Animation

Animation

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Geometry Expressions allows you to set a range of values to a variable, then run through the range to animate your drawing, using the familiar video playback interface. To animate a drawing:

  1. Select a variable to drive the animation.
  2. Assign a range of values to that variable.
  3. Press Play button (Play button ).

In the figure below we select θ to crank the linkage:

Animation 

From other interactive geometry applications, you may be familiar with animating points along line segments or curves. Geometry Expressions provides this animation capability as well, using the constraint point proportional along a curve.

A point proportion t along a curve is defined thus:

for:                        definition:

line segment AB         point (1-t) A + tB

circle                         point on the circle that subtends angle t at the                                         center

locus or envelope         point at variable value t

For example, in the following drawing, D is defined proportion t along AB, and E is defined proportion t along BC. The curve is the locus of F as t varies between 0 and 1:

 

To animate this, we assign t the range 0 to 1, then push Play.

The construction of both locus and envelope curves can be defined in terms of any variable. For example, starting with the drawing below:

 

…we create a locus over values of t, keeping other variables constant: