IVOLUME

The IVOLUME procedure creates an iTool and associated user interface (UI) configured to display and manipulate volume data.

This routine is written in the IDL language. Its source code can be found in the file ivolume.pro in the lib/itools subdirectory of the IDL distribution.

Syntax

iTool Common Keywords: [, DIMENSIONS=[x, y]] [, IDENTIFIER=variable] [, LOCATION=[x, y]] [, NAME=string] [, OVERPLOT=iToolID] [, TITLE=string] [, VIEW_GRID=[columns, rows]] [, /VIEW_NEXT] [. VIEW_NUMBER=integer] [, {X | Y | Z}RANGE=[min, max]]

iTool Volume Keywords: [, /AUTO_RENDER] [, RENDER_EXTENTS={0 | 1 | 2}] [, RENDER_QUALITY={1 | 2}] [, SUBVOLUME=[xmin, ymin, zmin, xmax, ymax, zmax]] [, VOLUME_DIMENSIONS=[width, height, depth]] [, VOLUME_LOCATION=[x, y, z]]

Volume Object Keywords: [, AMBIENT=RGB vector] [, BOUNDS=[xmin, ymin, zmin, xmax, ymax, zmax]] [, CLIP_PLANES=array] [, COMPOSITE_FUNCTION={0 | 1 | 2 | 3}] [, CUTTING_PLANES=array] [, DEPTH_CUE=[zbright, zdim]] [, /HIDE] [, HINTS={0 | 1 | 2 | 3}] [, /INTERPOLATE] [, /LIGHTING_MODEL] [, OPACITY_TABLE0=byte array of 256 elements] [, OPACITY_TABLE1=byte array of 256 elements] [, RENDER_STEP=[x, y, z]] [, RGB_TABLE0=byte array of 256 by 3 or 3 by 256 elements] [, RGB_TABLE1=byte array of 256 by 3 or 3 by 256 elements] [, /TWO_SIDED] [, /ZBUFFER] [, ZERO_OPACITY_SKIP={0 | 1}]

Axis Object Keywords: [, {X | Y | Z}GRIDSTYLE={0 | 1 | 2 | 3 | 4 | 5 | 6}] [, {X | Y | Z}MAJOR=integer] [, {X | Y | Z}MINOR=integer] [, {X | Y | Z}SUBTICKLEN=ratio] [, {X | Y | Z}TEXT_COLOR=RGB vector] [, {X | Y | Z}TICKFONT_INDEX={0 | 1 | 2 | 3 | 4}] [, {X | Y | Z}TICKFONT_SIZE=integer] [, {X | Y | Z}TICKFONT_STYLE={0 | 1 | 2 | 3}] [, {X | Y | Z}TICKFORMAT=string or string array] [, {X | Y | Z}TICKINTERVAL=value] [, {X | Y | Z}TICKLAYOUT={0 | 1 | 2}] [, {X | Y | Z}TICKLEN=value] [, {X | Y | Z}TICKNAME=string array] [, {X | Y | Z}TICKUNITS=string] [, {X | Y | Z}TICKVALUES=vector] [, {X | Y | Z}TITLE=string]

Arguments

Vol0, Vol1, Vol2, Vol3

A three-dimensional array of any numeric type containing volume data. Arrays of strings, structures, object references, and pointers are not allowed. If more than one volume is specified, they must all have the same dimensions.

The number of volumes present and the value of the COMPOSITE_FUNCTION keyword determine how the volume data is rendered by the iVolume tool. The number of volume arguments determine how the src and srcalpha values for the COMPOSITE_FUNCTION are computed:

If Vol₀ is the only argument present, the values of src and srcalpha are taken directly from the RGB and OPACITY tables, as indexed by each volume data sample:

src = RGB_TABLE0[VOL0] 
srcalpha = OPACITY_TABLE0[VOL0]

If Vol₀ and Vol₁ are the only arguments present, the two volumes are blended together using independent tables:

src = (RGB_TABLE0[VOL0]*RGB_TABLE1[VOL1])/256 
srcalpha = (OPACITY_TABLE0[VOL0]*OPACITY_TABLE1[VOL1])/256

If all the arguments are present, Vol₀ indexes the red channel of RGB_TABLE0, Vol₁ indexes the green channel of RGB_TABLE0, and Vol₂ indexes the blue channel of RGB_TABLE0. The Vol₃ argument indexes OPACITY_TABLE0:

src = (RGB_TABLE[VOL0, 0], RGB_TABLE[VOL1, 1], $ 
   RGB_TABLE[VOL2, 2])/256 
srcalpha = (OPACITY_TABLE0[VOL3])/256.

