IBM Visualization Data Explorer User's Reference

Isosurface

Category

Realization

Function

Computes isosurfaces and contours.

Syntax

surface = Isosurface(data, value, number, gradient, flag, direction);

Inputs

Name	Type	Default	Description
data	scalar field	none	field from which one or more surfaces are to be derived.
value	scalar or scalar list	data mean	isosurface value or values
number	integer	no default	number of isosurfaces or contours to be computed
gradient	vector field	no default	gradient field
flag	flag	1	0: normals not computed 1: normals computed
direction	integer	-1	orientation of normals

Outputs

Name	Type	Description
surface	field or group	isosurface

Functional Details

This module computes any of the following:

• points (for an input field consisting of lines)
• lines (for a surface input field)
• surfaces (for a volumetric input field).

The module also adds a default color to the output (gray-blue for isosurfaces and yellow for contour lines and points) if the input object is uncolored. If the object is colored, its colors are interpolated in the output object.

A "data" component with the same value as the input value is added to the output field.

data	is the data object for which an isosurface or contour is to be created.
value	is the isovalue or isovalues to be used for computing the isosurface(s) or contour(s). If this parameter is not specified, the module bases it calculations on the value specified by number (see below). If neither parameter is specified, the module uses the arithmetic mean of the data input as a default.
number	is ignored if value has been specified. If that parameter is not specified, the module uses the value of number to compute a set of isosurfaces or contours with the following isovalues: min + delta, min + (2*delta),..., min - delta where delta = (max - min)/(number + 1), and "max" and "min" are the maximum and minimum data values of the input field.
gradient	is the gradient field used to compute normals for shading (see Gradient). If this parameter is not specified, the module adds normals by computing the gradient internally (flag can nullify this behavior; see below). Note: If only one isosurface is to be computed, it is probably more efficient to have module compute the gradient internally. If many are to be generated, it is probably more efficient to compute the gradient of the entire field once, so that the system can use it for every isosurface.
flag	specifies whether normals are to be computed for shading. A setting of 0 (zero) prevents the computation of normals. The default is 1 (one)
direction	specifies whether the normals should point against (0, the default) or with (1) the gradient.

Notes:

1. This module adds an attribute called "Isosurface value," which has as its value the isovalue(s) used. To extract this attribute (e.g., for use in a caption for an image), use the Attribute module.
2. For contour lines, this module adds a "fuzz" attribute so that the line will be rendered slightly in front of a coincident surface (see Display).
3. A surface or contour is considered to be undefined if every point in the input volume or surface, respectively, is equal to value. In such cases, the module output is an empty field.
4. Isosurface does not accept connection-dependent data.
5. With disjoint data fields, there may be no data crossings (i.e., points along a connection element where the interpolated data value equals the isovalue), even though the isovalue itself falls in the range of the actual data.

Components

Creates new "positions" and "connections" components. For surfaces output, the default is to create a "normals" component. Any component dependent on "positions" is interpolated and placed in the output object.

Example Visual Programs

Many example visual programs use the Isosurface module, including:

AlternateVisualizations.net
ContoursAndCaption.net
InvalidData.net
MappedIso.net
Sealevel.net
UsingIsosurface.net
SIMPLE/Isosurface.net

See Also

 Band,  Color,  Gradient,  Map,  SimplifySurface

[Data Explorer Home Page | Contact Data Explorer | Same document on Data Explorer Home Page ]