2.5 Controlling the Appearance of an Object: The Image Window

Controlling the appearance of an object means being able to control various aspects of its visual image on the screen as well as the data used in generating that image. This section deals briefly with control of the following aspects:

• the object's appearance (size and the "view" displayed in the Image window)
• the sequence in which object images are presented
• the input from which an object's image is generated
• the color(s) of an object
• the placement of axes around an object.

Note: Throughout this document, the term "Image window" refers to the window generated by Image (not by Display). Both of these modules are described in IBM Visualization Data Explorer User's Reference. Also see IBM Visualization Data Explorer User's Guide for a comprehensive treatment of the user interface.

Size, View, and AutoAxes

In Data Explorer the most easily controlled feature of an object in the Image window is its size, which can be changed by direct manipulation of the window. Other important features of its appearance are controlled through two options in the Options pull-down menu in the Image window menu bar: View Control and AutoAxes.

Size Control

To change the size of an image, simply change the size of the Image window. Holding down the left mouse button:

• Drag a horizontal border to shrink or expand the window vertically.
• Drag a vertical border to shrink or expand the window horizontally.
• Drag a corner to shrink or expand a window vertically and horizontally.

Notes:

1. Reset in the Options pull-down menu restores the original view of the object but not the original size of the window.
2. If your visual program uses the Display rather than the Image tool, the image size can be changed only by changing the resolution parameter of Camera or AutoCamera (see Camera and AutoCamera in IBM Visualization Data Explorer User's Reference for descriptions of these tools.)

View Control

• Viewing direction
• Rotation
• Field of view (zooming and panning).

To open this dialog box, select View Control... in the Options pull-down menu in the Image window.

Controlling the Viewing Direction

To change the viewing direction, select Set View in the dialog box (see Figure 6). The list of choices that appears includes 7 directional views of the object (Top, Bottom, etc.). Because these "head on" views show only "one side" of an object (tending to flatten its appearance), the list also offers 7 corresponding "off" views (Off Top, Off Bottom, etc.).

Figure 6. View Control Dialog Box. This dialog box is activated from the Options pull-down menu of the Image window (see Figure 5).

When you select a view of an object, the image is automatically altered (note the highlighted Execute in the menu bar).

Controlling Rotation

To rotate an object in the Image window, first click on the Mode option box (initially displaying None) and then select Rotate from the displayed list. Rotate becomes the current mode and a set of axes appears in the lower right-hand corner of the window. You can rotate the object in two dimensions (clockwise and counterclockwise) or in three by rotating the axes. You can also cause the object to rotate "continuously" (i.e., in coordination with the axes).

2-D Rotation	Position the mouse cursor in the Image window and hold down the right mouse button: clockwise movement of the mouse produces clockwise rotation of the axes; counterclockwise movement produces counterclockwise rotation. When the mouse button is released, the object rotates by the same amount as the axes have, assuming the same relative position in the window.
3-D Rotation	Position the mouse cursor in the Image window and hold down the left mouse button: the mouse now behaves like a track ball and the axes move accordingly. When the mouse button is released, the object rotates by the same amount as the axes have, assuming the same relative position in the window.
Continuous Rotation	Once you have selected Rotate mode, you can make the object rotate along with the axes: select Execute in the menu bar and then Execute on Change in the pull-down menu (Execute is highlighted). The image is now replaced by a dot representation of the object (see rendering options in IBM Visualization Data Explorer User's Guide). The movement of the mouse (and the axes) is reflected directly and continuously in the movement of this dot version. Note: Movement of the axes is essentially synchronous with movement of the mouse, but the "response time" of the dot version may vary, depending on the machine and configuration.

Notes:

1. Turn off Execute on Change by selecting End Execution in the Execute pull-down menu.
2. To restore the original view of the object, select Reset in the View Control dialog box.

Controlling the Field of View

Zoom mode allows you to enlarge an object, making it appear closer (zooming in) or to reduce it, making it appear more distant (zooming out).

Pan/Zoom mode allows you to change the center of focus while zooming in or out.

Zooming in:

1. Select Zoom in the Mode option list of the dialog box.
2. To zoom in, position the mouse cursor in the Image window and hold down the left mouse button. An overlay rectangle appears.
3. You can enlarge or shrink this rectangle by moving the mouse cursor away from or toward the center of the window.
4. When you release the mouse button, the area of the rectangle expands to fill the Image window, making the object appear nearer.