Keywords

AMBIENT

Use this keyword to set the color and intensity of the volume's base ambient lighting. Color is specified as an RGB vector. The default is [255, 255, 255]. AMBIENT is applicable only when LIGHTING_MODEL is set.

AUTO_RENDER

Set this keyword to 1 to always render the volume. The default is to not render the volume each time the tool window is drawn.

BOUNDS

Set this keyword to a six-element vector of the form [x_min, y_min, z_min, x_max, y_max, z_max], which represents the sub-volume to be rendered. This keyword is the same as the SUBVOLUME keyword.

CLIP_PLANES

Set this keyword to an array of dimensions [4, N] specifying the coefficients of the clipping planes to be applied to this object. The four coefficients for each clipping plane are of the form [A, B, C, D], where Ax + By + Cz + D = 0. Portions of this object that fall in the half space Ax + By + Cz + D > 0 will be clipped. By default, the value of this keyword is a scalar (-1) indicating that no clipping planes are to be applied.

COMPOSITE_FUNCTION

The composite function determines the value of a pixel on the viewing plane by analyzing the voxels falling along the corresponding ray, according to one of the following compositing functions:

0 = Alpha (default): Alpha-blending. The recursive equation

dest' = src * srcalpha + dest * (1 - srcalpha)

is used to compute the final pixel color.

1 = MIP: Maximum intensity projection. The value of each pixel on the viewing plane is set to the brightest voxel, as determined by its opacity. The most opaque voxel's color appropriation is then reflected by the pixel on the viewing plane.

2 = Alpha sum: Alpha-blending. The recursive equation

dest' = src + dest * (1 - srcalpha)

is used to compute the final pixel color. This equation assumes that the color tables have been pre-multiplied by the opacity tables. The accumulated values can be no greater than 255.

3 = Average: Average-intensity projection. The resulting image is the average of all voxels along the corresponding ray.

CUTTING_PLANES

Set this keyword to a floating-point array with dimensions (4, n) specifying the coefficients of n cutting planes. The cutting plane coefficients are in the form {{n_x, n_y, n_z, D}, ...} where (n_x)X+(n_y)Y+(n_z)Z+ D > 0, and (X, Y, Z) are the voxel coordinates. To clear the cutting planes, set this property to any scalar value (e.g. CUTTING_PLANES = 0). By default, no cutting planes are defined.

DEPTH_CUE

Set this keyword to a two-element floating-point array [zbright, zdim] specifying the near and far Z planes between which depth cueing is in effect.

Depth cueing causes an object to appear to fade into the background color of the view object with changes in depth. If the depth of an object is further than zdim (that is, if the object's location in the Z direction is farther from the origin than the value specified by zdim), the object will be painted in the background color.

Similarly, if the object is closer than the value of zbright, the object will appear in its "normal" color. Anywhere in-between, the object will be a blend of the background color and the object color. For example, if the DEPTH_CUE property is set to [-1, 1], an object at the depth of 0.0 will appear as a 50% blend of the object color and the view color.

The relationship between Z_bright and Z_dim determines the result of the rendering:

Z_bright < Z_dim: Rendering darkens with depth.

Z_bright > Z_dim: Rendering brightens with depth.

Z_bright = Z_dim: Disables depth cueing.

You can disable depth cueing by setting z_bright = z_dim. The default is [0.0, 0.0].

DIMENSIONS

Set this keyword to a two-element vector of the form [width, height] to specify the dimensions of the drawing area of the specific tool in device units. The minimum width of the window correlates to the width of the menubar. The minimum window height is 100 pixels.

HIDE

Set this keyword to a boolean value indicating whether the volume should be drawn:

0 = Draw graphic (the default)

1 = Do not draw graphic

HINTS

0 = Disables all acceleration hints (default).

