines.
Appendix C, ╥Pre-defined Fieldnames,╙ lists all HDF predefined
fieldnames.
Appendix D, "Source Files," lists the source files needed for HDF
Vsets and describes how to compile and create applications that use
the HDF Vset.
Appendix E, "Compatibility Information for 1.0 Users," offers
important compatibility information for NCSA HDF Vset 1.0
users.
Appendix F, "Obtaining NCSA Software," outlines the procedures
for obtaining NCSA software.
.c2.Form of Presentation
The material in this manual is presented in text, screen displays,
or command line notation.
Text
In explaining various features and commands, this manual often
presents a word within a paragraph in italics to indicate that the
word is defined within the paragraph, or that it is a significant
term that should be noted and/or is being mentioned for the first
time.
So that they are more easily identifiable within this manuscript,
utilities, variables, integer arguments, routine names, etc. have
been presented in 10 point courier style.
Portions of this manual refer to other portions of the manual where
the other portions explain related topics. These cross references
usually mention the title of sections or chapters enclosed in
quotation marks, such as, see Chapter 1, "NCSA HDF Vset
Basics."
Command Line Format Notation
Throughout this manual, many explanations instruct you to make
entries by typing on the keyboard. These entry instructions are
printed in courier bold type and appear within a paragraph or
on a separate line. The command lines in this manual are
normally shown in lowercase, except in rare instances where
uppercase is required.
When it is necessary for you to press a key that is labeled with
more than one character (such as the RETURN key), this manual
identifies the key with all capital (uppercase) letters. Keys to be
entered are printed in bold type. Keys that are pressed
simultaneously or in succession are linked with a hyphen. For
example, press CONTROL-A.
Further Reading
Detailed information about the basic HDF structure and its calling
interface can be found in NCSA HDF Specifications and also
NCSA HDF Calling Interfaces and Utilities which you may
download via FTP, an archive server, or via U. S. mail. Refer to
Appendix F, "Obtaining NCSA Software," for more details.