Map

Category

Transformation

Function

Applies a map to a field or value list.

Syntax

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

Inputs

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.

Outputs

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.

input	is the field or value list to which map is applied.
map	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.)
source	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.
destination	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").

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
"data"	"colors"	color mapping
"positions"	"data"	data mapping
"data"	"data"	arbitrary tabular function

Notes:

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.

Components

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

AlternateVisualizations.net
Interop.net

ManipulateGroups.net

MappedIso.net
PlotTwoLines.net
Thunder_cellcentered.net
UsingMap.net
SIMPLE/Map.net

See Also

 AutoColor,  Color,  MapToPlane