# HDF User’s Guide

Version 4.2r4

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> 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:

> - Table A: The HDF Utility Tags. Used by the HDF utilties.
> - Table B: The HDF General Raster Image Tags. Used to describe aspects of raster image data.
> - Table C: The HDF Composite Image Tags. Used to describe aspects of composite image data.
> - Table D: The HDF Scientific Data Set Tags: Used to describe aspects of scientific data set (SDS) data.
> - Table E: The HDF Vset Tags. Used to describe aspects of HDF Vset data.
> - Table F: The Obsolete HDF Tags: Used to describe aspects of HDF data elements that have been replaced by newer tags or discontinued.
> 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