The HDF Group

HDF User’s Guide

Version 4.2r4


[Top]


Appendices
Appendix A Reserved HDF Tags
A.1 Overview

This appendix includes tables containing brief descriptions of most of the tags that have been reserved for general use. This list will be expanded in future editions to include new tags as they are assigned. A more detailed description of the tags can be found in the HDF Specification and Developer's Guide. Also see the HDF Specification and Developer's Guide for a description of extended tags, which are not discussed in this appendix.

Each table contains a list of tags within one category. The titles of the tables, with a functional description of each table, are:

A.2 Tag Types and Descriptions

The following tables have five columns:

Tag Name contains the abbreviated symbolic names of tags that are often used in an augmented form in HDF programs.
Short Description contains a brief (four word maximum) description of the tag that is commonly used to describe to the tag in HDF manuals and in-line code documentation.
Data Size describes the type of data that is associated with the tag and, where possible, lists the data size.
Tag Value lists the numeric value of the tag symbol in the hdf.h header file.
Long Description contains a general description of the tag.

In the tables, the term String refers to a sequence of ASCII characters with the null byte possibly occurring at the end, but nowhere else. The term Text also refers to a sequence of ASCII characters, but it may contain null characters anywhere in the sequence. An n in the Data Size column describes a data unit of variable-length. For more detailed descriptions of these units of data, refer to the appropriate tag entry in the HDF Specification and Developer's Guide.