1 = Enables Euclidean distance map (EDM) acceleration. This option generates a volume map containing the distance from any voxel to the nearest non-zero opacity voxel. The map is used to speed ray casting by allowing the ray to jump over open spaces. It is most useful with sparse volumes. After setting the EDM hint, the draw operation generates the volume map; this process can take some time. Subsequent draw operations will reuse the generated map and may be much faster, depending on the volume's sparseness. A new map is not automatically generated to match changes in opacity tables or volume data (for performance reasons). The user may force recomputation of the EDM map by setting the HINTS property to 1 again.

2 = Enables the use of multiple CPUs for volume rendering if the platforms used support such use. If HINTS is set to 2, IDL will use all the available (up to 8) CPUs to render portions of the volume in parallel.

3 = Selects the two acceleration options described above.

IDENTIFIER

Set this keyword to a named IDL variable that will contain the iToolID for the created tool. This value can then be used to reference this tool during overplotting operations or command-line-based tool management operations.

INTERPOLATE

Set this keyword to indicate that trilinear interpolation is to be used to determine the data value for each step on a ray. Setting this keyword improves the quality of images produced, at the cost of more computing time. especially when the volume has low resolution with respect to the size of the viewing plane. Nearest neighbor sampling is used by default.

LIGHTING_MODEL

Set this keyword to use the current lighting model during rendering in conjunction with a local gradient evaluation.

LOCATION

Set this keyword to a two-element vector of the form [x, y] to specify the location of the upper left-hand corner of the tool relative to the display screen, in device units.

NAME

Set this keyword to a string to specify the name for this particular tool. The name is used for tool-related display purposes only-as the root of the hierarchy shown in the Tool Browser, for example.

OPACITY_TABLE0

Set this keyword to a 256-element byte array to specify an opacity table for Vol₀ if Vol₀ or Vol₀ and Vol₁ are present. If all the volume arguments are present, this keyword represents the opacity of the resulting RGBA volume. A value of 0 indicates complete transparency and a value of 255 indicates complete opacity. The default table is a linear ramp.

OPACITY_TABLE1

Set this keyword to a 256-element byte array to specify an opacity table for Vol₁ when Vol₀ and Vol₁ are present. A value of 0 indicates complete transparency and a value of 255 indicates complete opacity. The default table is a linear ramp.

OVERPLOT

Set this keyword to an iToolID to direct the graphical output of the particular tool to the tool specified by the provided iToolID.

Set this keyword to 1 (one) to place the graphical output for the command in the current tool. If no current tool exists, a new tool is created.

RENDER_EXTENTS

Set this keyword to draw a boundary around the rendered volume. The default (RENDER_EXTENTS = 2) is to draw a translucent boundary box. Possible values for this keyword are:

0 = Do not draw anything around the volume.

1 = Draw a wireframe around the volume.

2 = Draw a translucent box around the volume

RENDER_STEP

Set this keyword to a three element vector of the form [x, y, z] to specify the stepping factor through the voxel matrix. This keyword is only valid if render quality is set to high (RENDER_QUALITY = 2). The default render step is [1, 1, 1].

RENDER_QUALITY

Set this keyword to determine the quality of the rendered volume. The default (RENDER_QUALITY = 1) is low quality. Possible values for this keyword are:

1 = Low - Renders volume with a stack of two-dimensional texture maps.

2 = High - Use ray-casting rendering, see the COMPOSITE_FUNCTION for more details.

RGB_TABLE0

Set this keyword to a 3 by 256 or 256 by 3 byte array of RGB color values to specify a color table for Vol₀ if Vol₀ or Vol₀ and Vol₁ are present. If all the arguments are present, this keyword represents the RGB color values of all of these volumes. The default is a linear ramp

RGB_TABLE1

Set this keyword to a 3 by 256 or 256 by 3 byte array of RGB color values to specify a color table for Vol₁ when Vol₀ and Vol₁ are present. The default is a linear ramp.

SUBVOLUME

Set this keyword to a six-element vector of the form [x_min, y_min, z_min, x_max, y_max, z_max], which represents the sub-volume to be rendered. This keyword is the same as the BOUNDS keyword.

