Speed CHOP

Summary

The Speed CHOP converts speed to distance, or it converts rotation rate into the number of rotation turns. ( For math-heads, it calculates the integral of a variable (channel), which is the same as calculating the area under a curve.)

If you send into the Speed CHOP a channel that has value 1, then the Speed CHOP will increase by 1 every second. If you feed it -2, it will decrease by 2 every second, and if you feed it 0, the output of Speed will not change. You can reset it to 0 by sending in a channel (whose value is greater than 0) into the second input.

This CHOP is particularly useful for calculating a point's position from its velocity (speed) or acceleration. If the input is a velocity or speed, the CHOP will output the position.

The first input contains the channels to be integrated. By default, the Speed CHOP is time-sliced, so it keeps adding to the output each frame it cooks.

The output is calculated by adding the input's channel values for every sample, starting with the sample at the Start index. Negative input values reduce the output, positive values increase it. The area is converted to the Units by dividing by samples per Unit. The cumulative values are put in the output channels.

The second input is used to reset the output to to the Reset Value. At samples where the second input is zero or less, the area is reset to zero. For example, a Wave CHOP (which is negative half the time) when passed into the second input causes the output to be zero for half a cycle.

The Speed CHOP is similar to the Area CHOP from Houdini.

Parameters - Speed Page

Order - Determines the order of the integral to use. If the input is a velocity, a First Order integral will return the position. If the input is an acceleration, a Second Order integral will return the position, and a First Order integral will return the velocity.

• First Constant - Constant to add to the entire result after integrating once.
• Second Constant - Constant to add to the entire result after integrating twice.
• Third Constant - Constant to add to the entire result after integrating three times.

Type - The type of limit function to use:

• Off - Do not limit the values.
• Clamp - Simply cut the channel value off if it is out of the Maximum/Minimum range, and replace it with the Maximum or Minimum limit value.
• Loop - Continue the channel at the other end of the interval.
• Zigzag - Mirror the values back inside the interval.

Minimum - The minimum value the output channel can have.

Maximum - The maximum value the output channel can have.

Reset - This button resets the channel(s) to the Reset Value.

Reset Condition - This menu determines how the Reset input triggers a reset of the channel(s).

• Off to On - channels are reset when the Reset input goes off to on.
• While On - channels are reset when the Reset input goes on. The channel will hold the reset value until the input turns off.
• On to Off - channels are reset when the Reset input goes on to off.
• While Off - channels are reset when the Reset input goes off. The channel will hold the reset value until the input turns on.

Reset Value - The channel(s) is set to this value when reset.

Example Uses

The Speed CHOP is a very commonly used operator. Usually it is used as a First Order integral to convert a velocity value into position.

Consider an incoming channel from a slider panel. The slider value at the minimum position is 0 and the maximum position is 1. As the slider increases in value, the ramp it generates starts increasing at a faster rate. When the slider is set back to 0, the output value plateaus and does not change until the input channel is above or below zero. In other words, a velocity of 0 means there is no change in position.

Standard Options and Local Variables

$C, $NC