Overview

There are many operators for processing images, embodied in the ImageVision Library modules listed in Table 3-1 under Process Images. You can display and record these processed images in DisplayImg.

The modules supplied with IRIS Explorer vary widely in function and complexity, providing you with the means to manipulate and process data in many different ways. More information about specific modules is available in these places:

• Table 3-1 lists some of the modules grouped according to function.
• Table 2-1 through Table 2-3 in Chapter 2 list some of the the modules according to the kind of data they accept and deliver; for example, lattice or geometry data.
• The IRIS Explorer Reference Pages list all modules alphabetically and set out the specifications of each one.

Not all the modules listed are available on all systems. The IRIS Explorer Reference Pages indicates the modules available for general distribution.

A selection of modules is listed by function in Table 3-1. (footnote)

Creating Colormaps

When you are looking at large amounts of data, it helps to be able to distinguish significant features easily, and a convenient way to differentiate a range of values is by using color. The GenerateColormap module control panel (see Figure 3-1) lets you select a color space, manipulate the color bands, and send the results to Render, where the visualized data object is colored according to its data values.

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Figure 3-1 The GenerateColormap Module

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GenerateColormap has two input ports, both of which accept the lattice data type, and several input parameters that are connected to widgets on the module control panel. The first input port accepts a colormap, which means you can read a colormap data file that contains preset parameters into the map. The volume map in Chapter 1 provides an example.

The second input port accepts data in the form of a lattice, which means you can feed a lattice into the colormap to set the minimum and maximum limits of the domain. Both these ports are optional.

The output port produces a colormap in the form of a 1D lattice. You can connect GenerateColormap to any module that has a Colormap input port. These include BallStick, Contour, LatToGeom, PyrToGeom, and VolumeToGeom.

You can have several GenerateColormap modules in a map if your X server contains enough entries in its colormap table. See Running the X Server in Appendix A for more information.

Resetting the Color Bands

You change the slope, and hence the value, of a color band in order to adjust the color spectrum in the colormap. In this fashion, you can emphasize certain subsets of your data and block out others. This is easiest to do with the full-scale GenerateColormap control panel (see Figure 3-1).

The control panel has three windows:

• The palette window shows the spectrum of colors currently associated with the data range. The colormap has 256 entries which are spaced uniformly through the range.
• The editing window shows the relationship between the color bands. You can use the RGB (Red/Green/Blue) or HSV (Hue/ Saturation/Value) color systems to create a colormap.
• The scale window shows the range of data values for the map. You can change the minimum and maximum values for the domain by typing new values into the text slots on the dials.

Selecting an Output Mode

Use the Output? option menu to select a mode in which to work. The Build option disables the module temporarily while you edit the color bands. This is useful if you want to experiment without the module constantly firing and sending data to the modules downstream.

The Run option re-enables the module. All changes are reflected in the color palette as you make them, and are simultaneously sent to the next module downstream.

Setting the Domain Limits

Each map processes data with values over a specified range. You can set the limits of the range affected by GenerateColormap by turning the Min Domain and Max Domain dials. Each dial has two text slots that you can use to define the range for minimum values and maximum values.

To change a domain value (min, max, or current), click on the text slot to highlight it and type in the new value, then press < Enter>. The new value appears in the text slot and in the scale window.

Selecting a Color Band

You can edit only one color band at a time. To select a color band:

1. From the Color Space option menu, select RGB or HSV, depending on which system you want to use.
2. From the Color Band option menu, select the color band you want to adjust.
   • In the RGB color space, your options are Red, Green, Blue, and Opacity.
   • In the HSV color space, your options are Hue, Saturation, Value, and Opacity.

Adding and Removing Control Points

You edit color bands by adding control points at intervals along their length and then dragging the points around in the editing window. The points appear as filled boxes (see Figure 3-2).

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Figure 3-2 Adding Control Points to a Color Band

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Use the Edit Mode option menu to add and remove control points. The Insert and Delete options default to Move after every insertion or deletion of a point.

