SRTFormula

The Path->SRTFormula command in the Motion module is a custom effect for animating objects. With SRTFormula, you may type in equations to control the transformations of one model as a function of the transformation of another model.

The equations may use standard mathematical functions and symbols such as +, -, *, SIN, COS, PI, TAN, SQRT, RAND, and TIME. In addition, the equations may incorporate the transformation of the icon for the effect, providing an easy and intuitive way to animate parameters in the formulas.

With this tool, you can easily obtain precise motions of models that would be otherwise tedious or impossible to generate.

Procedure

1. Create two models: the source and the target objects (the source and target may be the same model). These objects may or may not be animated.
2. Choose the Path->SRTFormula command.
   
   The SRTFormula dialogue box is displayed:
   
   
3. Set the parameters as desired.
4. Follow the prompts to select the source object and the target object.

Parameters

Reserved Variables

These are available to you as variables for equations. The variables SX, SY, SZ, RX, RY, RZ, TX, TY, and TZ correspond to the scale, rotation, and translation values of the models. To the left of an equation, they represent values for the target's transformation, while to the right of an equation, they represent values for the source's transformation. For example, an equation such as TX = TY + TZ sets the X translation on the target model to the sum of the Y and Z translation on the source model.

The variables A, B, C, and D in the animated Formula effects can be keyframed using Effects->Edit Parameters in the Motion module

Although not explicitly listed, the SRTFormula Icon transformation variables ISX, ISY, ISZ, IRX, IRY, IRZ, ITX, ITY, and ITZ are available to be used in the equations.

For more general information on writing equations in SOFTIMAGE custom effects, see SOFTIMAGE Custom Effects Formula.

User Variables

Any letters or words may be assigned by you for these variables.

Equations 0 to 9

You may fill any number of equations, but each equation must be less than 40 characters. See SOFTIMAGE Custom Effects Formula for details on writing equations.

Program Variables

Can be keyframed and used in equations.

Copy Xfms by Default

With this option selected, transformation elements that aren't explicitly set by equations are copied from the source object.

Random Number Seed

A value with which to seed the random number generator RAND.

Start and End frame

The frame numbers between which the effect is active.

Frames Per Second

For the motion timing to be correct, this option must be set to the same frame rate being used in SOFTIMAGE 3D, usually 30.0 or 24.0 frames per second.

Next, Previous, Delete, Key, and Frame

For the animated effects, Next advances to the next keyframe, Previous goes back to the previous keyframe, Delete removes a keyframe, and Key sets a keyframe at the frame you specify in the Frame text box. These controls are available only after you have set the initial parameters in the dialogue box and clicked Ok. To return to the dialogue box and edit keyframes for the effect, select the effect icon and choose the Effects->Edit Parameters command in the Motion module.

Last updated 02-apr-1998