Vector Field
Exercise

Description

In this exercise you will build a 3D volume filled with vectors (arrows). Each vector will point in a different direction and have a different color.

In visualization, vector fields are often used to indicate the flow of a fluid through a volume. Each arrow indicates the direction and magnitude of the flow at a point in the volume. To show changes in the fluid flow, the vector field is animated, causing the vectors to change direction, length, and color.

This exercise focuses upon use of IndexedFaceSet and Coordinate nodes and the PROTO syntax.

VRML Concepts

This exercise requires you to understand and make use of the following VRML features and concepts:
• Basics
  • VRML file structure
  • Comments
  • DEF and USE
  • VRML Data types
  • PROTO
  • EXTERNPROTO
• Shapes and appearance
  • Shape node
  • Appearance node
  • Material node
  • IndexedFaceSet geometry node
  • Coordinate node
• Grouping
  • Transform node

Files

Here are the files you may use to get started with this exercise:
• vecfld1.wrl
  This is a VRML world that uses the vector you will create.

Tasks

1. Create and edit a new VRML file named "vector1.wrl".

   In "vector1.wrl", build a flat arrow-shape using an IndexedFaceSet geometry node. Make the arrow conform to the following specifications:

   • Build the arrow in the X/Y plane.

   • Build the arrow pointing in the direction of the positive Y axis.

   • Construct the arrow with the following dimensions:

     Parameter	Dimension
     total vector height	1.0
     body width	0.2
     body height	0.75
     tip width	0.5
     tip height	0.25
     origin	center base of arrow body

     HINT: Sketch your arrow on a piece of paper first. Then write the 3D coordinates for each corner, and number each corner. This will give you the data you need to type in as coordinates and coordinate indexes for the IndexedFaceSet node.

     HINT: Build the tip with one triangle and the base with one rectangle.

     HINT: Remember, use a "-1" index value to delimit faces.

   • Make the material appearance of your arrow shape as follows:

     Field	Value
     ambientIntensity	0.0
     diffuseColor	0.8 0.8 0.8
     emissiveColor	0.0 0.0 0.0

   • Enable the faces to be viewed from both sides.
     HINT: Add the solid field with a FALSE value.

   SOLUTION: vector1.wrl

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2. Copy your "vector1.wrl" file to "vector2.wrl" and edit it.

3. Your task is to duplicate the arrow you just created. The original and the duplicate should be placed into the same VRML file. The duplicate should be rotated around the Y axis by 90 degrees. The pair of arrows will intersect down the middle of the arrow.
   HINT: You can use DEF and USE.

   SOLUTION: vector2.wrl

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4. Copy your "vector2.wrl" file to "vector3.wrl" and edit it.

   To build a vector field you're going to need dozens of arrows, all with approximately the same shape. Wouldn't it be nice if there was a Vector node? Your task is to modify the "vector3.wrl" file to create a Vector node. Add a PROTO wrapper around the vector shape. Make sure that it conforms to the following specifications:

   • The PROTO name should be Vector (with a capitol "V")

   • Your Vector prototype should contain four fields with the following definitions:

     Data Type	Field Name	Default Value
     SFVec3f	translation	0.0 0.0 0.0
     SFVec3f	scale	1.0 1.0 1.0
     SFRotation	rotation	0.0 1.0 0.0 0.0
     SFColor	color	0.8 0.8 0.8

     HINT: Connect the translation, rotation, scale, and color fields of the PROTO interface to your vector shape using the IS syntax.

   You can test your new Vector node by temporarily adding a line to the end of your file, like this:

   Vector { }

   Try adding translation, scale, rotation, and color fields and values to your Vector node test.

   SOLUTION: vector3.wrl

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5. Copy your "vector3.wrl" file to "vector.wrl" and edit it. Remove your test node (if any) from the bottom the file after your Vector PROTO.

   Load "vecfld1.wrl". This file contains an EXTERNPROTO that looks in your "vector.wrl" file and loads your Vector node PROTO. The vector field file then uses your node to create a 3D block of arrows, all pointing in different directions.

   SOLUTION: vecfld1.wrl