SAS/SPECTRAVIEW Software User's Guide |
An isosurface produces a three-dimensional surface by connecting
all the data points with one response value. That is, the isosurface lets
you see all locations in the volume grid when the response values are equal.
An isosurface is particularly useful in viewing scientific data and physical
properties such as temperature, density, and stress.
You must specify the response value to be displayed
by the isosurface using the response histogram. The value shown corresponds
to the lower histogram level.
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Isolating a Response Value |
With the response histogram, you specify the response
value for an isosurface. The response histogram, which appears at the bottom
left of the interface when you request a point cloud or an isosurface, displays
the frequency distribution of data points that share the same response value.
The histogram may also include software-interpolated values between the actual
response values, which can be used to generate an isosurface.
Response Histogram to Specify Isosurface Value
There are actually two histograms:
- The upper one represents all the response values
in the data set. The positions of the lines are the minimum and maximum response
values.
- The lower one magnifies the portion of the data
that lies between the two lines. The histogram stacks are larger or smaller
relative to all the data between the lines. As you move the lines, you alter
the span of values being compared to each other, so the stacks in the lower
histogram change.
Flat histogram stacks do not necessarily indicate an
absence of response data at that value. When you have a complete grid, the
flat places may simply indicate much fewer values compared to the frequency
of values represented by adjacent stacks. When you have only a few responses
and they are widely separated, the values interpolated between them by the
software may produce a flat stretch in the histogram.
- Select [Tools], [Planes],
then [Isosurface].
- To specify the response value, use the left mouse
button and drag the histogram's left line to the desired value. The default
position of the left line is the minimum response value, which cannot be used
to generate an isosurface. (The right line has no effect on an isosurface
specification.)
- Render the isosurface by selecting:
- [W/ depth sort]
- displays the isosurface with depth sorting
by sorting the planes front-to-back so that the image appears more realistically
three-dimensional, for example, when moving planes through the volume grid.
This method takes more time.
- [W/o depth sort]
- displays the isosurface without depth sorting,
which is a faster, but less realistic method. It is recommended that
you use this method when animating an isosurface with a BY variable to produce
faster animation.
- [Off]
- turns off the displayed isosurface.
By default, the isosurface is drawn in the color shown
in the histogram for the selected response value.
- To assign a different color to the isosurface,
select [Palette], [Isosurface], then [User-defined]. Adjust the RGB sliders. As you move the sliders, the
current color appears in a square at the left, and the isosurface changes
color in the Volume window. You can also
select a color chip, located below the RGB sliders. (To return to the
response value color, select [Response level].)
Isosurface
Note that you can
specify a different response
value when the isosurface is turned on or when it is turned off. However,
if you have a large amount of response data, it may be faster to turn off
the isosurface, then adjust the histogram.
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Effect of a BY Variable on an Isosurface |
For an
isosurface with a BY variable specification, you can request
a specific response value but not see the isosurface display. This is because
the response value you selected is not contained in the data associated with
the current BY value. (The histogram shows all responses, in ascending order,
regardless of the value of the BY variable.)
To see the isosurface that was generated, use [Auto BY] to search for the appropriate BY value. Because the
response
value may be valid for more than one x,y,z location over time, an isosurface
may be generated for more than one BY value. When the applicable BY value(s)
is current, the isosurface is clearly visible.
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.