3.6 Visualizing 2-Dimensional Data

This section describes several ways of visualizing 2-dimensional scalar and vector data.

Colors

Using the AutoColor tool to color 2-dimensional data is the simplest visualization method available. By default, AutoColor assigns blue to the smallest values and red to the largest. (If the data are vector, the colors are based on the magnitude of the vectors).

1. Open and execute visual program .../AutoColor2D.net.

   The resulting image is a map of temperatures around the world: highest near the equator and over continents; lowest near the poles and in the oceans.

2. To display the temperature values associated with each color, connect the output tab of the ColorBar icon in the VPE window to the open input tab on the Collect icon.
3. Reexecute the visual program.

The Color tool and the Colormap Editor provide additional control of the color map:

1. Open and execute visual program .../Color2D.net.
2. Open the Colormap Editor by double clicking on the Colormap icon.
3. Select Execute on Change in the Execute pull-down menu. Any change you now make in the Colormap Editor appears immediately in the image. For example, you can experiment with:
   • moving control points (clicking on and dragging)
   • adding control points (double clicking at the desired location)
   • deleting control points (double clicking on individual points).
4. Connect the output tab of the ColorBar icon in the VPE window to the open input tab on the Collect icon.
5. Select Execute on Change in the Execute pull-down menu. The color bar from the Colormap Editor now also appears in the image. Again, a change made in the editor is immediately reflected in the image.

For more information, see AutoColor, Color, and ColorBar, in IBM Visualization Data Explorer User's Reference.

Contour Lines

Contour lines connect points of the same value in a 2-dimensional data set. The visual program in this example uses elevation data for the southeastern United States.

1. Open and execute visual program .../Isosurface2D.net.

   The contour line that appears in the image has an isosurface value of 0 meters (sea level).

2. Open the Isosurface configuration dialog box.
3. In the value parameter field, change "0.0" to "20" and click on OK. The dialog box closes.
4. Select Execute on Change in the Execute pull-down menu and note the change in the contour line.
5. Reopen the Isosurface configuration dialog box and type "0 20" in the value parameter field.
6. Click on OK. The image now consists of two contour lines.

For more information, see Isosurface in IBM Visualization Data Explorer User's Reference.

Streamlines

If your 2-dimensional data set consists of vectors, you can create streamlines that trace the path of a massless particle in a vector field.

1. Open and execute visual program .../Streamlines2D.net. The image is a set of streamlines that follow a wind field over the surface of the earth.
2. Change the number of streamlines by changing the value of the density parameter in the configuration dialog box of the Sample tool.
3. Reexecute the visual program.

Note: Streamlines can be generated in other ways as well. For example:

1. Pass a list of 2-dimensional positions to the start parameter in the Streamline configuration dialog box by either:
   1. inserting a VectorList interactor stand-in (from Interactor in the categories palette) into the visual program, and connecting it to the start parameter tab of Streamline or
   2. typing the start positions in the configuration dialog box for Streamline.

2. Use the Grid tool (from Realization in the categories palette) to create a particular set of start positions. Any field that contains positions can be used as the starting point for streamlines.

   This sample visual program contains a Grid tool. Connect it to the start parameter tab of Streamline. It generates a 3 × 3 grid of points. Modify it to create a 10 × 3 grid of starting points.

3. Use the Probe tool (from Special in the categories palette) to select starting points in the Image window.

   This sample visual program contains a Probe tool. (Compute is used to make the value of the probe point 2-dimensional.) Connect the output of Compute to the start input tab of Streamline, and then move the probe (i.e., enter cursor mode, using the View Control dialog box).

See Grid, Probe, and Streamline in IBM Visualization Data Explorer User's Reference.

RubberSheet

You can "warp" the representation of 2-dimensional data with the RubberSheet tool.

1. Open and execute visual program .../RubberSheet.net. The image represents elevation above sea level in the southeastern United States. Regions of greatest elevation are colored red; regions of lowest elevation, blue.
2. Open the RubberSheet configuration dialog box.
3. Change the value in the scale parameter field to ".002."
4. Click on OK and reexecute the visual program. The contrast of variation is greatly increased.

For more information, see RubberSheet in IBM Visualization Data Explorer User's Reference.

You can also add contour lines to a Rubbersheet image:

1. Select Realization in the categories palette and then Isosurface in the tools palette.
2. Place the icon to the right of RubberSheet.
3. Connect the output of RubberSheet to the first input tab of Isosurface (the only connection that Data Explorer will allow you to make). Make sure that you do not break the connection to Shade.
4. Open the Isosurface configuration dialog box.
5. Change the number parameter value to "10" and click on OK.
6. Select Structuring in the categories palette and Collect in the tools palette.
7. Place the Collect icon below Isosurface.
8. Connect the outputs of both Shade and Isosurface to the inputs of Collect (again, Data Explorer will allow only valid connections).
9. Disconnect Image from Shade.
10. Connect the output of Collect to the input of Image.
11. Reexecute the visual program. The result is a set of colored contour lines combined with the Rubbersheet image.

You can change the color of the contour lines:

1. Select Transformation in the categories palette and then Color in the tools palette.
2. Place the Color icon to the right of RubberSheet and Collect.
3. Open the Color configuration dialog box.
4. Delete "(no color added)" in the color parameter field and type in "black" (the quotation marks are unnecessary and will be added by Data Explorer).
5. Click on OK.
6. Move the output of Isosurface from Collect to Color.
7. Connect the output of Color to the input of Collect.
8. Reexecute the visual program.

See Color and Isosurface in IBM Visualization Data Explorer User's Reference.

2-D Scalar Glyphs

In this example, elevation data are represented both by color and by glyphs (the black circles).

1. Open and execute visual program .../AutoGlyph2DScalar.net. The elevation values range from higher (orange; larger circles) to lower (blue; smaller circles). The size of each glyph (circle) is proportional to the data value it represents. To display these values:
2. Open the configuration dialog box for AutoGlyph.
3. In the type parameter field, replace "(input dependent)" with "text" and click on OK.
4. Reexecute the program. The actual data values that appear are called text glyphs.

See AutoGlyph in IBM Visualization Data Explorer User's Reference.

2-D Vector Glyphs

Glyphs can be used to represent vector as well as scalar data.

• Open and execute visual program .../AutoGlyph2DVector.net.

  Again, data values are represented by color and by glyphs (arrows). In this example of wind velocity data, colors represent the magnitude and arrows the direction. (The black squares signify missing data or data omitted as invalid by the Include module in the program.)

See AutoGlyph in IBM Visualization Data Explorer User's Reference.