To add a new control point to a color band, select Insert from the Edit Mode option menu and click on the color band at the place where you want the new point. The point is centered between the existing points on that segment of the color band. Move it by dragging on it.

The closer together the points are, the more precise the changes that you can make to the shape of the curve. However, you cannot move a point past the one to its left or right.

To remove an existing control point from a color band, select Delete from the Edit Mode option menu and click on that control point.

You can delete any point except the endpoints.

Using Slope Control Points

Each control point (except the end-points) has two empty squares associated with it, which control the slope of the curve at a given point. They are the derivatives of the curve at that point.

When you select a control point by clicking on it, the slope control points appear on either side (see Figure 3-3). They disappear when you select another point.

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Figure 3-3 Slope Control Points

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If you want to sharpen the curve toward the lower boundary of the window and the position of the slope control point blocks you, simply add another point to the line near the first point and use its derivatives to alter the slope.

Using Custom Colormaps

GenerateColormap creates a rainbow-like colormap when you first launch it. You can use a different colormap as your starting point if you wish.

To read in a custom colormap, first launch a ReadLat module and connect it to the input port of GenerateColormap. Then use the file browser in ReadLat to read in the colormap file. The GenerateColormap module will approximate the input colormap as closely as it can. You can use control points to edit the color curves that it creates.

IRIS Explorer has another module, WaveFormColormap, which uses ramp waves of variable frequency, rather than direct manipulation, to establish a relationship between data values and colors. For more information, refer to WaveFormColormap in the IRIS Explorer Reference Pages.

Creating a Custom Colormap

Saving a Colormap

You can save a colormap to disk by connecting a WriteLat module to GenerateColormap's output port. Then use the file browser to give the saved colormap a filename.

Example 3-1 Manipulating a Colormap

This example illustrates how to generate a colormap for a lattice and alter the relationship between the data values and the color spectrum.

1. Launch these modules from the Module Librarian:

   GenLat, LatToGeom, Render, and GenerateColormap

2. Wire them up as follows:

   GenLat to LatToGeom (Output -- Lattice to Input -- Lattice)

   GenLat to GenerateColormap (Output -- Lattice to Data In -- Lattice (Opt))

   GenerateColormap to LatToGeom (Colormap -- Lattice to Colormap -- Lattice (Opt))

   LatToGeom to Render (Output -- Geometry to Input -- Geometry (Opt))

3. Change the GenLat settings to create a 2D curv full cyl curvilinear lattice with only 1 data variable and change the Output? option on GenerateColorMap to Run. You should have a map that resembles the one in Figure 3-4. To make it more similar, increase the size of the lattice in GenLat. GenerateColormap starts in HSV mode.

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Figure 3-4 A Map using GenerateColormap

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Click on the Output? option menu and select Run. Then do the following and look at the results:

1. Add two points to the red color curve (Hue), three points to the blue (Saturation), and two to the green (Value).
2. Move the points around as far as they will go. See what happens to the objects in Render.
3. Switch from HSV to RGB. Observe how the position of the color curves has changed, even though the color spectrum is still virtually the same.
4. Edit a color band in Build mode, then in Run mode.

Generating a Lattice

The GenLat module (see Figure 3-5) enables you to generate synthetic lattice data for test maps. You can create a large variety of lattices of different sizes, shapes, contents, and representations in order to drive other modules that accept lattices. For example, you can easily verify that a given module performs properly on any type of input lattice. Simply connect GenLat to the module, and then start generating different types and styles of lattices.

GenLat has no input ports and only one output port for the generated lattice. You can connect it to any module that accepts the type of lattice you want to generate.

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Figure 3-5 The GenLat Module

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Setting Lattice Parameters

Controlling Lattice Size

Lattice Coordinates

Data Values

The data values in lattices can be any of the primitive data types (see Using the Lattice Data Type in Chapter 3 of the IRIS Explorer Module Writer's Guide). These include byte, short, long, float, and double.

To set a data type, click on the Data Type option menu and select an option.