   Note: If you simply click the mouse button instead of holding it down, the overlay rectangle will disappear before you can change its dimensions. The modified image of the object will be based on that rectangle. (The size of the rectangle and thus the degree of "zoom" depends on the distance of the cursor from the center of the window when you first press the mouse button.)

5. To cancel the effect of the most recent command, select Undo in the dialog box or in the Options pull-down menu. You can also repeat a command that has been "undone," by selecting Redo.

   Note: Since executed commands are maintained in a stack, you can undo those commands one by one and redo them, too.

6. Reset in the dialog box (or in the Options pull-down) menu restores the original view: (e.g., front) of the object.

1. Follow the procedure described for zooming in, but use the right mouse button.
2. When you release the mouse button, the area of the Image window is reduced to the area of the rectangle, making the object appear more "distant".

1. Select Pan/Zoom in the Mode option list of the dialog box.

2. Position the mouse cursor at the point in the Image window that you want as the center of the new "picture," and press the appropriate mouse button (left to zoom in or right to zoom out).

3. Move the mouse in any direction to display the overlay rectangle. The "zooming" behavior of the object with respect to the rectangle will be the same as that just described.

4. To restore the original view of the object, select Reset in the dialog box.

5. Leave the View Control dialog box open for the next exercise.

AutoAxes Configuration

The AutoAxes Configuration dialog box allows you to generate a set of axes for an object in the Image window and to specify some of its characteristics.

1. Click on Options in the menu bar of the Image window and then select AutoAxes in the pull-down menu. The AutoAxes Configuration dialog box appears.

   Note: To display additional options, click on the Expand button at the bottom of the dialog box. For purposes of this tutorial, you will not be changing any AutoAxes options. For more information, see AutoAxes in IBM Visualization Data Explorer User's Reference.

2. Click on the Enabled toggle button (at the top of the dialog box) to select the AutoAxes option. The button is now activated.

3. Click on OK or Apply at the bottom of the dialog box to confirm the selection.

   Notes:

   1. OK closes the dialog box; Apply does not.
   2. Selection of Enabled and OK or Apply is necessary but not sufficient to activate the AutoAxes option (see next step).

4. Select Execute in the menu bar and then Execute Once in the pull-down menu.

   The object now appears in an axes box. Because the view is "head on," the box appears to be 2-dimensional. For Diagonal or any of the "Off" views, however, it appears fully 3-dimensional (see next step).

5. To change the view of the object, select another (e.g., Diagonal) from the Set View pull-down list in the View Control... dialog box. The view changes to Diagonal (note that the axes box changes as well).

6. To remove the axes box from the window:

   1. Deactivate the Enabled toggle button in the AutoAxes Configuration dialog box by clicking on it.

   2. Click on OK or Apply.

   3. Again, execute the program (unless it is already in Execute on Change mode). The axes box disappears.

   4. To restore the original view of the object, click on Reset in the View Control dialog box

7. Close the View Control dialog box (by clicking on Close) and the AutoAxes Configuration dialog box (by clicking on Cancel).

Figure 7. Sequence Control Panel. The first two buttons at top left are Loop and Palindrome. The others are: Step (<||>), Counter (...), Back (<), Forward (>), Stop (&sqbul;), and Pause (||).

Using the Sequencer

The Sequencer allows you to "animate" a visual image and is very easy to use. The process is rather like running a video cassette tape: You can play it forward or backward, stop it, pause, and so on. (If you look at the canvas of the VPE window, you will see that the Sequencer is one of the components of the example1.net network.)

1. Click on Execute in the menu bar of the Image window and then on Sequencer in the pull-down menu to display the Sequence Control panel (Figure 7).

2. Click on the Forward button (>) to start the animation sequence.

   Note: A Sequencer button appears recessed when it is activated.

   As the sequence proceeds, the Counter button (...) displays the corresponding "frame" number. At the end of the execution cycle, the window displays the final image in the sequence, the Counter displays the final frame number, and the Forward button is deactivated (not recessed).

3. Click on the Back button (<) to run the same sequence in reverse. At the end of the execution cycle, the window displays the original image, the Counter displays "0", and the Back button is deactivated.

