To do these exercises you must run DX and the vector field program. When the image window appears, click on the Windows menu of the Image window and select the Open VIsual Program Editor (VPE) item. The program source should appear.

Remember that you can get help in DX on any module by selecting the "context sensitive help" item from the help menu, then clicking the left mouse button on a module.

• Make the streamline diameter proportional to the vector magnitude.
  
  1. Disconnect the Tube and the Color module below it.
  2. Add a Compute module by:
     1. Clicking on the Transformation Catagory at the upper-left side of the VPE.
     2. Clicking on the Compute item of the list in the lower-left side of the VPE.
     3. Clicking below the Tube module to place the new Compute module.
  3. Add a RubberSheet module by:
     1. Clicking on the Realization Catagory at the upper-left side of the VPE.
     2. Clicking on the RubberSheet item of the list in the lower-left side of the VPE.
     3. Clicking below the Compute module to place the new Rubbersheet module.
  4. Add a Normals module by:
     1. Clicking on the Rendering Catagory at the upper-left side of the VPE.
     2. Clicking on the Normals item of the list in the lower-left side of the VPE.
     3. Clicking below the RubberSheet module to place the new Normals module.
     4. The Normals module is necessary because the RubberSheet module does not calculate lighting information.
  5. Connect the output of the Tube module to the Compute module.
  6. Connect the output of the Compute module to the RubberSheet module.
  7. Connect the output of the RubberSheet module to the Normals module.
  8. Connect the output of the Normals module to the Color module.
  9. Double-click the Compute module and enter the string mag(a) in the "expression" field.
  10. Execute the program by selecting the Execute Once item from the Execute menu.

  The program should now look like this, (with the Compute dialog box open) and will generate an image with variable diameter streamlines.

• Grow the streamline as a time sequence.
  
  1. Add a Compute module by:
     1. Clicking on the Transformation Catagory at the upper-left side of the VPE.
     2. Clicking on the Compute item of the list in the lower-left side of the VPE.
     3. Clicking above the StreamLine module to place the new Compute module.
  2. Add a Sequencer module by:
     1. Clicking on the Special Catagory at the upper-left side of the VPE.
     2. Clicking on the Sequencer item of the list in the lower-left side of the VPE.
     3. Clicking above the Compute module you just added to place the new Sequencer module.
     4. Double-click the Sequencer module to show the sequencer widget.
  3. Connect the output of the Sequencer module to the Compute module.
  4. Connect the output of the Compute module to the fourth input ("head") of the Streamline module.
  5. Double-click the Compute module and enter the string a*5 in the "expression" field. This factor of five scales the time so that the streamlines move at a reasonable rate.
  6. Execute the program by clicking the play icon on the sequencer widget.

  The program should now look like this, and will generate one time step image in which different streamlines have different lengths depending on the local field strength (treating the field as a "velocity"). An mpeg animation shows about 43 frames.

• Color vector glyphs by their magnitude
  
  1. Disconnect the Autoglyph and the color module below it.
  2. Add a Compute module by:
     1. Clicking on the Transformation Catagory at the upper-left side of the VPE.
     2. Clicking on the Compute item of the list in the lower-left side of the VPE.
     3. Clicking below the Autoglyph module to place the new Compute module.
  3. Add a ColorMap module by:
     1. Clicking on the Special Catagory at the upper-left side of the VPE.
     2. Clicking on the ColorMap item of the list in the lower-left side of the VPE.
     3. Clicking below the Compute module you just added to place the new Colormap module.
  4. Connect the output of the Autoglyph module to the Compute module.
  5. Connect the output of the Compute module to the first input of the ColorMap module and to the first input of the Color module.
  6. Connect the output of the ColorMap module to the second input of the Color module.
  7. Double-click the Compute module and enter the string log(mag(a)) in the "expression" field. This expression log-compresses the large data range so that the a color range is easier to see.
  8. Execute the program by clicking the play icon on the sequencer widget.

  The program should now look like this, and will generate an image in which the vector glyphs have a color range.

• 2D slice of the 3D field.
  We will slice the 3D field to show 2D methods, but you could clearly use the same techniques for fields which were originally 2D. The presentation of methods will be somewhat compressed.
  1. Add the following modules (refer to the program for module placement):
     1. A Slice module from the Import/Export catagory.
     2. A Reduce module from the Import/Export catagory. Set the factor to 2.
     3. A Autocolor module from the Transformation catagory.
     4. An Autoglyph module from the Annotation catagory.
     5. A Color module from the Transformation catagory. Set the "color" field in the module dialog box to "black".
     6. A Collect module from the Structuring catagory.
     7. A Image module from the Rendering catagory.
  2. Connect the modules as shown in the link above. The wire coming in the top of the program fragment is from the import module.
  3. Execute the program by selecting the Execute Once item from the Execute menu. A new image window will appear with a 2D slice in it.

  The program should now look like this, and will generate an image in which the vector glyphs are black and the background is colored by the vector magnitude.