Data values are scaled either in a fixed range of zero to 255 or their maximum possible range for the integer types (char, short, or long). However, a range of -1.0 to 1.0 is used for float and double.

To set the data range, click on the Coord Range option menu and select an option.

Using the maximum possible range for the long primitive type can generate very large numbers.

The values of the data can be generated by one of several functions. The default is sines, which fills the data space with the product of sine functions evaluated over a certain number of cycles in each dimension. The other functions are:

• Random data
• Ramps (modulo function)
• Simulated gravity wells

DataVec Length indicates the number of components at each node of the lattice.

Displaying a Lattice

To display lattice data in IRIS Explorer, you can:

• cut a slice using any of the three slicers (see Slicing Volumetric Data)
• create an isosurface with IsosurfaceLat (see Figure 4-15 in Chapter 4)
• create contour lines using Contour (see Figure 4-15)
• create vectors using VectorGen

Since Render accepts only Geometry data, you must wire modules that produce lattice or pyramid data to LatToGeom, VolumeToGeom, or PyrToGeom, which in turn can be connected to Render. You can also send a lattice directly to DisplayImg. Figure 3-4 shows a lattice passed directly to LatToGeom.

Slicing Volumetric Data

There are several ways to do this, depending on the type of data you start with and the results you want to produce. Table 3-2 shows which slicers you can use for each combination of lattice types.

You can use the DataScribe to create a single module which combines all these functions. See Chapter 7 for more information.

You can also use other modules such as CropLat2D and CropLat3D, to view slices of a lattice. See the IRIS Explorer Reference Pages for more information on these modules.

Using OrthoSlice

OrthoSlice cuts along the i, j, and k axes in computational space. For a uniform or perimeter lattice, these correspond to the x, y, and z physical axes. Curvilinear lattices have a more complicated relationship between computational and physical space.

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Figure 3-6 The OrthoSlice Module

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The slice number corresponds to the node number. The slice is taken along the axial plane at that particular node. Selecting slice i corresponds to cutting a slice at node i-1.

Figure 3-7 shows a map that uses OrthoSlice to display part of a lattice. You can use any lattice data. For example, you can replace GenLat with ReadLat and read in an external lattice data file if you wish. A good choice is /usr/explorer/data/lattice/testVol.lat. You can also color the output with a colormap by wiring GenerateColormap to OrthoSlice.

The modules in Figure 3-7 are GenLat, OrthoSlice, LatToGeom, and Render. The slice is taken along the i axis of a half-cylinder.

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Figure 3-7 Slicing a Volume with OrthoSlice

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Using Slice

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Figure 3-8 The Slice Module

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• Use the widgets on TransformGen to angle the slice in any direction you choose.
• Use the Offset dial on the Slice control panel to position the slice plane perpendicular to its axis in the volume. The plane is offset from the center of the volume.
• Use the Resolution slider on the control panel to set the scale for the slice lattice. It determines the number of nodes.

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Figure 3-9 Slice Extended Beyond Lattice Bounds

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Figure 3-10 Slicing a Volume with Slice

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Using ProbeLat

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Figure 3-11 The ProbeLat Module

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It takes slices from a curvilinear lattice in the form of:

• a single planar slice
• a trihedral, which is three mutually perpendicular planes (see Figure 3-12)
• a paddlewheel, which is three planes radiating from a center at 120^o to one another (see Figure 3-12)

The module accepts a transform from TransformGen which sets the orientation of the slice. The slice is output in the form of a pyramid.

You can select the form the probe takes (Probe Type) and the area of the slicing plane (Clip Size) from the ProbeLat control panel.

For pyramids you can use SlicePyr and ClipPyr.

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Figure 3-12 Probe Forms

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Figure 3-13 shows a paddlewheel probe generated by ProbeLat.

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Figure 3-13 Slicing a Volume with ProbeLat

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Generating a Histogram

You can examine data distribution in a lattice by connecting any module that has a lattice output into the Histogram module and generating one or more histograms. The histogram (see Figure 3-14) shows how many times a data value occurs in the input lattice.

