#!F-adobe-helvetica-medium-r-normal--18* #!N #!CSeaGreen #!N #!Rall110 Describing the Data #!N #!EC #!N #!N To import data through the General Array Importer, you must be able to answer the following questions. #!N #!N #!I0 #!N #!F-adobe-times-medium-r-normal--18* #!N #!N #!I30 #!N 1. What are the independent and dependent variables? For example, if temperature and wind velocity are measured on a latitude-longitude grid, then latitude and longitude are the independent variables, temperature and wind velocity the dependent variables. In the case of resistance measurements versus the voltage applied to a semiconductor, voltage is the independent variable and resistance the dependent variable. #!CIndianRed #!N #!N #!N #!F-adobe-times-bold-r-normal--18* Components and Variables #!N #!N In Data Explorer terminology, the values of the independent variable constitute the "positions" component of a data field. In the examples above, the first independent variable consists of locations in space and the second does not, but both would be represented as "positions" in a data field. The independent variable is #!F-adobe-times-medium-i-normal--18* always #!EF represented by the "positions" component. #!N #!N The values of the dependent variable constitute the "data" component. #!N #!N #!EC #!N #!I30 #!N 2. What is the dimensionality of the positions and data components? In the first example above, latitude and longitude are represented by 2-dimensional positions, the temperature by scalar data, and the wind velocity by 2- or 3-dimensional vectors. In the second example, voltage is represented by 1-dimensional positions and the resistance by scalar data. #!N #!I30 #!N 3. How is the independent variable (the set of positions) to be described? By a regular grid (which can be completely described by an origin and a set of deltas) or by an explicit list (which may or may not be part of the data file)? For example, data measurements might be on a grid of 1-degree increments in latitude and 5-degree increments in longitude; voltage levels might be a set of unrelated values stored with the resistances in the data file. #!N #!I30 #!N 4. How are the positions connected to one another, if they are connected? For example, a regular grid of positions might be connected by a regular grid of connections (lines, quads, or cubes). The connections specify how data values should be interpolated between positions. Positions that are explicitly specified (i.e., not regular) can also be connected by a regular grid of connections (e.g., if the grid is deformed, or warped). See #!Lgrdtyps11,dxall111 f Figure 11 #!EL . #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rgrdtyps11 #!N Graphics omitted from Online Documentation. Please see the manual. #!N #!N Figure 11. Examples of Grid Types. The three grids in the top row represent surfaces; those in the bottom row, volumes. Reading from left to right, the three types of grid are: irregular (irregular positions, irregular connections), deformed regular (irregular positions, regular connections), and regular (regular positions, regular connections), #!EF #!N #!EC #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rcoldpnd12 #!N Graphics omitted from Online Documentation. Please see the manual. #!N #!N Figure 12. Examples of Data Dependency. In the visualization on the left, data correspond one-to-one with positions. Other data values (and colors) are interpolated linearly between positions. In the visualization on the right, the elements connecting positions are quads. Data (and colors) correspond one-to-one with, and are constant within, each quad. #!EF #!N #!EC Note: The General Array Importer supports only regular connections (lines, quads, and cubes) or scattered data. For irregular connections such as triangles or tetrahedra, you can use the Data Explorer native format to import your data. (See IBM Visualization Data Explorer User's Guide.) #!N #!I30 #!N 5. What is the format of the stored data values, ASCII or binary? Are they floating point, integer, signed or unsigned byte, etc.? #!N #!I30 #!N 6. Are the data dependent on "positions" or on "connections"? That is, are the data values associated one-to-one with positions or with the connections between positions? See #!Lcoldpnd12,dxall111 f Figure 12 #!EL . (Data associated with connections are often referred to as "cell-centered.") With position-dependent data, values between positions are interpolated within the connection element. With connection-dependent data, values are assumed to be constant within the connection element. #!N #!I30 #!N 7. Do these data values represent "series data" or do they constitute only a single frame of data? In the example of resistance levels versus voltage, data may exist for each of a number of different doping levels. Each doping level could be considered a single data field and the collection treated as a series. #!N #!I30 #!N 8. Is the data in "record" or "spreadsheet" style? (See #!Lboxes114,dxall113 f Figure 14 #!EL .) #!N #!I30 #!N 9. If the data are on a grid, what is the order of the data items with respect to the grid? Is it column majority (first index varies fastest) or row majority (last index varies fastest)? (See #!Lrowcol13,dxall111 f Figure 13 #!EL .) #!N #!I30 #!N 10. What kind of embedded text (comments, etc.) in the data file must be "skipped" when the data values are read? #!N #!I0 #!N #!EF #!N #!N #!N With the answers to these questions, you can now use the General Array Importer to describe your data. #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rrowcol13 #!N Graphics omitted from Online Documentation. Please see the manual. #!N #!N Figure 13. Row- versus Column-Majority Grids. The two grids shown here are generated from the same data file, consisting simply of the numbers 1, 2, 3, ..., 20. The associated header files differ only in the specification of the grids' majority. #!EF #!N #!EC #!N #!N #!N #!F-adobe-times-medium-i-normal--18* Next Topic #!EF #!N #!N #!Lall111,dxall112 h Creating a Header File #!EL #!N #!F-adobe-times-medium-i-normal--18* #!N
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