TITLE

Set this keyword to a string to specify the title for this particular tool. The title is displayed in the title bar of the tool.

TWO_SIDED

Set this keyword to force the lighting model to use a two-sided voxel gradient. The two-sided gradient is different from the one-sided gradient (default) in that the absolute value of the inner product of the light direction and the surface gradient is used instead of clamping to 0.0 for negative values.

VIEW_GRID

Set this keyword to a two-element vector of the form [columns, rows] to specify the view layout within the new tool. This keyword is only used if a new tool is being created (for example, if OVERPLOT, VIEW_NEXT, or VIEW_NUMBER are specified then VIEW_GRID is ignored).

VIEW_NEXT

Set this keyword to change the view selection to the next view following the currently-selected view before issuing any graphical commands. If the currently-selected view is the last one in the layout, then /VIEW_NEXT will cause the first view in the layout to become selected. This keyword is ignored if no current tool exists.

VIEW_NUMBER

Set this keyword to change the currently-selected view to the view specified by the VIEW_NUMBER before issuing any graphical commands. The view number starts at 1, and corresponds to the position of the view within the graphics container (not necessarily the position on the screen). This keyword is ignored if no current tool exists.

VOLUME_DIMENSIONS

A 3-element vector specifying the volume dimensions in terms of user data units. For example, specifying [0.1, 0.1, 0.1] would cause the volume to be rendered into a region that is 0.1 data units long on each side of the volume cube. If this parameter is not specified, the volume is rendered into a region the same size as the number of samples, with an origin of [0, 0, 0]. In this case, a volume with sample size of [20, 25, 20] would render into the region [0:19, 0:24, 0:19] in user data units. Use the VOLUME_LOCATION keyword to specify a different origin.

VOLUME_LOCATION

A 3-element vector specifying the volume location in user data units. Use this keyword to render the volume so that the first sample voxel appears at the specified location, instead of at [0, 0, 0], the default. Specify the location in terms of coordinates after the application of the VOLUME_DIMENSIONS values. For example, if the value of the VOLUME_DIMENSIONS keyword is [0.1, 0.1, 0.1] and you want the volume to be centered at the origin, set the VOLUME_LOCATION keyword to [-0.05, -0.05, -0.05].

[XYZ]MAJOR

Set this keyword to an integer representing the number of major tick marks. The default is -1, specifying that IDL will compute the number of tickmarks. Setting MAJOR equal to zero suppresses major tickmarks entirely.

[XYZ]MINOR

Set this keyword to an integer representing the number of minor tick marks. The default is -1, specifying that IDL will compute the number of tickmarks. Setting MINOR equal to zero suppresses minor tickmarks entirely.

[XYZ]RANGE

Set this keyword to the desired data range of the axis, a 2-element vector. The first element is the axis minimum, and the second is the maximum.

[XYZ]SUBTICKLEN

Set this keyword to a floating-point scale ratio specifying the length of minor tick marks relative to the length of major tick marks. The default is 0.5, specifying that the minor tick mark is one-half the length of the major tick mark.

[XYZ]TEXT_COLOR

Set this keyword to an RGB value specifying the color for the axis text. The default value is [0, 0, 0] (black).

[XYZ]TICKFONT_INDEX

Set this keyword equal to one of the following integers, which represent the type of font to be used for the axis text:

0 = Helvetica

1 = Courier

2 = Times

3 = Symbol

4 = Hershey

[XYZ]TICKFONT_SIZE

Set this keyword to an integer representing the point size of the font used for the axis text. The default is 12.0 points.

[XYZ]TICKFONT_STYLE

Set this keyword equal to one of the following integers, which represent the style of font to be used for the axis text:

0 = Normal

1 = Bold

2 = Italic

3 = Bold Italic

[XYZ]TICKFORMAT

Set this keyword to a string, or an array of strings, in which each string represents a format string or the name of a function to be used to format the tick mark labels. If an array is provided, each string corresponds to a level of the axis. The TICKUNITS keyword determines the number of levels for an axis.

If the string begins with an open parenthesis, it is treated as a standard format string. See Format Codes.

If the string does not begin with an open parenthesis, it is interpreted as the name of a callback function to be used to generate tick mark labels.

