Upcoming Deadlines
Fourth Homework (Tracker Video Analysis) Due Tuesday, Sept. 11
th(Next week)
15 points (10 points if late)
Fifth Homework (Analysis of Path of Action) Due Tuesday, Sept. 18
th(In two weeks) 15 points (10 points if late)
For full schedule, visit course website:
Animation123.com
Have clicker ready
Extra Credit Opportunity
Attend the premiere of RAY HARRYHAUSEN: SPECIAL EFFECTS TITAN, on Sept. 8th
at the Bal Theatre, San Leandro.
Guests of Honor for this show will be Academy Award Winning special effects artists Dennis Muren of ILM, and Phil Tippett of Tippett Studios.
Turn in proof of attendance (ticket receipt) for 10 points extra credit.
For info: http://www.bayareafilmevents.com/
RAY HARRYHAUSEN:
SPECIAL EFFECTS TITAN
Homework Assignment #4
In this assignment you’ll use tracking software to analyze the motion of a falling object.
The first step is to shoot
video reference of an object dropped from a height of
roughly four feet.
You have to be the person in
the video dropping the object
so you may need a friend to
operate the camera.
Homework #4 (cont.)
Homework #4 (cont.)
Plan your scene so that the object is clearly visible on each frame; make sure that the background is uncluttered.
Stage the scene so that the object is in frame from the moment of release until it hits the ground.
Be sure to keep the camera level and steady; the simplest way to do this is to set the camera on a table.
Shoot at least 5 takes, even if they are all more or less the same. You can record one long clip or several short clips.
Use the highest quality digital camera or camcorder that you can to minimize motion blur effects.
Tracker Video Analysis Software
For this assignment you will use Tracker, a software tool for video analysis.
To download at:
http://www.cabrillo.edu/~dbrown/tracker/
Tracker is a free program created by Doug Brown, a physicist at
Cabrillo College.
Importing Video into Tracker
Run the Tracker program on your computer and import your video clip of a falling object.
You may need to convert your clip into a format that Tracker can import (either MOV or AVI), if it's not already in that format.
Tracking an Object in Tracker
In the "Tracks" menu select "New -> Point Mass";
a Track Control window should appear.
Press the [Select Trail Length] button on the bar and select the “All Steps" option.
Go to the first frame in your clip that you want to analyze, hold down the shift key to change the cursor into cross-hairs, then click on the center of your object.
The program will mark that
position and advance one frame.
Tracking an Object (cont.)
Continue holding down the shift and marking the position of the object until it hits the ground (which should be after 15 to 20 frames).
Due to motion blur the object will "stretch" as it falls and it may be difficult to locate the exact center but just do your best to estimate the center of the blur.
Plotting the Position Data
Click on the “Choose a View”
button at the upper corner of the table and switch from Table view to Plot view.
Click on the “x” on the plot axis to bring up a menu;
change selection to
“y: Position y-component”
Tracking the Ball Drop
Horizontal Motion
Vertical Motion
Homework #4 (cont.)
In the "Edit" menu select "Copy Image -> Frame" to copy the whole window to the clipboard.
Open your favorite graphics program, such as Paint or Photoshop, paste the image, then save it to a file.
Finally, upload that image to your blog into a post called “Tracker video analysis of falling".
Visit assignment on course website to see examples.
This assignment is due by 8am on
Tuesday, September 11
th(next week).
15 points (if late, 10 points)
Assignment Checklist
* Shoot video of object dropped from a height of about four feet. Do at least 5 takes.
* Track the falling object from about the time of release until it hits the ground. You may continue tracking
bounces (optional).
* Show plots for both horizontal (x) position versus time and vertical (y) position versus time.
* Graph of vertical position versus time is roughly a parabolic arc.
* Post your screen shot and reference video in a blog entry entitled "Tracker video analysis of falling"
Survey Question
Have you looked at your classmate’s blogs?
A) Not yet
B) Looked at a couple
C) Looked at many of them
Note: You score 1 point of credit for answering survey questions, regardless of your answer.
Review Question
If the spacings near the apex aren’t quite right then the ball reverses direction at the top in an unnatural way, as if it hits an invisible ceiling.
Which of these spacings is correct?
Going up, then down
A) B) C)
“Hitting the Ceiling”
Spacing A) is correct.
Not having enough drawings near the apex looks like
hitting an invisible ceiling.
Having too many drawings
makes the ball seem to hover at the apex.
Going up, then down
Right Wrong Very Wrong
Review Question
An example of the Nyquist effect is:
A) Weightless freefall
B) Pose-to-pose animation C)Wagon wheel illusion
D)Perception of motion
E) Stretch animation
Nyquist Effect
The brain tracks the movement of the spokes by
looking for the nearest location on each frame. The Nyquist effect limits how fast a wheel can spin in an animation and still be seen as turning.
Actual Rotation Illusion
#1
#2
Wheel on frames
#1 and #2
Wagon wheel illusion is an example of the Nyquist effect.
Paths of
Action
Path of Action
The path of action is the
trajectory (tracking curve) of a moving object.
Complex Path of Action
Brick Drop Exercise
Path of Action
Brick drop exercise illustrates the path of action for falling.
http://www.youtube.com/watch?v=mPQJv1bScew
Line of Action vs. Path of Action
The path of action
indicates the trajectory for a sequence of drawings in an animation.