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Figure 3-14 The Histogram Module

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The Histogram module has one lattice input port and one lattice output port. The input port accepts any type of input lattice, and the output port produces a count of the input data values in the form of a lattice.

Displaying Histograms

The Histogram control panel has a display window that shows the histogram itself and scale windows that show the domain (horizontal, or x, axis) and range (vertical, or y, axis) of the data values.

The domain changes automatically according to the channel selected. You can override the default limits by entering new values in the Min Domain and Max Domain text slots on the control panel.

Sorting the Data

The Histogram module divides the range of data values in the lattice into a number of equal subranges called buckets. It counts the number of nodes in the lattice whose values lie in each of the buckets and produces a histogram of the counts.

To set the number of subdivisions in the data domain, you can move the Num of Buckets slider, or type in a new value and press <Enter>.

If you define a domain with a narrower spread of values than the actual dataset in a channel, then the out-of-range values are omitted from the histogram if Outliers is set to Omit; all the data points below the minimum value on the scale are put into the first bucket, and all the data points above the maximum are put into the last bucket if Add is specified.

The range of data counts is indicated by the height of each bucket.

Selecting Channels

The option menus let you choose whether you want to generate a histogram for only one data channel of the input lattice, or for all channels. Each channel shows the values for one variable in the input lattice.

To select a data channel, move the Channel slider (this slider is displayed only if more than one channel may be selected from the input lattice). You can also type a number into the Current Value slot at the top of the slider.

To choose between displaying one channel or all channels, click the relevant radio button.

If you select One Channel, a single histogram showing the data distribution in the selected channel is displayed.

If you select All Channels, you see as many separate but overlapping histograms as you have channels. The active histogram is white. It shows the currently selected channel, which is the channel corresponding to the number on the slider. You can change the active histogram by using the slider to select another channel (while in the One Channel mode).

When you select One Channel or All Channels, Histogram produces a 1D output lattice.

When you select Multi-Dimensional, you do not get a display, and the output lattice has a different format. The number of data variables in the input lattice defines the number of dimensions of the output lattice. For example, if the input lattice has three data variables, the output lattice will be 3D.

Each side of the output lattice is divided evenly into the number of buckets defined for the input lattice. The data buckets are formed by dividing the 3D lattice into smaller cubes, each of which contains the data points in that section of the total volume.

Example 3-2 Generating Histograms

This example illustrates how you can generate a histogram for each data channel of GenerateColormap using Histogram.

1. Launch a GenerateColormap module and a Histogram module from the Module Librarian.
2. Connect the GenerateColormap module's Colormap - - Lattice output port to Histogram's data input port.

   When GenerateColormap passes data to Histogram, you can create a histogram for the data coming in from a single channel, or for the data coming in from all four of GenerateColormap's channels.

3. Use the slider to change the selected channel and see what happens.

Displaying Images

At times, you may find it useful to display an image, as opposed to a geometric object, on the screen, perhaps to see what the original image data looks like before it is processed through a map, or so that you can compare two images, or create a composite image from two separate images.

The DisplayImg module (see Figure 3-15) accepts image data in the form of a 2D lattice, either black and white or in color.

You can display several images in the DisplayImg window at any given time. Simply wire as many modules as you require into the input port of DisplayImg.

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Figure 3-15 An Image in the DisplayImg Module

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As each module upstream from DisplayImg fires, an image appears in the DisplayImg window. The image is placed at the bottom left-hand corner of the window, and each subsequent image is stacked on top of it.

• To see the images underneath, you can change the stacking position of the images with the <PgUp> and <PgDn> keys on the numerical keypad (not the <Page Up> and <Page Down> keys to the left of the numbers). Place the cursor over the image of interest.
• To move the top image to another area of the window, click on it with the left mouse button and drag it to a new position. You can move all images around in the window by using this method.
• To return an image to its original position, place the cursor on the image and press the <Home> key on the numerical keypad. If the window contains several images and the cursor is not on any one, they all return to the lower left corner.
• To increase or decrease the size of an image by using the zoom widget. Click on the image you want to zoom. The slider shows the current zoom factor for that image. As you adjust the slider, the zoom factor changes with the size of the image.

