IBM Visualization Data Explorer User's Guide

Appendix B. Importing Data: File Formats

Partial Table-of-Contents

Importing your data into Data Explorer will be the first step in creating a visualization of that data. In order to take this step you should have some understanding of the Data Explorer data model and a working knowledge of a Field. An informal description of a Field is provided in Chapter 2. "Introduction to Visualization". A formal description is given in Chapter 3. "Understanding the Data Model".

A number of methods for importing data are available for use with Data Explorer: the General Array Importer, Data Explorer native file format, netCDF, CDF, and HDF.

B.1 General Array Importer: Keyword Information from Data Files

In addition to the syntaxes for the grid, points, and positions keywords described in IBM Visualization Data Explorer QuickStart Guide, it is also possible to derive information for these keywords directly from the data file. This allows you to write "filters" for specific applications that output their data in a set format which includes the grid size within the file.

The syntax for the grid keyword is (in addition to the syntax given in 5.3 , "Header File Syntax: Keyword Statements" in IBM Visualization Data Explorer QuickStart Guide):

                        bytes n                                      bytes n
grid =  [format],[type]{lines n   , [skip, width] [skip, width],..  {lines n, ...
                        marker string                                marker string

where:

format	is the format in which the grid values will be found, and must be one of the following: binary, ieee, text, or ascii. The first two parameters are synonymous, as are the second two.
type	is the type of the values, and should be one of the following: byte int short unsigned byte signed int signed short signed byte unsigned int unsigned short Note that in each of the three groupings shown here, the first and second (reading down) are equivalent to each other.
bytes, lines, and marker	specify where to begin reading the grid values.
skip, and width	are optional and should be used when two pieces of information are on the same line with other information separating them (see Example 2). If necessary, different portions of the grid specification can be read separately by repeating the bytes, lines, or marker specification (see Example 3).

Example 1

   dimensions 100 300

You can specify that this information is to be derived from the data file by the following statement:

   grid = lines 0, 11, 3, 1, 3

You could also have used the statement

   grid = bytes 11

which simply specifies that the grid information will be found after skipping 11 bytes in the file.

Example 2

Suppose the that data file contains the following line (not at the top of the file)

  xdim = 5 ydim = 20

You could use the statement

  grid = marker "xdim =", 0, 2, 8, 2

This specifies that one should start reading after "xdim =," read the first dimension from 2 characters, skip 8 characters, then read the second dimension from 2 characters.

Example 3

suppose that the data file contains the following lines

  xsize = 20
  ysize = 30

You could use the statements

  grid = marker "xsize =" X marker "ysize ="

  grid = marker "xsize =",0,3 X lines 1,8,2

The first specifies that the first dimension should be read following the marker "xsize =," and the second dimension should be read following the marker "ysize =." The second statement specifies that the first dimension should be read from 3 characters, after skipping 0 characters following "xsize =," and that the second dimension should be read from 2 characters after skipping 1 line and 8 characters.

The syntax for the points keyword is (in addition to the syntax given in 5.3 , "Header File Syntax: Keyword Statements" in IBM Visualization Data Explorer QuickStart Guide):

                           bytes n
points =  [format],[type]{ lines n   , [skip, width]
                           marker string

where:

format

is the format in which the grid values will be found, and must be one of the following: binary, ieee, text, or ascii. The first two parameters are synonymous, as are the second two. For type and the other parameters, see the preceding description of grid.

The syntax for the positions keyword is (in addition to the syntax given in 5.3 , "Header File Syntax: Keyword Statements" in IBM Visualization Data Explorer QuickStart Guide):

                            bytes n
positions =[format],[type]{ lines n   , [skip, width]  | ?, ...
                            marker string

(This syntax may be used only if you are specifying regular positions: origin and delta pairs for each dimension. As described in IBM Visualization Data Explorer QuickStart Guide, the origins and deltas are specified as origin1, delta1, origin2, delta2, etc.)

format

is the format in which the grid values will be found, and must be one of the following: binary, ieee, text, or ascii. The first two parameters are synonymous, as are the second two. For type and the other parameters, see the description of grid above. A question mark (?) signifies that the default should be used (origin=0 or delta=1) for a particular origin or delta value. This would be used if only the origins or only the deltas are to be found in the file.

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