Individual drawings have a line of action, which
indicates the visual flow of action in that single
drawing.
Secondary Paths of Action
The path of action is usually associated with the primary motion but we can also consider paths of action for secondary motion, such as the motion of a
character’s hand, arm, foot, etc.
Primary
(Jump) Secondary
(Arm swing)
Parabolic Arcs
Paths of action of the falling brick and of a bouncing ball are
parabolic arcs
When gravity is the only force, the path of action is a parabolic arc.
Water stream
Characters in Motion
Thomas Eakins
Living beings obey the laws of physics, we’re just a little more
complex than a
bouncing ball.
Moving & Falling
Ball rolling off of a table combines horizontal and vertical motion.
Falling starts with key #4, with vertical distances increasing as 1:3:5:7:…
Horizontal distances equally spaced as with uniform motion.
Arc is the combination of uniform horizontal motion and accelerating vertical motion.
Rolling off a Table
http://www.youtube.com/watch?v=SXnwYhJrraU
Rolling off a Table, Tracked
Video tracking, frame-by-frame, shows that the horizontal motion stays uniform as the vertical motion slows out.
Uniform motion (Horizontal)
Slowing out (Vertical)
At the instant a cannon fires a cannonball horizontally
over a level range, another cannonball held at the side of the cannon is released and drops to the ground.
Which ball strikes the ground first?
Quiz Question
A) This one B) This one
C) Land at the same time
Class Demo: Fall and Fire
1
5 3
1 2
3
4 4
2
3
1 FALL
FIRE
One ball is released and falls straight down.
Other ball is fired horizontally.
At all times the balls are at the same
height.
Hit the ground at the same time.
C) Land at
the same
time
Fall and Fire by Mythbusters
http://www.youtube.com/watch?v=D9wQVIEdKh8
Mythbusters showed that a bullet dropped and
a bullet fired simultaneously hit the ground.
Falling Brick, Video Reference
http://www.youtube.com/watch?v=7ko2wYLQu2g
1 2
Falling Brick
5 3 1
3
4
5
6
The path of action for the falling brick is:
•Uniform motion in the horizontal (constant velocity).
•Accelerating motion in the vertical (slowing out as in the ball drop).
The center of the brick has a smooth and
consistent parabolic path of action
Full Parabolic Arcs
Horizontal spacings are uniform.
The rising and falling motion are the same.
Vertical spacingsslow in and out following the “Odd Rule.”
Fourth Down at Half Time
These drawings are half-way in time between the apex and the lowest points of the arc.
Those drawings are a quarter of the way down
from the apex and the lowest points of the arc.
Quiz Question
Two balls are thrown into the air at the same time;
they reach the same height but land in different places.
Which ball hits the ground first?
A) This one
B) This one
C) Land at the same time
Quiz Question
C) At the same time
All objects take the same time to fall from the same height.
Sketching a Parabolic Arc (1)
Start by picking the lower-left and lower-right points of the arc.
Draw a box, with the top line indicating the apex height.
Sketching a Parabolic Arc (2)
Divide the box into
quarters and mark the apex at the center of the upper line.
Sketching a Parabolic Arc (3)
Divide the upper boxes into quarters and mark the “Fourth Down at Half Time” points.
Sketching a Parabolic Arc (4)
Draw a smooth curve connecting the dots to create a parabolic arc.
Class Demo: Sketching an Arc
Use “4
thDown at Half Time” to
sketch the path of action for a
ball rolling off a ramp.
Common Errors in Arcs
Wrong Right
Most common error in arcs is making them straight.
This example is exaggerated to make the error obvious.
Nacho Libre
A scene in Nacho Libre has one of the worst paths of
action in cinematic history.
http://www.youtube.com/watch?v=-CCMN9UvVf8
Quiz Question
What’s wrong with the spacings in these drawings of a ball thrown in the air?
A) Vertical spacings wrong;
horizontal spacings are OK.
B) Horizontal spacings wrong;
vertical spacings are OK
C) Both vertical and horizontal spacings are wrong.
D) Actually, the spacings are OK for this path of action.
Quiz Question
C) Both vertical and
horizontal spacings are wrong.
The vertical spacings are too uniform; the motion should slow in as it rises.
The horizontal spacings should be uniform but instead they slow out going left to right.
Asymmetric Arcs
The arc is skewed; apex is closer to the left than right.
This error tends to make the long leg of the arc too straight.
Beep Beep (1952)
http://www.youtube.com/watch?v=p4YxdXw9evc
Carefully watch Wile E. Coyote’s
path of action in this scene.
Wile E. Coyote’s Path of Action
In real life, which path of action is more likely?
A) Path A B) Path B
“Beep Beep” (1952)
Wile E. Coyote travels in a parabolic arc up to the apex, then stops and falls straight downward.
Path A Path B
Bending the Laws of Physics
Wile E. Coyote takes a beating but we don’t feel that it’s animal cruelty because the laws of physics are bent,
reminding us that he’s in a cartoon universe.
Making the action more realistic would change
our emotional reaction to the scene.
“Attack of the Clones” Review
http://www.youtube.com/watch?v=9QThD0r3hZg