TABLE A The HDF Utility Tags
Tag Name
Short Description
Data Size
Tag Value
Long Description
DFTAG_NULL
No Data
None
001
Used for place holding and filling up empty portions of the Data Descriptor Block.
DFTAG_VERSION
Library Version Number
4 bytes + string
030
Specifies the latest version of the HDF library used to write to the file.
DFTAG_NT
Number Type
4 bytes
106
Used by any other element in the file to specifically indicate what a numeric value looks like.
DFTAG_MT
Machine Type
0 bytes
107
Specifies that all unconstrained or partially constrained values in this HDF file are of the default type for that hardware.
DFTAG_FID
File Identifier
String
100
Points to a string that the user wants to associate with this file. This supports the inclusion of a user-supplied title for the file.
DFTAG_FD
File Descriptor
Text
101
Points to a block of text describing the overall file contents. It is intended to be user-supplied comments about the file.
DFTAG_TID
Tag Identifier
String
102
Provides a way to determine the meaning of a tag stored in the file.
DFTAG_TD
Tag Descriptor
Text
103
Similar to DFTAG_TD, but allows more text to be included.
DFTAG_DIL
Data Identifier Label
String
104
Associates the string with the Data Identifier as a label for whatever the identifier points to. By including DILs, any data element can be given a label for future reference. For example, this tag is often used to give titles to raster image data sets.
DFTAG_DIA
Data Identifier Annotation
Text
105
Associates the text block with the Data Identifier as an annotation for whatever that Data Identifier points to. With DIAs, and Data Identifier can have a lengthy, user-provided description of why that particular data element is in the file.
DFTAG_RLE
Run-length Encoding
0 bytes
011
Specifies that run-length encoding (RLE) is used to compress a raster image.
DFTAG_IMC
IMCOMP
Compression
0 bytes
012
Specifies that IMCOMP compression is used to compress a raster image.
DFTAG_JPEG
24-bit JPEG
Compression
n bytes
013
Provides header information for 24-bit JPEG-compressed raster images.
DFTAG_GREYPEG
8-bit JPEG
Compression
n bytes
014
Provides header information for 8-bit JPEG-compressed raster images.
TABLE B The HDF General Raster Image Tags
Tag Name
Short Description
Data Size
Tag Value
Long Description
DFTAG_RIG
Raster Image Group
n*4 bytes
306
Lists the Data Identifiers (tag/reference number pairs) that uniquely describe a raster image set.
DFTAG_ID
Image Dimension
20 bytes
300
Defines the dimensions of the two-dimensional array the corresponding RI tag refers to.
DFTAG_LD
LUT Dimension
20 bytes
307
Defines the dimensions of the two-dimensional array the corresponding LUT tag refers to.
DFTAG_MD
Matte Dimension
20 bytes
308
Defines the dimensions of the two-dimensional array the corresponding MA tag refers to.
DFTAG_RI
Raster Image
x*y bytes
302
Points to a raster image data set.
DFTAG_CI
Compressed Image
n bytes
303
Points to a compressed raster image data set.
DFTAG_LUT
Lookup Table
n bytes
301
Table to be used by the hardware for the purpose of assigning RGB or HSV colors to data values.
DFTAG_MA
Matte Data
n bytes
309
Points to matte data.
DFTAG_CCN
Color Correction
n bytes
310
Specifies the gamma correction for the raster image and color primaries used in the generation of the image.
DFTAG_CFM
Color Format
String
311
Indicates the interpretation to be given to each element of each pixel in a raster image.
DFTAG_AR
Aspect Ratio
4 bytes
312
Indicates the aspect ratio of the image.
DFTAG_XYP
XY Position
8 bytes
500
Specifies the screen X-Y coordinate for raster image sets. (Also used for composite image sets - See the entry for DFTAG_XYP in Table 12.6)
TABLE C The HDF Composite Image Tags
Tag Name
Short Description
Data Size
Tag Value
Long Description
DFTAG_DRAW
Draw
n*4 bytes
400
Specifies a list of Data Identifiers (tag/reference number pairs) which define a composite image.
DFTAG_XYP
XY Position
8 bytes
500
Specifies the screen X-Y coordinate for composite image sets. (Also used for raster image sets - See the entry for DFTAG_XYP in Table 12.5)
DFTAG_RUN
Run
n bytes
401
Identifies code that is to be executes as a program or script.
DFTAG_T14
Tektronix 4014
n bytes
602
Used as a vector image tag. Points to a Tektronix 4014 data. The bytes in the data field, when read and sent to a Tektronix 4014 terminal, will be displayed as a vector image.
DFTAG_T10S
Tektronix 4015
n bytes
603
Used as a vector image tag. Points to a Tektronix 4015 data. The bytes in the data field, when read and sent to a Tektronix 4015 terminal, will be displayed as a vector image.
TABLE D The HDF Scientific Data Set Tags
Tag Name
Short Description
Data Size
Tag Value
Long Description
DFTAG_NDG
Numeric Data Group
n*4 bytes
720
Lists the Data Identifiers (tag/reference number pairs) that describe a scientific data set. Supersedes DFTAG_SDG.
DFTAG_SDD
SDS Dimension Record
n bytes
701
Defines the rank and dimensions of the array the corresponding SD refers to.
DFTAG_SD
Scientific Data
Real Number
702
Points to scientific data.
DFTAG_SDS
SCales
Real Number
703
Identifies the scales to be used when interpreting and displaying data.
DFTAG_SDL
Labels
String
704
Labels all dimensions and data.
DFTAG_SDU
Units
String
705
Displays units for all dimensions and data.
DFTAG_SDF
Formats
String
706
Displays formats for axes and data.
DFTAG_SDM
Maximum/minimum
2 Real Numbers
707
Displays the maximum and minimum values for the data.
DFTAG_SDC
Coordinate system
String
708
Displays the coordinate system to be used in interpreting data.
DFTAG_SDLNK
SDS Link
8 bytes
710
Links and old-style DFTAG_SDG and a DFTAG_NDG in cases where the DFTAG_NDG meets all criteria for a DFTAG_SDG.
DFTAG_CAL
Calibration Information
36 bytes
731
The calibration record for the corresponding DFTAG.SD.
DFTAG_FV
Fill Value
n bytes
732
The value which has been used to indicate unset values in the corresponding DFTAG_SD.
TABLE E The HDF Vset Tags
Tag Name
Short Description
Data Size
Tag Value
Long Description
DFTAG_VG
Vgroup
14+n bytes
1965
Provides a general-purpose grouping structure.
DFTAG_VH
Vdata Description
22+n bytes
1962
Provides information necessary to process a DFTAG_VS.
DFTAG_VS
Vdata
n bytes
1963
Contains a block of data that is to be interpreted according to the information in the corresponding DFTAG_VH.
TABLE F The Obsolete HDF Tags
Tag Name
Short Description
Data Size
Tag Value
Long Description
DFTAG_IDS
Image Dimension-8
4 bytes
200
Two 16-bit integers that represent the width and height of an 8-bit raster image in bytes.
DFTAG_IP8
Image Palette-8
768 bytes
201
A 256 x 3 byte array representing the red, green and blue elements of the 256-color palette respectively.
DFTAG_RI8
Raster Image-8
x*y bytes
202
A row-oriented representation of the elementary 8-bit image data.
DFTAG_CI8
Compressed Image-8
n bytes
203
A row-oriented representation of the elementary 8-bit raster image data, with each row compressed using a form of run-length encoding.
DFTAG_II8
IMCOMP Image-8
n bytes
204
A 4:1 8-bit raster image, compressed using the IMCOMP algorithm.
DFTAG_SDG
Scientific Data Group
n*4 bytes
700
List the Data Identifiers (tag/reference number pairs) that uniquely describe a scientific data set.
DFTAG_SDT
Transpose
0 bytes
709
Indicates that data is transposed in the file.
Appendix B HDF Installation Overview
B.1 General HDF Installation Overview
B.1.1 Acquiring the HDF Library Source

You may obtain the HDF source code and/or selected binaries at no charge from The HDF Group's server:

http://www.hdfgroup.org/products/hdf4

http://www.hdfgroup.org/release4/obtain.html

For reference, the unpacked HDF source code can be found at

ftp://ftp.hdfgroup.org/HDF/HDF_Current/src/unpacked/.

B.1.2 Building the HDF Library Source

For instructions on building HDF from the source code, please refer to the INSTALL file in the top directory of the unpacked HDF source tree.


HDF4.2r4 - February 2009
Copyright
The HDF Group
www.hdfgroup.org
The HDF Group