You can photograph the image in the window and send it on to another module to be processed by clicking on the Snap? button. You can arrange several images in the window and Snap? will produce a single composite image that is the same size and shape as the original.

You can also remap the image.

The DisplayImg window should not be obscured by any other windows, or the image will not be properly displayed.

Because the product of DisplayImg is also a lattice, you can send the image to any module that accepts a 2D lattice, through the lattice output port on DisplayImg.

Example 3-3 Comparing Two Images

This example illustrates the use of DisplayImg to compare an image in its original form with the same image after it has been modified.

1. Launch a ReadImg, a BlurImg, and a DisplayImg module in the Map Editor.
2. Connect the output port on ReadImg to the input port on DisplayImg.
3. Wire the output port on ReadImg to the input port on BlurImg by clicking on Connect in the cascade menu.
4. Wire the output port on BlurImg to the input port on DisplayImg.
5. Open the file /usr/explorer/data/image/flowers2.rgb in ReadImg.

   When the module fires, you should have two copies of the image in the DisplayImg window. Use the mouse to position them in the full-scale module window.

6. Turn the dials on the BlurImg module and compare the top image with the bottom one (see Figure 3-16).
7. Replace BlurImg with another image-processing module and see what effect it has on the image.

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Figure 3-16 Example Showing Two Images in DisplayImg

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Visualizing Data

Since IRIS Explorer visualizes numerical data after it has been processed in various ways, the Render module (see Figure 3-17) is naturally a very important part of the process. It is Render that:

• displays the geometric object, which it renders from 3D geometry sent to it by compatible modules, in its window
• provides a wide selection of visual enhancement techniques for studying the object further

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Figure 3-17 The Render Module

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The Render module can accept multiple inputs, and it manages each one separately. Its viewing and editing functions are available only in the full-scale control panel. When the full-scale window is open, the Diminutif window is blanked.

Render has several viewing modes and an edit mode, in which an object can be selected and its attributes altered. The functions and attributes of the Render module are described fully in the IRIS Explorer Reference Pages.

Ports on Render

Modes of Operation

Render has four mutually exclusive viewing modes. The viewing mode is a way of considering how the camera in the scene is moving. The viewing modes are selected from the Edit menu on Render's menu bar. Each one lets you view the scene in the Render window in a slightly different way. You can examine, fly by, or walk by the object, or you can change the viewing plane.

You can zoom in and out, as if looking at the object through a telephoto or wide-angle lens. The object appears closer when you zoom in, although it actually remains the same distance from the camera.

To zoom in or out, hold down the left and middle mouse buttons and move the mouse towards or away from the screen.

Selecting an Object

To select an object, click the left mouse button on it. The object appears surrounded by a red box (see Figure 3-18).

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Figure 3-18 A Selected Object

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Moving an Object

To move the camera view around the center point, that is, to move it in the plane of the screen, hold the middle mouse button down and drag the object.

Using the Pop-up Menu

The Render pop-up menu (see Figure 3-19) appears when you click on the background of the Render window. If you zoom or truck in too far and lose sight of the object, click on the window background with the right mouse button and select View All from the Functions submenu of the pop-up menu.

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Figure 3-19 Render Pop-up Menu

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• To center an object in the window, choose View Selection from the Viewing menu (this item is selectable only if more than one object is currently displayed in Render's window). You need to select an object in the Pick/Edit mode first.
• To restore the original camera angle after you have moved the object around, select Home from the Functions submenu of the pop-up menu.

Using Graphical Shortcuts

The Render module provides several graphical shortcuts for manipulating objects in the Examiner, Navigator, and edit modes. To use the shortcuts, select Decoration from the pop-up menu. A frame containing several widgets appears around the Render window (see Figure 3-20).