4. Click on the Step button (<||>) to activate it. You can now proceed through a sequence frame by frame in either direction, using Back and Forward.

   Note: In Step mode, the Back and Forward buttons appear as <|| and ||> respectively.

5. Click on Step again (to deactivate it) and then on the Loop button at the top left (marked by a single "looped" arrow). Now, if you click on Back or Forward, the sequence will repeat itself until you interrupt it (see the next four steps).

6. Click on the Pause button (||) to suspend the sequence.

7. Continue the sequence from this point or reverse it, using Back or Forward.

8. Click on the Stop button (&sqbul;). The sequence halts (the Loop button remains activated).

   Note: The Stop button does not affect the status of the Loop, Palindrome, or Step button.

9. Click on Back or Forward. A new sequence starts again from the beginning (i.e., a "stopped" sequence cannot be continued or reversed from the point at which you interrupted it).

10. Click on Loop. The sequence continues to its end before stopping and the Loop button is deactivated (compare with the Stop button).

11. Click on the Palindrome button (between Loop and Step). With this option activated, you can use the Back (or Forward) button to run a sequence through one back-and-forth cycle (from first frame to last and back to first, or vice versa). Note that if you activate this function at some intermediate frame in the sequence, only the remainder of the cycle is executed.

12. To restore the original view of the object, click on Reset in the View Control dialog box.

13. Close the Sequence Control panel (double click on the window menu button in top left corner of the frame).

Using Control Panels

Control panels give you direct control of inputs to a visual program. The control panel included with example1.net, for example, allows you to incorporate a colored plane in the image of an object and to decide the number of contour lines to be displayed in that plane. To open the control panel:

1. Select Windows in the menu bar of the Image window.

2. Select Open All Control Panels in the pull-down menu. The control panel appears (see Figure 8).

Figure 8. Control Panel with two Interactors..  

To display a colored plane:

1. Click on off in the Show MapToPlane interactor.

2. Select on when it appears in the selection list.

3. Select Execute in the menu bar of either the control panel or the Image window.

4. Select Execute on Change in the pull-down menu. The visual program reexecutes and the colored plane is incorporated as part of the current image.

5. To specify the number of contour lines, click on one of the two stepper arrowheads in the number of contour lines interactor (right to increase the number, left to decrease it). Since Data Explorer is in Execute on Change mode, the number of contours changes when the number in the interactor changes.

   Notes:

   1. The second interactor has no effect if the first interactor is off.

   2. Depending on opacity and other factors, some of the contour lines "inside" the object may not be visible.

6. Click on on in the Show MapToPlane interactor and then select off when it appears. The plane disappears and the original image is restored.

Using the Colormap Editor

The example1.net visual program includes a Colormap Editor for controlling the color characteristics of data values represented in the visual image. The editor also controls the opacity of those values (see Table 1).

Opening the Colormap Editor:

1. Select Open All Colormap Editors in the Windows pull-down menu of the Image window. Now changes made in the Colormap Editor (Figure 9) will be reflected both in the editor and in the image. (Data Explorer should still be in Execute on Change mode from the preceding exercise. If not, select that mode in any Execute pull-down menu.) For example:

2. Move the mouse cursor into the large rectangle under the Hue label button (the cursor changes from an arrow to a circle with sight marks).

3. Use the left mouse button to drag the control point (the small box in the upper left-hand corner of the rectangle) horizontally to a position under Hue. The color column to the left changes as the point moves.

   Note: The Hue button is automatically activated when the mouse button is pressed with the cursor positioned in the Hue rectangle.

4. Release the mouse button. Color changes appear in the object.

5. Drag the control point back to its original position and release the mouse button. The color column and the object return to their original states.

Table 1. Image Characteristics Controlled by the Colormap Editor

Characteristic	Description	Numerical Range/ Image Values
Hue	A particular color	0.000 = Red 0.333 = Green 0.666 = Blue 1.000 = Red
Saturation	Purity of color	0.0 = White (all colors) 0.5 = "Pastel" (50% of one color) 1.0 = Pure (100% of one color)
Value	Degree of brightness	0.0 = Black (0% brightness) 0.5 = Dark (50% brightness) 1.0 = Maximum (100% brightness)
Opacity	Degree of transparency	0.0 = 0% Opaque (100% transparent) 0.5 = Semi-opaque (50% transparent) 1.0 = 100% Opaque (0% transparent)
The numerical range used in specifying discrete values of a characteristic is 0.0-1.0. Corresponding Colormap values at the limits and middle of a range are also listed.

