Wednesday, May 13, 2009

Teaching in 3D

One of the things that I loved about being a Tech Ed teacher was the freedom to combine science & math concepts with real world applications & a bit of summer camp crafts. Wehn I first came to work at NC State I was on a grant that looked at how students interpret visualizations. One of the outcomes of this work was that I learned a good deal about 3D & how 3D works. I even got a chance to build and program a two projector, linear polarized, rear projection immersion screen (that is in an attic somewhere on campus). But what really stuck with me was how true 3D images were created & how we trick our brain's into seeing them. Now, add to this the opportunities I encounter to do 1-hour sessions with visiting high school or middle school students & I am a one-woman 3D show.

Recently I had the opportunity to work with students through the Satellitte program on campus, on which I would like to speak more on later, but I really want to discuss how 3D works & how easy it is to use it to teach certain principles.

I like to start with a conversation about what 3D is and how we add to the X/Y coordinate plane with Z. Then I discuss One-eyed pirates and why they walk into tables (seriously, you have to be funny). We discuss how depth perception works and how your brain combines the images of your left and right eyes to make a composite. My favorite trick is to have students raise their index finger and alternate closing eyse. "Did your finger move? Did you move your finger?" This starts a dialogue on dominant eyes, etc.

The premise of 3D is that you are sending separate images to each eye. Now the question is - How do you do that?

There are various types of 3D. I find that if you follow the historic time line of 3D progression it is easier for students to understand.

Stereo Pairs

Stereo Pairs are the easiest for students to understand. They have all experienced the ViewMaster of old. The one with the wheels of images. I pass out a few of the slide wheels and ask them to count the number of images.


They will find that there are duplicates of each picture. A stereo pair of each scene. One for each eye. Stereo pairs are slightly off from one another. They are not the same image, but two separate images taken roughly 2 inches apart. Here comes the "Aha" moment. Why 2 inches? Because your eyes are roughly 2 inches apart.

Now how long have stereo pairs been around? The idea was first captured by Charles Wheatstone, but it took Sir David Brewster to actually create the first Stereo Pair Viewing device and exhibited it at the world's fair in 1851. Of which Queen Victoria was a huge fan.

So how do you take Stereo Pairs? Why you take a picture two inches apart. The most effective way of doing this is to have a 3D camera that takes 2 pictures at the same time. Personally I am a fan of using two cameras mounted next to each other and you mechanize the shutters together. Or you could do the good ol' astronaut shuffle. The rumor is that they couldn't afford the weight of the 3D camera so the astronaut's took one picture and then movedr oughly two inches to the right and took another :)

So all 3D effects come down to Stereo Pairs. But how do you get everyone in an audience to see the same image at once, like in a movie? This is where glasses come in. And the first 3D glasses are the icon of the 1950s - Red/Blue

Anaglyph or Red/Blue
http://en.wikipedia.org/wiki/Anaglyph_image
I like to use the concept of computer monitors & RGB. All LCD displays are made up of the colors RGB, and thus all images on these displays are a combination of these colors. So to make a Composite 3D image you need to get your eyes to see different images, the Anaglyph method uses color. In one image you take all the Red out of an image (I use Photoshop) so that only the Green & Blue are left (more like Cyan) and in the other you take all the Green & Blue out of the image so only Red is left. It is important that the left image be the Red one and the right image be the Green/Blue one, otherwise you will have to put your glasses on backwards.

I found the USGS site (which hosts a good deal of Anaglyph pictures) to be an invaluable source of creating these 3D images.

Glasses
Now you can buy glasses at http://www.3dglassesonline.com/ (where I buy mine). Or you can make your own - my personal preference. There are two ways to make glasses. Start with already made frames or create your own frames. I have done it both ways. The cheapest cardboard frames I could find were from Oriental Trading Company. The biggest issue with them is that the eye holes are a bit small, but they are fun & funky shapes. If you make your own glasses, you either need to use 11x17 paper to get the side ear pieces or you create masks and use rubberbands or string to tie around their head. If you have time, letting your students decorate their masks can be a fun art activity.

Once you have your glasses, now you need to add your colors. I use the transparent wrapping paper in shades of red & blue. It is hard to get the right blue & I find I have to double up. I pre-cut squares for my students, so they only have to tape it on. The reason making the glasses is so integral is it makes them think about which eye needs to be red and which needs to be blue. Then we can discuss how colors filter. I like to have an example Anaglyph image before I composite it displaying on the screen so that they can see which images disappear or are blacked out by which eye.

Thanks to a commenter ( luchianken)- I realized the picture I pulled from http://www.3dglassesonline.com/how-do-3d-glasses-work/ is completely wrong! I'll look for a new illustration

I then like to show them a few websites that they can use to view 3D photographs.
http://3dparks.wr.usgs.gov/
http://dogfeathers.com/java/hyprcube.html

(On a side note, I don't let students look for 3D pictures - their are some NSFS images out there)

Then you can start talking about how the latest 3D works with light polarization instead of color and your students will have something to explain to their parents next time they are in line at IMAX :)

4 comments:

Beth said...

For some super cool 3D movies and images online check out the STEREO project. 2 satellites orbiting the sun! Teachers can get a set of glasses for free if they email the program. My favorite is when they catch a solar flare coming straight at you! http://www.nasa.gov/mission_pages/stereo/main/index.html

Caryn said...

So cool.. you break it down so nicely!

luchianken said...

your drawing is totaly wrong! Cyan filter will never let red light pass thrrough, it will absorb it. It is the same with red filter. It will absorb cyan radiation and only let red light pass!

Bethany Smith said...

Thanks for letting me know the illustration was incorrect. I have taken it down.