SciVisFall2008/Assignment 2

This is your third assignment for CS 5630/6630.

The assignment is due at midnight on October ??, 2008. You will need to use the CADE handin functionality to turn in your assignment. The class account is "cs5630".

This assignment was successfully tested in release 1.2.1rev1336. It should work fine in releases >=1.2.1rev1336. Check your release before starting your work and upgrade it if necessary.

The purpose of this assignment is to make sure you understand (and experiment with) the basic concepts involved in the visualization of 2D scalar and vector fields.

Examples of visualizations of 2D scalar and vector fields were provided in the lectures and can be found here and here.

As you work on the assignment, we encourage you to read the available documentation on both python and VTK. Remember that VisTrails allows you to easily access the VTK documentation. To see the documentation of a VTK module in the Modules panel, just right click on its name and choose View Documentation in the context menu. Analogously, you can right click on a method's name in the Methods panel to see it's documentation. Some of the problems will require you to use VTK modules you might not have previously seen. These are indicated in the problems.

General Hints

Some of the fields in this assignment are such that most of the points in the field have values in a small region of the range. Because of this, a linear path through the color space might be inappropriate. You might consider using vtkColorTransferFunction for more effective results.

When generating visualizations that overlay multiple actors, it will be convenient to displace some of them along the Z direction so they "stack" the right way. Use the "AddPosition" method on the vtkActor module to do that.

Data

The data for the four problems of this assignment are in four files: grand_canyon.vtk and grand_canyon_small.vtk (problems 1 and 2), vector_field_2008.vtk and vector_field_norm_2008.vtk (problems 3 and 4).

• grand_canyon.vtk is DEM of the Grand Canyon National Park.
• grand_canyon_small.vtk is a downsampled version of the above file.
• vector_field_2008.vtk is a 2D vector field
• vector_field_norm_2008.vtk is the normalized version of the above 2D vector field

The four files are packed into a single zip file called Hw2data.zip. The task of unzipping and locating these files is already done in the starting vistrails file for this assignment: Assignment2.vt. You should solve the problems by working directly in this vistrails file.

Exercise 1: Basic scalar field techniques

You will design colormaps for a dataset. In particular, you will design two different colormaps for two different tasks. The dataset you are given is a digital elevation map (DEM) of the Grand Canyon National Park. To give you context for this problem, we include here a google map of the area:

<googlemap version="0.9" lat="36.503013" lon="-112.519226" type="terrain" zoom="9" width="400" height="450"> </googlemap>

The elevations are given in meters, and the range of the data is [548.0, 2835.0].

Hint: as the original dataset is large, you should test your visualizations using the 
downsampled version (grand_canyon_small.vtk). It will work better on slower machines.

(a) Apply the colormap design principles described in class to create a visualization where it is easy to tell which of two points are higher. Tag the final version of this visualization as Problem 1a and describe in the notes why you chose this colormap.

(b) Apply the colormap design principles described in class to create a visualization where it is easy to tell the height of any given point. Tag the final version of this visualization as Problem 1b and describe in the notes why you chose this colormap.

(c) Generate a visualization that is suited to both previous tasks. Tag the final version of this visualization as Problem 1c and describe in the notes why you chose this colormap.

Grads only

(d) Generate colormaps that give a good visualization of the plateau (the green area in the google map in terrain view) on the east part of the DEM. Tag the final version of this visualization as Problem 1d and describe the technique used on the notes. Potentially relevant modules for this task: vtkColorTransferFunction.