The widgets include:

• thumbwheels that control the camera rotation or tilt and trucking motion. They also work in Pick/Edit mode.
• a slider that controls the zoom action.
• eight buttons that correspond to View, Pick/Edit, Help, Home, Set Home, View All, Seek, and Camera Type.

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Figure 3-20 The Render Decorations

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Wireframe Rendering

When you have an opaque object in the Render window, it may be easier to examine or move around in wireframe form. You can draw the object as a wireframe structure (see Figure 3-21) by selecting Draw Style from the Render pop-up menu in either viewing mode, then clicking on wireframe.

This command acts on all the objects in the scene, not just on a selected object.

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Figure 3-21 Wireframe Object in Render

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If you are viewing a complex scene with several objects, it may take a long time to render each frame while moving it. Wireframe rendering is much faster than rendering opaque objects, so you may want the objects to be rendered in wireframe while they are moving and opaque when still.

To draw the objects in wireframe as the camera moves, use the move wireframe option. When you release the mouse button, the objects are again drawn in their original mode.

Editing Object Properties

Objects displayed in Render have a variety of attributes. They include positional properties, such as translation, rotation, and scale, and surface properties, such as color, specularity, and transparency. You can change or edit all these attributes using the Render editors in User Pick Mode.

You edit object attributes by picking the object and then selecting an editor from the Editors menu.

Each editor provides access to various attributes of the object (see Table 3-3).

Using the Material Editor

The Material Editor (see Figure 3-22) lets you change the color and texture of an object in a scene. You can set:

• Ambient intensity: the level of ambient color
• Diffuse intensity: the level of diffuse color
• Specular intensity: the level of specular color
• Emissive intensity: the amount of light the object emits
• Shininess: the amount of surface shininess on the object
• Transparency: the degree of transparency or opacity

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Figure 3-22 The Material Editor

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Use the sliders to set the brightness, or intensity, of each color.

To change the material color itself, click on one of the radio buttons on the Editor. The Color Picker appears and you can edit the ambient, diffuse (usually the same as ambient), specular, and emissive colors in turn. By clicking on the square buttons to the right of the radio buttons, you can select to edit one or more of these colors simultaneously. In this case, a tick mark appears to indicate which colors have been selected for editing. Naturally, in this situation they will all have the same color assigned to them.

For details on how the Color Picker works, refer to Using the Color Editor below.

Using the Color Editor

You can change the color properties of the object material using the Color Editor (see Figure 3-23). Use the Sliders menu to select RGB, HSV, or both. Choose colors from the color wheel. Use the Edit menu to stipulate whether or not the change is immediately reflected in the object. By selecting Manual, you can prevent any color change taking effect on the object until you are ready.

Use the two color squares to test new colors and store the previous one. By clicking on the three arrowed pads beneath the squares, you can switch back and forth between colors.

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Figure 3-23 The Color Editor

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The new color is always on the left and the previous color on the right. You can send the new color to the right square, or the old color to the left square.

The Color Pickers in the other editors work in the same way as the Color Editor, although they affect the color of different items.

Using the Transform Sliders

The Transform sliders (see Figure 3-24) let you rotate, translate, and resize any object that is part of the scene in the Render window. The changes affect only the selected object, not all the objects in the scene. The slider widgets are:

• TRANSLATIONS: changes the position of the object in the scene
• SCALES: changes the relative size of the object in the direction of the three axes (conveniently called x, y, and z). The direction of the axes is defined by the SCALE ORIENTATION widget.
• ROTATIONS: changes the orientation of the object in the scene
• SCALE ORIENTATION: changes the direction of the axes along which the object is scaled
• CENTER: changes the center about which rotations take place

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Figure 3-24 The Transform Sliders

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Next to the slider name in the open slider is a Style button. It offers three different layout styles for the widgets in the slider. To see the different widget layouts, click on Style.

Displaying Transparent Objects

If you want to make an object transparent, use the Transp slider in the Material Editor (see Using the Material Editor). To display the transparent object, you can select Screen Door Transparancy or any of the other sorted transparency widgets on the Viewing menu.

