3.7 Visualizing 3-Dimensional Data
The following examples illustrate several ways of visualizing
3-dimensional data.
Isosurfaces
This example uses cloud-water density data for a severe storm.
- Open and execute visual program .../Isosurface3D.net.
The "isovalue" used for generating the isosurface that appears is,
by default, the average of all the data values.
(The default isovalue can be found by selecting Open Message
Window in the Windows pull-down menu.)
- Change the isovalue:
- Open the configuration dialog box for
Isosurface.
- In the value parameter
field, set the value to "0.3."
- Click on OK and reexecute
the visual program.
The new isosurface is significantly smaller.
See Isosurface in IBM Visualization Data Explorer User's Reference.
Slices
Following are a few examples of how to generate and process data
slices.
For 3-dimensional data on any type of grid or for non-orthogonal slices,
use the MapToPlane tool.
If the data set is on a regular grid, use the Slab
tool to take slices along connection elements.
You can use other tools (e.g., AutoColor or
RubberSheet) on data slices just
as you can on any 2-dimensional object.
- Open and execute visual program
.../MapToPlane.net.
The image is a colored plane through a 3-dimensional data
field.
By default, MapToPlane maps onto a plane at the
center of the data.
To change the orientation of this plane:
- Open the configuration dialog box for MapToPlane,
change the value in the normal parameter field to
[1 1 1] and click on OK.
The change of orientation will appear when the program is reexecuted.
- Reexecute the visual program.
MapToPlane performs the necessary interpolation
for a data slice of any orientation in a 3-dimensional field.
See MapToPlane in IBM Visualization Data Explorer User's Reference.
To visualize an orthogonal slice without interpolation, use
Slab:
- Open and execute visual program .../Slab.net.
The image is a translucent isosurface with a colored slice (or slab)
cutting through it.
To visualize a slice through another part of the isosurface:
- Open the configuration dialog box for Slab and
change the position parameter value to "10."
- Click on OK or Apply.
- Reexecute the visual program.
The position of the new slice is changed.
See Slab in IBM Visualization Data Explorer User's Reference.
To create an animation that generates different slices of the data:
- Select Special in the categories palette and
then Sequencer in the tools palette.
- Position the cursor to the right of Slab in the
VPE.
- Open the Slab configuration dialog box.
- Click on the position toggle (unsetting the
parameter value).
The parameter field now reads "(all)" and the third
input tab on the Slab icon (counting from
the left) projects outward from the icon (instead of
into it).
- Click on OK.
- Connect the output tab of Sequencer to this
third input tab (i.e., "position") of
Slab.
- Double click on the Sequencer icon to display
the Sequence Control panel.
- Click on the frame button (...) to
display the Frame Control panel.
- Reset the limits:
- Click on the min field, type "0," and
press Enter.
- Click on the max field, type "20," and
press Enter.
- Click on the Forward (>) button to play the sequence.
See "Using the Sequencer" in this Guide
and Sequencer
in IBM Visualization Data Explorer User's Reference.
Streamlines
The Streamline module traces the path of a massless
particle through a static velocity field.
- Open and execute visual program
.../Streamlines3D.net.
The image is a translucent isosurface with a single streamline starting
from the point [25000 5000 25000] (as specified in the
Streamline module's
configuration dialog box).
This streamline can be transformed into a ribbon:
- Select Annotation in the categories palette and
then Ribbon in the tools palette.
- Position the Ribbon icon below
Streamline in the VPE
canvas.
- Disconnect Streamline output from
Collect input and reconnect it
to Ribbon input.
- Connect Ribbon output to
Collect input.
- Reexecute the visual program.
The streamline changes to a ribbon.
If you want the twist of the ribbon to represent the vorticity of the
wind field:
- Open the Streamline configuration
dialog box.
- Change the flag parameter value from "(input
dependent)" to "1" and click on OK.
Streamline computes the degree of twist from the
vorticity of the wind field.
- Reexecute the visual program.
The twist is greater in regions of higher wind vorticity.
To make the color of the ribbon correspond to wind velocity:
- Select Transformation and then
AutoColor in the palettes.
- Position the AutoColor icon between
Ribbon and Collect
in the VPE canvas.
- Disconnect the Ribbon output from the
Collect input and reconnect
it to the first (leftmost) input of
AutoColor.
Note: Both input tabs can accept a connection, but the
semi-highlighting
indicates required input (i.e., the module cannot function
without it).
- Connect the first (leftmost) output of AutoColor
to the available input of Collect.
- Reexecute the visual program.
Note the variation of color in the ribbon.
See Ribbon and Streamline in IBM Visualization Data Explorer User's
Reference.
