An introduction to stereographic projection
Welcome to this demonstration of java courseware from Resource Dynamics.
Two applets are ready for this pre-release demostration:
- A 3D model to convey the concept of stereographic projection
- "Mini cauldron" A stereo plotting applet that lets you solve many
common stereographic problems at the click of a mouse.
The 3d model
This applet demonstrates a simple 3d projection system that enables the
user to tilt and rotate using the sliders beside and below the applet.
The user can enter the dip direction and dip angle in boxes. The program
then creates a wireline box diagram of such a plane. It draws the plane
placed within a hemisphere and it draws this plane transfered onto a
plot circle. A small yellow 'balloon' indicates the top pole of the
sphere and is intended to indicate the "light source" for the equal
angle projection. The only "cheat" is that the plot circle is dropped
some distance below the hemisphere so that it can be better viewed without
the hemisphere obstructing the view.
Mini Cauldron Stereo-plotter applet
Mini cauldron pops up in its own frame. This means it can be resized
and dragged outside the browsers window and used for a variety of problems.
Java security means that the window will have a warning message. Java
is inconsistent about closing windows. If you run this applet through
the java applet viewer then close it by using the normal buttons. If
viewed from Netscape you should use the hide option in the file menu.
To enter dip data the user types mumbers into the appropriate box and then
clicks the appropriate button. If the data is valid the screen will redraw.
Intended student interactions
The student is intended to experiment entering planes and then viewing them
on the block model from various angles and directions (using the slider bars).
The go on to seeing what this plane would look like if placed inside a
hemisphere, and then projected onto a plane.
Mini cauldron functions
- Mouse clicking. Clicking the mouse in the circle will cause the dip amount
and direction to appear in the first 2 boxes. The third box will show the
angle to the last click (less than 90 degrees).
- Data: add plane. This will add a great circle based on the data in the
first
two data boxes. The data can be entered directly or result from a mouse
click.
- Data: add point. This adds a point (cross) based on the data in the
first 2 data boxes.
- Data: add cone: adds a small circle based around the point given in the
first 2 boxes. The radius is given in the third box. Two mouse clicks followed
by this option creates a circle centred on the second click passing through the
first.
- Data: delete last: Mini-Cauldron stores data in the order in which it
is entered. This option removes the last item in the sequence.
- File: clear: Removes all data from the store.
- File: Hide: makes plot window disappear (use with browsers)
- File: About: shows information about the mini cauldron program.
You may choose to run this applet using the (free) java appletviewer rather
than a browser.
Click to launch!
Intended Student interactions
This program can solve a wide variety of stereographic problems. The program
can be resized or maximised and run after the browser is closed. Some of sample
of possible exercises include:
- Finding the intersection between 2 planes (enter the planes numerically
and then click on the point of intersection).
- Find the angle between two planes (enter the poles of the planes and then
click on both of them).
- find the sigma directions from a pair of complementary faults.
- Slope stability analysis
Nigel Stuart PhD
106 Metcalf Avenue
Red Deer
Alberta
Canada
T4R 1N8
nstuart@agt.net www.agt.net/public/nstuart/rd.htm