IBM Visualization Data Explorer User's Reference

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Applies a map to a field or value list.


output = Map(input, map, source, destination);

Name Type Default Description
input field, value, or value list none field to be mapped
map scalar, vector, or field identity map to be used
source string "positions" component used as index into map
destination string "data" component in which to place the interpolated data.

Name Type Description
output field, value, or value list mapped input field

Functional Details

Map is a general purpose module which maps from one field to another.


is the field or value list to which map is applied.


is the map to be applied to the input object. Unless this parameter specifies a single value, it should contain both a "positions" and a "data" component.

Because the module performs interpolation, the map it applies to the input must also contain either (1) a "connections" component or (2) "faces," "loops," and "edges" (see "Faces, Loops, and Edges Components" in IBM Visualization Data Explorer User's Guide). The "data" component may be dependent on "positions," "connections," or "faces." (If the field contains faces, loops, and edges, the data must be dependent on faces.)


specifies the component of input that is to be used for indexing into the "positions" component of map. The value of the corresponding "data" in map is determined by interpolation between the "positions" in map, using the interpolation elements of map (either "connections" or "faces", "loops", and "edges"). source is ignored if input is a value list.


specifies the output component in which interpolated values should be placed. If input is a value list, then the interpolated values simply replace the values in input.

The Map module steps through the source component of input. For each item in that component, the module looks up that value in the "positions" component of map and finds the corresponding value in the "data" component of map, interpolating if necessary. The resulting value is placed in the destination component of output (see Figure 3).

Figure 3. Mapping from one field to another. This figure shows an input field and a map field, both with two-dimensional positions and triangle connections. The figure shows how a data value is found for the position (a,b) in the input field by interpolating in the map field when the parameters to the Map module are input= Input Field, map= Map Field, and source and destination default to "positions" and "data" respectively.

As with all maps in Data Explorer, the map field must have "positions", "data", and "connections". Since the source component is "positions", the "positions" component of input is used to index into the "positions" component of map. Thus we lookup the position (a,b) in the map field. This leads us to the triangle connecting positions 0, 1, and 2 in the map field. The data values corresponding to positions 0, 1, and 2 are interpolated to yield the result 1.3, which is then placed in the "data" component of the output of Map (since destination is "data").

Figure map not displayed.

So, for example, if source is "positions," destination is "data," input is an isosurface, and map is a 3-D field with temperature values, then Map steps through the "positions" component of the isosurface and finds the temperature value for each position, interpolating if necessary. The resulting temperature value is placed in the "data" component of the output field.

If map is a value, the Map module adds to output a destination component that (1) contains one element for each element of the source component and (2) derives its dependency from the source component. All elements in this component have the value given them by map.

The following table summarizes some of the uses of Map.
Source Destination Use
color mapping
data mapping
arbitrary tabular function


  1. The dimensionality of the positions in input and in map must agree and must also match the dimensionality of the connections in map. That is, if map has 2-D connections (quads or triangles), the positions must also be 2-D.
  2. There are few constraints on Map' functionality. For instance, the Color module is generally preferable for performing mapping, because that module prevents the formation of invalid colors, whereas Map does not.


If input is a field, a new component name, specified by destination, is created. All other input components are propagated to the output.

If input is an array, the output is an array.

If any source values cannot be interpolated, an "invalid positions" or "invalid connections" component (depending on the dependency of the source parameter) will be created, and values that are not interpolated will be marked invalid.

Example Visual Programs

See Also

 AutoColor,  Color,  MapToPlane

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