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Chapter 9: Spreadsheets and Plots

A JHV spreadsheet is designed to display the raw data of an image or a Vdata table. The spreadsheet displays data that can be defined in terms of three variables: two independent variables which correspond to the row and column labels, and a dependent variable, which has a value at every point. JHV supports two types of spreadsheet: image spreadsheets and Vdata spreadsheets. An image spreadsheet is created from an image which represents an HDF raster image or an SDS data array. A Vdata spreadsheet is a table which displays a Vdata.
9.1 Image Spreadsheets
9.2 Vdata Spreadsheets
9.3 Vdata X-Y Plots


9.1 Image Spreadsheets

JHV has the ability to generate a spreadsheet from an image. Select a subset area from the image in the image window and click the spreadsheet button to create a spreadsheet containing the data of the selected image area.


Figure 9.1 An image spreadsheet

The current image spreadsheet supports a Make Image action. Make Image creates an image from the spreadsheet. There are two parameters associated with creating an image from a spreadsheet: an expansion factor and interpolation.

Expansion factor
The expansion factor determines the magnification of the image created from the spreadsheet. The factor values are integers such as 1, 2, 3, and so on. An image with expansion factor 1 is the same size as the original selected image area. An image with expansion factor 2 will be double the original image size, and so forth. Larger expansion factors will produce lower resolution images with a jagged appearance.

Interpolation
The interpolation option attempts to choose color values that better preserve the quality and detail in the original image. Interpolation is very useful when you create an image with a larger expansion factor. A large expansion factor with no imterpolation will yield a jagged appearance because the resolution does not increase with the magnification of the image. Interpolation produces an image with the resolution of the original image even for larger expansion factors. In the following figure, two images have been created from the same spreadsheet with expansion factor 10. The left image, with a jagged appearance, was created without interpolation. The image on the right, with a smoother appearance, was created with interpolation.


Figure 9.2 Image interpolation

9.2 Vdata Spreadsheets

A Vdata object is a table in which each row has the same structure and each column contains data of the same data type. A column can be any of data type, such as character, integer, floating point, or an array of these types. Therefore, a cell in a Vdata table can be an array. Elements may be cut off in display if a cell is an array.

To open a Vdata spreadsheet, click on a Vdata object icon in the HDF hierarchical tree in the main window. The spreadsheet will appear in a spreadsheet window.

The spreadsheet window File menu offers three commands:

Save AS HDF
Saves the current Vdata into a new HDF file.
Save AS Text
Saves the Vdata into a new ASCII file.
Close
Closes the spreadsheet window.


Figure 9.3 A Vdata spreadsheet

9.3 Vdata X-Y Plots

Clicking on a column with numeric data in a Vdata spreadsheet opens a plot window with the column values plotted against the row index numbers. Clicking on another column adds that column to the plot. The Vdata spreadsheet cannot create plots for columns containing arrays or character data.

The following is an example of Vdata plot with two columns (Integer and Float) plotted against the row index.


Figure 9.4 A Vdata X-Y plot

The Vdata plot window offers three menus:

Option menu
Line-Plot
XY-Plot

The Option menu contains two commands: Line-Plot and XY-Plot. A line-plot is a 2D plot in which columns (vertical axis) are plotted against the row index (horizontal axis). An X-Y plot is a plot in which columns are plotted against the first selected column.

View menu
Zoom In
Zoom Out

The View menu provides zooming in and zooming out functions. Zoom In decreases the range of visible rows in the plot; Zoom Out increases the visible range.

Style menu
Line
Scatter

The Line style provides a line plot. With the Scatter style, column values are scattered on the plot.


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