If TICKUNITS are not specified:

The callback function is called with three parameters: Axis, Index, and Value, where:

Axis is the axis number: 0 for X axis, 1 for Y axis, 2 for Z axis

Index is the tick mark index (indices start at 0)

Value is the data value at the tick mark (a double-precision floating point value)

If TICKUNITS are specified:

The callback function is called with four parameters: Axis, Index, Value, and Level, where:

Axis, Index, and Value are the same as described above.

Level is the index of the axis level for the current tick value to be labeled. (Level indices start at 0.)

Used with the LABEL_DATE function, this property can easily create axes with date/time labels.

[XYZ]TICKINTERVAL

Set this keyword to a floating-point scalar indicating the interval between major tick marks for the first axis level. The default value is computed according to the axis [XYZ]RANGE and the number of major tick marks ([XYZ]MAJOR). The value of this keyword takes precedence over the value set for the [XYZ]MAJOR keyword.

For example, if TICKUNITS = ['S', 'H', 'D'], and TICKINTERVAL = 30, then the interval between major ticks for the first axis level will be 30 seconds.

[XYZ]TICKLAYOUT

Set this keyword to integer scalar that indicates the tick layout style to be used to draw each level of the axis.

0 = The axis line, major tick marks and tick labels are all included. Minor tick marks only appear on the first level of the axis. This is the default tick layout style.

1 = Only the labels for the major tick marks are drawn. The axis line, major tick marks, and minor tick marks are omitted.

2 = Each major tick interval is outlined by a box. The tick labels are positioned within that box (left-aligned). For the first axis level only, the major and minor tick marks will also be drawn.

[XYZ]TICKLEN

Set this keyword to a floating-point value that specifies the length of each major tick mark, measured in data units. The recommended, and default, tick mark length is 0.2. IDL converts, maintains, and returns this data as double-precision floating-point.

[XYZ]TICKNAME

Set this keyword to a string array of up to 30 elements that controls the annotation of each tick mark.

[XYZ]TICKUNITS

Set this keyword to a string (or a vector of strings) indicating the units to be used for axis tick labeling. If more than one unit is provided, the axis will be drawn in multiple levels, one level per unit.

The order in which the strings appear in the vector determines the order in which the corresponding unit levels will be drawn. The first string corresponds to the first level (the level nearest to the primary axis line).

"Numeric"

"Years"

"Months"

"Days"

"Hours"

"Minutes"

"Seconds"

"Time" - Use this value to indicate that the tick values are time values; IDL will determine the appropriate time intervals and tick label formats based upon the range of values covered by the axis.

""- Use the empty string to indicate that no tick units are being explicitly set. This implies that a single axis level will be drawn using the "Numeric" unit. This is the default setting.

If any of the time units are utilized, then the tick values are interpreted as Julian date/time values. Note that the singular form of each of the time value strings is also acceptable (e.g, TICKUNITS = 'Day' is equivalent to TICKUNITS = 'Days').

[XYZ]TICKVALUES

Set this keyword to a floating-point vector of data values representing the values at each tick mark. If TICKVALUES is set to 0, the default, IDL computes the tick values based on the axis range and the number of major ticks. IDL converts, maintains, and returns this data as double-precision floating-point.

[XYZ]TITLE

ZBUFFER

Set this keyword to clip the rendering to the current Z-buffer and then update the buffer.

ZERO_OPACITY_SKIP

Set this keyword to skip voxels with an opacity of 0. This keyword can increase the output contrast of MIP (MAXIMUM_INTENSITY) projections by allowing the background to show through. If this keyword is set, voxels with an opacity of zero will not modify the Z-buffer. The default (not setting the keyword) continues to render voxels with an opacity of zero.

Examples

In the IDL Intelligent Tools system, data can be imported from the IDL Command Line (as described in Example 1), or data can be imported via the File menu in the iTool window (as described in Examples 2 and 3). For detailed information on importing data via the iTool file menu, refer to Data Import Methods.

Example 1

This example shows how to use the IDL Command Line to bring data into the iVolume tool.

Derive an interval volume by selecting Operations ® Volume ® Interval Volume. In the Interval Volume Value Selector dialog, change the minimum value to 0.2 and the Decimate: % of original surface slider to 20, then click OK.