Some workstations do not support sorted transparency. They can only display transparent objects in Screen Door format.

As its name implies, Screen Door Transparency renders objects as meshes that you can see through.

Sorted transparency, also called blended transparency, gives a more accurate rendering of the transparent object, but the scene is drawn more slowly than in Screen Door format.

Changing the Lighting

The Render module has a headlight that is situated in the camera position, which is defined as being just over your left shoulder. The headlight moves with the camera. You can also create point, spot, and directional lights, which remain with the objects in the scene. Thus, if the camera moves left, the lights appear to move to the right. You can have as many as you like on at any given time.

You can change the direction, color, and intensity of each light in the scene by using the Lights menu to toggle lights on and off and to edit their attributes. You can also edit ambient light levels.

If you cannot see the Lights menu on the Render menu bar, just enlarge the Render window to the right.

Changes to the lights affect all the objects in the scene, unlike changes to the transform and material properties, which apply only to the selected object.

Editing a Light

To edit the properties of a light, for example, the headlight, select Headlight from the Lights menu and click on Edit. The Edit window appears (see Figure 3-25), displaying the light you have selected.

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Figure 3-25 Light Editor

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You can also adjust the angle at which the light shines on the object by clicking on the directional arrow and changing its position in the window.

The Edit menu provides access to the Color Picker window for changing the color of the light. The Color Picker works in the same way as the Color Editor.

Manipulating Objects

The Manips menu options let you rotate and translate objects in a scene by attaching one of several manipulators to them. You can use only one type of manipulator at a time, but you can attach it to each of several objects at the same time. You can use these manipulators to reposition the object in the scene. The movement is not as precise as that achieved by using the sliders in the Transform Editor, but it is a more direct manipulation.

To remove a manipulator from an object, click on None (this will surround the object by a red box to indicate it is selected) or select another manipulator from the Manips menu. Click on the background of the Render window to remove a manipulator completely.

Example 3-4 Using the Trackball

The Trackball manipulator (see Figure 3-26) consists of opaque stripes surrounding the object. These stripes are aligned with the local axes of the object.

• To rotate the trackball, place the cursor on the stripes and drag the mouse in the desired direction, with the left mouse button held down. When you release the mouse, the ball continues to spin until you click the left mouse button.
• To rotate the trackball in the direction of a single axis, place the mouse on one of the stripes, then drag it in the direction of the stripe.

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Figure 3-26 The Trackball Manipulator

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If you start the trackball spinning and then move the mouse outside the sphere, the ball continues to spin within the plane of the screen.

You can use the Transform Editor to monitor the object's degree of rotation, as reflected in the rotation slider values.

Constructing Loops

You may sometimes need to go beyond the linear dataflow model of existing IRIS Explorer maps to build maps containing dataflow loops. They are needed, for example, for data interrogation through picking in Render, iteration through data sets using For or a multiple-data set reader, and convergence of a simulation using While.

For example, Figure 3-27 illustrates a loop from Render to QueryLat and back to Render.

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Figure 3-27 A Loop in a Map

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The user picks on an object in Render, which fires and sends the pick coordinates to QueryLat. QueryLat turns the coordinates into text and sends it to Render. When the data arrives back at Render, the loop is terminated. To start the loop again, the user has to make another pick.

The common goal in all loops is to feed data from one phase of an IRIS Explorer computation back around to the next phase of the computation. As in most programming languages, loops in IRIS Explorer are a basic and necessary semantic element. It is also true that looped maps are more complex than linear, or unlooped, maps. This section describes how you can conveniently and correctly employ looped maps in your IRIS Explorer data visualizations.

Defining a Loop

You can create two kinds of loops, While loops and Repeat loops, like the similarly named loops in C. In While loops, a specific condition evaluates to true and then an iteration takes place. This sequence is repeated until the condition evaluates to false.

In Repeat loops, an iteration takes place and a condition is then evaluated. Similarly, the sequence is reiterated until a stopping condition is reached.