3-D Scalar Glyphs
Scalar glyphs can represent 3-dimensional as well as 2-dimensional
data.
- Open and execute visual program
.../AutoGlyph3DScalar.net.
The spherical glyphs on the isosurface represent a subset of the
data elements.
- To visualize the entire data set:
- Disconnect the Map output from
AutoGlyph.
- Connect the output of the left-hand Import
module to the first ("data") input tab of
AutoGlyph.
- Reexecute the visual program.
The number of glyphs is greatly increased.
You can also create your own glyphs (both scalar and vector).
For example:
3-D Vector Glyphs
Vector glyphs can represent 3-dimensional as well as 2-dimensional
data.
- Open and execute visual program
.../AutoGlyph3DVector.net.
The image is a set of 3-dimensional arrow glyphs on an isosurface.
- To visualize the entire data set:
- Disconnect Map output from
AutoGlyph.
- Connect the output of the left-hand Import
module to the first ("data") input tab of
AutoGlyph.
- Reexecute the visual program.
The number of glyphs is greatly increased.
Volume Rendering
Volume rendering is a technique for using color and opacity to visualize
the data in a 3-dimensional data set.
(In contrast, surface techniques use tools like
Isosurface and
MapToPlane to display a 2-dimensional surface,
although in 3-dimensional space.)
The following are some simple examples.
- Open and execute visual program .../VolumeRendering.net.
As the network in the canvas shows, the color of the volume is
determined by AutoColor.
The data set contains relatively few high values (red) and relatively
many low values (blue).
No structure is apparent in the image.
- Select Transformation and then
Equalize in the palettes.
- Position the Equalize icon between
Import and
AutoColorin the VPE canvas.
- Disconnect Import output from
AutoColor input and reconnect
it to the first input tab ("data") of
Equalize.
- Connect Equalize output to the first input tab
("data") of AutoColor.
- Reexecute the visual program.
Equalize redistributes the data values more or less
uniformly between the minimum and maximum of the data.
Although the resulting image is somewhat diffuse, the structure of the
data (the electron density of an imide molecule) is now visible.
AutoColor parameters can be used to add definition
to the structure.
- Delete the Equalize module: Click on the icon
and select Delete in the
Edit pull-down menu.
The connections to Import and
AutoColor are automatically
deleted along with the icon.
- Reconnect the Import output to the first input
tab ("data") of AutoColor.
- Open the AutoColor configuration dialog box.
- Set the value of the min parameter to ".1"
and click on OK.
- Reexecute the visual program.
All data values smaller than 0.1 are rendered invisible (black).
The image is much darker, but still visible.
- To increase the visibility of the data, increase the value of the
intensity parameter in the
AutoColor configuration
dialog box to "5."
- Click on OK and
reexecute the visual program.
The structure of image is now fairly distinct.
A color map gives you much greater control over the appearance of the
image:
- Disconnect AutoColor from
Image and connect the
Color output to the
Image input.
- Reexecute the visual program.
- Bring up the Colormap Editor by double clicking on the
Colormap icon.
The color-bar, Hue, and Opacity settings are clearly
reflected in the image: regions of low data
values (green) and smaller regions of
higher data values (red).
All other data values have been rendered invisible.
Note: To make a region or volume invisible, it is necessary to set
both its intrinsic opacity and its color value
to zero.
The reason is that the volume rendering model assumes that regions
emit light as well as absorb it.
So even if its opacity is zero (no absorption), a region will still emit
light unless its color is black ([0 0 0]).
It is interesting to contrast the volume rendering of previous images
with a surface technique.
For example:
- Disconnect Color from
Image
and connect the Isosurface output to the
Image input.
- Reexecute the visual program.
The resulting image is an isosurface representation of the structure
of an imide molecule.
You can also combine surface techniques with volume rendering.
For example:
- Select Structuring and then
Collect in the palettes.
- Position the Collect icon above
Image in the VPE canvas.
- Disconnect Isosurface from
Image.
- Connect the first output tab ("mapped") of
AutoColor
to either of the Collect input tabs.
- Connect the Isosurface output to the other
Collect input tab.
- Connect the Collect output to the
Image input.
- Reexecute the visual program.
The result is a combination of the volume-rendering and isosurface
images of the imide molecule.
- To make the isosurfaces translucent, insert a new
Color module (from the
Transformation
category) into the network
between Isosurface and
Collect.
(Use the first, or "input," tab of the Color
icon.)
- Open the Color configuration dialog box and set
the opacity parameter to ".3."
(You can try other values as well.)
- Click on OK and reexecute the visual program.
The isosurfaces are now translucent.