Example 2

This example shows how to use the iTool File ® Open command to load binary data into the iVolume tool.

Select File ® Open to display the Open dialog, then browse to find head.dat in the examples/data directory in the IDL distribution, and click Open.

In the Binary Template dialog, click New Field, and enter the following information in the New Field dialog:

Field Name: data (or a name of your choosing)

Type: Byte (unsigned 8-bits)

Number of Dimensions: 3

1st Dimension Size: 80

2nd Dimension Size: 100

3rd Dimension Size: 57

Click OK to close the New Field dialog and the Binary Template dialog, and the image is displayed.

Select Operations ® Volume ® Isosurface, and insert an isosurface with a value of 60, decimated to 20% of the original surface.

Example 3

This example shows how to use the File ® Import command to load binary data into the iVolume tool.

At Step 1, select From a File and click Next>>.

At Step 2, under File Name:, browse to find jet.dat in the examples/data directory in the IDL distribution, and click Next>>.

At Step 3, select Volume and click Finish.

The Binary Template wizard is displayed. In the Binary Template, change File's byte ordering to Little Endian. Then, click New Field, and enter the following information in the New Field dialog:

Field Name: data (or a name of your choosing)

Type: Byte (unsigned 8-bits)

Number of Dimensions: 3

1st Dimension Size: 81

2nd Dimension Size: 40

3rd Dimension Size: 101

Click OK to close the New Field dialog and the Binary Template dialog, and the volume is displayed.

Select Operations ® Volume ® Image Plane to display a plane in the x-direction. Double-click on the plane to access its properties through the property sheet. Change the Orientation setting to Z. You can drag the image to see it at different z values by clicking on the edge of the image plane.

Example 4

This example shows how to use a second volume argument to cut away a section of the first volume argument.

Then, create the second volume that will cut away the upper left corner of the head. At the IDL Command Line, enter:

Derive the color and opacity tables for the second volume. At the IDL Command Line, enter:

Example 5

This example shows how to use all the volume arguments to display an RGB (Red, Green, Blue) volume.

First, create the volumes to contain primary colors (black, red, green, blue, yellow, cyan, magenta, and white) in each corner. At the IDL Command Line, enter:

vol0 = BYTARR(32, 32, 32) 
vol1 = BYTARR(32, 32, 32) 
vol2 = BYTARR(32, 32, 32) 
vol3 = BYTARR(32, 32, 32) 
vol0[0:15, *, *] = 255 
vol1[*, 0:15, *] = 255 
vol2[*, *, 0:15] = 255 
vol3[*, *, *] = 128

IVOLUME

Syntax

Arguments

Vol0, Vol1, Vol2, Vol3

Keywords

AMBIENT

AUTO_RENDER

BOUNDS

CLIP_PLANES

COMPOSITE_FUNCTION

CUTTING_PLANES

DEPTH_CUE

DIMENSIONS

HIDE

HINTS

IDENTIFIER

INTERPOLATE

LIGHTING_MODEL

LOCATION

NAME

OPACITY_TABLE0

OPACITY_TABLE1

OVERPLOT

RENDER_EXTENTS

RENDER_STEP

RENDER_QUALITY

RGB_TABLE0

RGB_TABLE1

SUBVOLUME

TITLE

TWO_SIDED

VIEW_GRID

VIEW_NEXT

VIEW_NUMBER

VOLUME_DIMENSIONS

VOLUME_LOCATION

[XYZ]MAJOR

[XYZ]MINOR

[XYZ]RANGE

[XYZ]SUBTICKLEN

[XYZ]TEXT_COLOR

[XYZ]TICKFONT_INDEX

[XYZ]TICKFONT_SIZE

[XYZ]TICKFONT_STYLE

[XYZ]TICKFORMAT

If TICKUNITS are not specified:

If TICKUNITS are specified:

[XYZ]TICKINTERVAL

[XYZ]TICKLAYOUT

[XYZ]TICKLEN

[XYZ]TICKNAME

[XYZ]TICKUNITS

[XYZ]TICKVALUES

[XYZ]TITLE

ZBUFFER

ZERO_OPACITY_SKIP

Examples

Example 1

Example 2

Example 3

Example 4

Example 5

Version History