A.1NCSA HDF Calling Interfaces and Utilities NCSA HDF TagsA.1 National Center for Supercomputing Applications November 1989 November 1989 Appendix ANCSA HDF Tags Overview This appendix includes a table containing brief descriptions of most of the tags that have been assigned at NCSA for general use. The list is growing and will be expanded in future editions of the documentation. More detailed descriptions of the tags can be found in an appendix of the NCSA HDF Specifications. To obtain a draft of this document, contact the NCSA Software Development Group at the address listed on the README page at the beginning of this manual. Tag Types and Descriptions The following table has five columns. The Tag column gives the abbreviated symbolic name of the tag that is often used in an augmented form in HDF programs. The Name column gives a name commonly used in human-readable media. The Data Type column describes the type of data that is associated with the tag, and where possible, gives the amount of data. The Number column gives the actual numeric value that is stored in the file to represent the tag. The Use column describes the tag in brief and general terms. In the table, the term string refers to a sequence of ASCII characters, with a zero byte possibly occurring at the end, but nowhere else. The term text likewise refers to a sequence of ASCII characters, but it may contain zero bytes elsewhere than at the end. Table A.1 HDF Tags TagNameDatatypeNumberUse Utility Tags DFTAG_NULLNo Datanone001used for place holding and filling up empty portions of the Data Descriptor Block. DFTAG_RLERun length encoding0 bytes011specifies that run length encoding is used to compress an image. DFTAG_IMCIMCOMP0 bytes012specifies that IMCOMP compression is used to Compressioncompress an image. DFTAG_FIDFile Identifierstring100points to a string that the user wants to associate with this file. It is intended to be a user-supplied title for the file. DFTAG_FDFile Descriptortext101points to a block of text describing the overall file contents. It is intended to be user-supplied comments about the file. DFTAG_TIDTag Identifierstring102provides a way for a human reader to tell the meaning of a tag stored in a file. DFTAG_TDTag Descriptortext103similar to TID, but allows more extensive text to be included. DFTAG_DILData Identifier Labelstring104 associates the string with the Data Identifier as a label for whatever that Data Identifier points to in turn. By including DILs, any piece of data can be given a label for future reference. For example, this is often used to give titles to images. DFTAG_DIAData Identifier text105associates the text block with the Data AnnotationIdentifier as annotation for whatever that Data Identifier points to in turn. With DIA, any Data Identifier can have a lengthy, user-written description of why that data is in the file. DFTAG_NTNumber Type4 bytes106used by any other element in the file to indicate specifically what a numeric value looks like. DFTAG_MTMachine Type0 bytes107specifies that all unconstrained or partially constrained values in this HDF file are of the default type for that hardware. Table A.1 HDF Tags (Continued) TagNameData TypeNumberUse Raster-8 (8-Bit Only) Tags DFTAG_ID8Image Dimension-84 bytes200two 16-bit integers representing the width and height of an 8-bit raster image in bytes. DFTAG_IP8Image Palette-8768 bytes201a 256 x 3 byte array representing the red, green and blue elements of the 256-color palette respectively. DFTAG_RI8Raster Image-8x*y bytes202a row-wise representation of the elementary 8-bit image data. DFTAG_CI8Compressed Image-8n bytes203a row-wise representation of the elementary 8-bit image data. Each row is compressed using a form of run-length encoding. DFTAG_II8IMCOMP Image-8n bytes204a 4:1 compressed 8-bit image, using the IMCOMP compression scheme. General Raster Image Tags DFTAG_IDImage Dimension20 bytes300defines the dimensions of the 2D array that its corresponding RI tag refers to. DFTAG_LUTLook Up Tablen bytes301table to be used by hardware to assign RGB colors or HSV colors to data values. DFTAG_RIRaster Imagex*y bytes302points to raster image data. DFTAG_CICompressed Imagen bytes303points to a compressed raster image. DFTAG_RIGRaster Image Groupn*4 bytes306lists the Data Identifiers (tag/ref) that describe a raster image set. DFTAG_LDLUT Dimension20 bytes307defines the dimensions of the 2D array that its corresponding LUT tag refers to. DFTAG_MDMatte Dimension20 bytes308defines the dimensions of the 2D array that its corresponding MA tag refers to. DFTAG_MAMatte Datan bytes309points to matte data. DFTAG_CCNColor Correctionn bytes 310specifies the Gamma correction for the image and color primaries for the generation of the image. DFTAG_CFMColor Formatstring311indicates what interpretation should be given to each element of each pixel in a raster image. DFTAG_ARAspect Ratio4 bytes312indicates the visual aspect ratio for this image. Table A.1 HDF Tags (Continued) TagNameData TypeNumberUse Composite Image Tag DFTAG_DRAWDrawn*4 bytes400identifies a list of Data Identifiers (tag/ref) which define a composite image. DFTAG_RUNRunn bytes401identifies code that is to be executed as a program or script. Tag for Composite or Raster Images DFTAG_XYPXY Position8 bytes500indicates an XY position on the screen for composites and other groups. Vector Image Tags DFTAG_T14Tektronix 4014n bytes602points to a Tek 4014 data stream. The bytes in the data field, when read and sent to a Tektronix 4014 terminal, will be displayed as a vector image. DFTAG_T105Tektronix 4105n bytes603points to a Tek 4105 data stream. The bytes in the data field, when read and sent to a Tektronix 4105 terminal, will be displayed as a vector image. Scientific Data Set Tags DFTAG_SDGScientific Data Groupn*4 bytes700lists the Data Identifiers (tag/ref) that describe a scientific dataset. DFTAG_SDDScientific Datan bytes701defines the rank and dimensions of the Dimension Recordarray that the corresponding SD refers to. DFTAG_SDScientific Datareals702points to scientific data. DFTAG_SDSScalesreals703shows scales to be used when interpreting and displaying data. DFTAG_SDLLabelsstrings704labels for all dimensions and for the data. DFTAG_SDUUnitsstrings705displays units for all dimensions and for the data. DFTAG_SDFFormatsstrings706formats for displaying axes and data. DFTAG_SDMMax/min2 reals707shows maximum and minimum values for the data. DFTAG_SDCCoordinate systemstring708shows coordinate system to be used to interpret data. DFTAG_SDTTranspose0 bytes709indicates that data is transposed in the file.