9 Advanced VICAR Concepts

9.1   Dataset Structure
9.2   VICAR Label Structure
EXPERT This section expands on two basic concepts introduced in Section 4: datasets and labels. More detailed information on dataset and label structure can be found in The VICAR File Format.

9.1 Dataset Structure

EXPERT The standard structure for VICAR datasets is a file of fixed-length records which consists of the parts listed below. Figure 9.1 is a visual representation of the dataset structure.

EXPERT The binary label is an optional area for storing information about a dataset in free-form binary format. The data in the binary label are not defined by the executive, but by the individual applications. There are two parts to the binary label, the binary header and the binary prefix. The binary header is useful for storing information which may pertain to the entire dataset. The binary prefix consists of a fixed number of bytes from each pixel data line and is useful for storing line-dependent information (e.g., marking "bad" data). The binary label is hidden from programs unless they specifically request access to it. If a program does request access, the binary label is then treated as a part of the data. If access is not requested, the binary label will not be present in the output dataset.

EXPERT The pixel data portion of a dataset may contain between 1 and 2.147E9 (2 to the power of 31, minus 1) lines, each of the same length. The maximum length is dependent upon the storage device. Each line is a sequence of pixels whose format is represented by 1, 2, 4 or 8 bytes (Table 4.3.3) and is fixed for a given dataset. In the "picture" interpretation, each line of a dataset represents one raster scan line. The sequence of lines represents the sequence of raster scan lines beginning with line 1 and proceeding down. Multi-dimensional pixel data can be organized in one of three ways: band-sequential (BSQ), band-interleaved by line (BIL) or band-interleaved by pixel (BIP). Additional information on multi-dimensional pixel data organization can be found in the VICAR Run-time Library Reference Manual.

9.2 VICAR Label Structure

EXPERT The VICAR label is an ASCII string containing free-field items of the form keyword=value (Section 4.4.1) separated by spaces.

EXPERT The VICAR label contains three classes of information. Dataset description ("system") items describe the size, organization, data format, and existence of the optional sections of the dataset. "Property" items describe properties of the image in the image domain, such as the map projection, lookup table, and latitude/longitude information. "History" items describe the history of the pixel data in the dataset, the procs that have processed the pixel data, sometimes their parameters, the user identification, and the processing date and time.

EXPERT System items in the VICAR label include, in order:

LBLSIZE		the size of the label in bytes
FORMAT		the data format of the pixels in the image
		(byte, half, full, real, doub, or comp; word
		long, and complex may also be found but are
TYPE		the dataset type (image, param, graph1, graph2
		graph3, tabular)
BUFSIZ		(obsolete, but still required; set it equal to
		RECSIZE in new files) the internal blocksize 
		VICAR will use during I/O
DIM		the number of dimensions in the file (always
		equals 3)
EOL		end-of-dataset label (if there is an EOL, EOL=1)
RECSIZE		the size in bytes of each record in the VICAR
ORG		data organization:
		BSQ	band sequential
		BIL 	band interleaved by line 
		BIP	band interleaved by pixel
NL		number of lines (number of records)
NS		number of samples (record length)
NB		number of image bands (number of data planes)
N1		equal to NS or NB depending on pixel data 
		organization (ORG - Table 9.2) 
N2		equal to NL, NS or NB depending on pixel data 
		organization (ORG - Table 9.2) 
N3		equal to NB or NL depending on pixel data 
		organization (ORG - Table 9.2) 
N4		not yet used; defaults to 0
NBB		number of binary prefix bytes
NLB		number of binary header records
HOST		the type of computer used to generate the
		image (alliant, cray, decstatn, hp-700,
		mac-aux, mac-mpw, sgi, sun-3, sun-4, tek,
INTFMT		format used ot represent integer pixels
		(byte, half, and full) in the file. (low, for 
		vax-vms and decstatn; high for all other
		except cray, which isn't implemented yet)
REALFMT		format used to represent floating-point
		pixels (real, doub, and comp) in the file.
		(rieee for decstatn; vax for vax-vms; ieee
		for all others except cray which isn't
		implemented yet)
BHOST		type of computer used to generate the
		binary label. (same values as HOST)
BINTFMT		format used to represent integers in the
		binary label (same values as INTFMT)
BREALFMT	format used to represent floating-point
		data in the binary label (same values as
BLTYPE		type of binary label



	   Table  9.2  VICAR Data Organization 

EXPERT Property labels are located between the system and the history labels. They begin with the first occurrence of the keyword PROPERTY and end with the first occurrence of the keyword TASK. A dataset may exclude property labels entirely. Each property begins with a PROPERTY keyword, which is the name of the property set. This is followed by the label items that make up the property. The valid property names, and the keywords that make up each property, are defined in a name registry maintained by the VICAR system programmer.

EXPERT History items in the VICAR label include:

TASK		a proc that has processed the dataset
USER		user identification (login id.)
DAT_TIM		processing date and time
optional items	added by the application proc listed under task
Example: History items added by VICAR
	DAT_TIM='Wed Nov 12 19:06:24 1986'
	PARMS='AUTO-STRETCH:    0 to    0 and   138 to   255'
EXPERT The contents of a VICAR label may be listed either as formatted ASCII or as an ASCII dump (Appendix 10.12).

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