PositionSpeed

Calculates the position speed from X and Y coordinate variables and creates a new continuous variable.

Syntax

PositionSpeed(varX, varY, deltaT, smoothRadius)

Parameter	Type	Description
varX	variableReference	Reference to the variable.
varY	variableReference	Reference to the variable.
deltaT	number	Time step for speed calculation
smoothRadius	number	Smooth parameter. See Comments.

Reference to the new variable

Note

PositionSpeed operation calculates the scalar speed of a pair of the position variables.

First, for each data point of a Position variable PosX[T], where T is time, the raw scalar speed is calculated:

dX = PosX[ T + DeltaT ] - PosX[ T ]
dY = PosY[ T + DeltaT ] - PosY[ T ]
RawScalarSpeed[ T ] = sqrt( dX*dX + dY*dY ) / DeltaT

If there is no data point at time T+DeltaT, a linear interpolation is used to calculate PosX[T + DeltaT] and PosY[T + DeltaT].

Second, RawScalarSpeed is smoothed with the Gaussian filter. The parameters of the filter are such that the width (in seconds) of the Gaussian curve at half the height is equal to the value of Smooth parameter. If Smooth = 0, Gaussian filter is not applied.

import nex
doc = nex.GetActiveDocument()
doc["speed"] = nex.PositionSpeed(doc["LED1_X"], doc["LED1_Y"], 0.1, 0.5)

doc = GetActiveDocument()
doc["speed"] = PositionSpeed(doc["LED1_X"], doc["LED1_Y"], 0.1, 0.5)