Loop Controllers

Loop controllers are identified in the Map Editor by a small square icon, the controller icon, at the centre of the title bar in the mini and micro control panel (see Figure 3-28).

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Figure 3-28 Loop Controller Modules

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You can identify a loop controller module only after it has been launched in the Map Editor; until then, it is indistinguishable from other modules in the Module Librarian.

You can also look at the .mres file in the Module Builder; the Build Options window indicates whether the module is a While or Repeat loop controller, or neither. For example, Figure 3-29 shows the controller status for AnimateCamera, which is a Repeat loop controller module.

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Figure 3-29 Build Options for Loop Controller

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The distinguishing characteristic of a loop controller module is its ability to break its loop. IRIS Explorer has While and Repeat modules whose sole function is to control While and Repeat loops, but other modules can also function as loop controllers. Table 3-4 lists the IRIS Explorer loop controllers

How Loops Work

Other controller modules, like Render, do not really control iteration, but need to be control modules in order to support their normal wiring paradigms, such as picking in the Render--QueryLat map (see Figure 3-27). Render needs to be a Repeat controller so that any module in the loop can start the loop.

Wiring a Loop

When you wire a loop in a map, you must include a loop controller module in the loop. If you try to close a loop without a loop controller, you will get a message saying the connection has failed because there is no controller present.

You can have:

• nested loops:
• multiple loops with a single controller
• multiple controller-capable modules in a single loop (with only one of them selected as the active controller)
• and (hopefully) anything else that makes programming sense

Figure 3-30 shows the wiring of the nested loops within this map. AnimateCamera is the loop controller for the inner loop and sends cameras to Render. For controls the outer loop. The Loop Ended port of AnimateCamera is wired to the Fire port of For, to start the next iteration of this outer loop.

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Figure 3-30 Loop Wiring in AnimateIso Map

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Control Arcs

The special coloring of loop control arcs (see Figure 3-31) can help you understand loops. Each loop has a single control arc, which is adjacent to the loop controller that governs it. The control arc is upstream of a While controller and downstream of a Repeat controller. A control arc is conceptually treated as broken by IRIS Explorer when it is computing which modules lie upstream of one another.

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Figure 3-31 Looping Control Arc

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The special control arc wiring helps to clarify otherwise ambiguous loops, such as the one in Figure 3-32, which shows a symmetrical map with separate While loop controllers for each nested loop. Either While module can control loop 3. You will be able to deduce which module controls loop 3 by reading the controller arcs. You can change which module controls loop 3 by selecting arcs and controller buttons carefully.

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Figure 3-32 Ambiguous Looping Scheme

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Saving Loops

Halting a Loop Iteration

In the Map Editor, you can also use the Break Loop option, which appears only on the module pop-up menu of active loop controllers (see Figure 3-33). It forcibly terminates a looping cycle.

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Figure 3-33 Module Menu on Active Loop Controller

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If your looping map seems to be hogging resources with execution highlighting on, try switching it off before you initiate a loop.

The IL Controller Module

This module is used to create a single executable process from a group of ImageVision Library (IL) modules. The module takes map file information about the constituent modules and their ports and connections, and creates an IL operator for each IL module in the map. It then chains these operators to execute the modules, in effect creating a single executable process from all the alternate module executables.

The IL Controller module sits between the ImageVision Library and IRIS Explorer. It is similar to the dataScribe module that uses a scribe file, except that the IL Controller module uses a map file. There must be both a modulename.map file and an .mres file for the module to function.

To use the IL Controller module, this is the procedure you follow:

1. Create a map from several IL modules.
2. Group the modules in the Group Editor and save the map as a group.
3. Save the grouped map file by using the Save Selected item on the Librarian File menu. You will be prompted to confirm that the map is saved as an imaging process. If you click on OK, then an .mres file is created with the map filename.
4. Open the .mres file in the Map Editor. The map comes in as a regular module and uses the IL Controller module as its alternate executable.