IceBreaker:
Visualization of Antarctic
Ice Streams
Khairi Reda mreda2 at uic dot edu |
Dennis Chau koracas at gmail dot com |
Video
Download
Introduction
The study of the movement of ice sheets in Antarctica and Greenland has become important in the last few months as changes to these ice sheets are occurring at a much faster rate than previously thought. While there are many tools that can be used for the visualization of vector fields that represent flows, these tools often produce a static snapshot of the entire dataset, or rely extensively on animation. These techniques work well when studying flows limited around some well defined boundary (example: aircraft wing). It is not clear if these techniques scale well for continent-scale flow fields.
The goal of this project is to implement a visualization tool that can be used to study the patterns of ice flow in Antarctica and Greenland. The tools will combine some of the established techniques in flow visualization along with modern visual analytic and interaction schemes. This will allow scientists to look at different representations of the same ice velocity data, as well as compare different flow models (or observational data) of the same geographic area.
Visualization
In order to offer a useful tool to analyze ice flow, multiple windowing options are offered in the visualization.
The controls and conveniences offered by each mode will be explained in detail further on.
Meanwhile, the possible windowing combinaitons are as follows:
The visualization starts with the Dataset Choice Box.
From here a user can select a dataset by:
The Single Visualization Window allows the user to see one data set at the resolution of the monitor. Accordingly, the Double Visualization Window allows the user to see two data set at half the resolution of the monitor. This allows the user to view different datasets, such as Antarctica and Greenland, concurrently. In doing so a user can compare these two areas. Each visualization window was designed to be an independent entity, as such the control scheme for a Single Visualization Window applies to a Double Visualization Window.
One function of this component allows the user to specified vizualization mode form the following choices:
General Controls
These controls apply to all modes of visualization.
This component allows users to interpret the color scale.
In Particle Mode the color scale reprsents velocity.
In Arrow & Contour Mode the color scale reprsents time.
After the datasets have been selected, a transparency controler will appear.
This allows the user to control the opacity of both the Geographic Map and Velocity Map.
The velocity map gives the user an overall view of the underlying velocity grid.
This allows them to easily choose potential areas of interest.
Sync'd Double Visualization Windowing allows the user to syncronize the left visualization window with the right visualization window. This syncronization mirrors mousewheel and dragging between the two windows. This is convient because it allows users to investigate in two different modes over the same area. Or it allows users to compare a simualted data set on flow compared to an emperically collected data set.
Datasets
There are three datasets that go into the visualization program:
Algorithms
Particle simulation:
The algorithm for the particles is very similar to the algorithm used in RainTable: the generators produce a number of particles at a specified rate (controller by slider). The particles are assigned an initial random position close to the generator. Each particle is simulated once every simulation iteration. The algorithm moves the particle N step (which could be exaggerated by the "time scale" slider) at every iteration. Increasing N increases the speed of the particles. However, unlike RainTable, an increase of N does not distort the actual flow model. This is because the program does N lookups on the velocity vector field as opposed to exaggerating the speed of the particle. However, the time scale slider can potentially distort the flow. Therefore, it's set to a moderate value (10 by default).
Streamlines:
The streamline algorithms takes a curve drawn by the user, chops the curve into a number of points (determined by the "density" slider). We refer to these points as "source points". The program calculates streamlines that start from the sources points, and renders them on the screen. The algorithm used to calculate the streamline is idential to the one used to determine the movement of particles. The streamlines are calculated in the CPU, and later uploaded to the GPU as vertex arrays so that they can be subsequently rendered at interactive speeds.
Multi-level-of-detail image viewer:
The image viewer used to load the satellite texture works by determining the optimal detail level (given the current zoom on the dataset), determines the viewable sections of the dataset, and loads the appropriate tile.
Acknowledgement
We would like to thank Eric Rignot of the Jet Propulsion Laboratory for providing ice velocity datasets, and Paul Morin of the Antarctic Geospacial Information Center for providing Antarctica maps and satellite images.
Last update: dec 11, 09