Before going any further, you should familiarize yourself briefly with the Colormap Editor (Figure 9). Note that the four labeled rectangles to the right correspond to the characteristics listed in Table 1. In each rectangle, at least two control points (very small "boxes") and a line connecting them determine how the image characteristics associated with a particular data value are represented in the image (the figure shows the default settings).

Changes in the position of a control point are reflected directly in the two left-hand columns of the editor and (in Execute on Change mode) in the Image window. The "data range" from the bottom to the top of the color column is the range of actual data values for which image characteristics (e.g., hue) can be specified.

Specifying Colormap Values

You can specify a Colormap value in two ways:

• Directly by manipulating a control point.

• Indirectly through the Add Control Points dialog box.

Figure 9. Colormap Editor for .../example1.net. The four image characteristics controlled by the editor (hue, saturation, value, and opacity) are also listed in Table 1. The numerical range for each is 0.0-1.0. For Hue this range is "r g b r" (red green blue red); the current setting corresponds to the red-green-blue spectrum of the color column to the left. The column furthest left (RGB) displays the red-green-blue color values corresponding to the four settings on the right. Note that each setting is determined by a "line" whose position can be changed by moving the "control point" at one of its ends; the shape of the line can be modified by adding control points (see text). The values 0.0 and 2.5000000 are the minimum and maximum of the data values used in the visual program.

Specifying approximate values:

1. Position the mouse cursor in the middle of the large Value rectangle and double click the left mouse button. Note the changes that result:

   • A new control point appears (turning the vertical line into two line segments) and the Value button is activated.

   • The data value of the new point is displayed in the data range next to the color column (the RGB area, color column, and image show corresponding changes).

2. To move the control point, use the left mouse button to drag it. The RGB area, color column, data value, and image all change accordingly.

3. To return Value to its previous state, double click on the control point.

1. Select Edit in the menu bar of the Colormap Editor and then select Add Control Points in the pull-down menu. A dialog box appears (see Figure 10).

   Figure 10. Add Control Points Dialog Box. This dialog box has two interactors: The first specifies the actual data value for which a corresponding set of Colormap values are to be implemented. The second specifies one of the four Colormap values, such as Hue in this example (see text).
   
   

   
   
   

2. Click on the Saturation rectangle of the Colormap Editor. The label button in the editor is activated (recessed) and the new interactor label in the Add Control Points dialog box changes to "Saturation value (0.0 to 1.0)."

3. Click on the data value displayed in the dialog box, type in the value 1, and press Enter. The new value is displayed as 1.00000.

4. Click on the saturation value displayed in the dialog box, type in the value .28, and press Enter. The new value is displayed as 0.28000.

5. Click on Add in the dialog box: A control point corresponding to the new values in the dialog box appears in the Saturation rectangle of the editor. The RGB area, color column, and image all change accordingly.

Now that you know how to open and execute visual programs and to control the images they generate, you can proceed to Tutorial II, which deals with various techniques for visualizing data.

Additional Notes on Control Points

Displaying Control Point Values By default the Colormap Editor displays the values of all control points. To display the value of an individual point: Select in order: Options in the menu bar of the ColorMap Editor Display Control Point Data Value in the pull-down menu Selected in the pull-down list. Click on the desired control point in the ColorMap Editor (the rectangle containing the control point is automatically activated if it is not already activated). The data value corresponding to the selected control point appears in the data range next to the color column. Repeat the preceding selection procedure, except click on All in the pull-down list (instead of Selected). Data values for all control points in the activated rectangle now appear in the data range. Deleting Control Points You can delete control points one at a time or in groups: To remove control points one at a time (in an activated rectangle), double click on each point to be removed To remove two or more points at a time: Select points by either: Shift-clicking: Press the Shift key and click on each point to be deleted; or Drawing a selection box: Hold down the left mouse button and drag the cursor to generate a "selection box" in the selected rectangle and enlarge it to the desired size. Release the button (the box disappears, but any "boxed" points are selected). Select Edit in the menu bar and then Delete Selected Control Points in the pull-down menu. All selected control points are deleted and the image is updated.