HAS-Motion Software Documentation

This page provides an overview of the syntax required to use expressions to their full potential.

Signals from the data tree can be referenced in expressions by using the complete

SIGNAL_TYPE::SIGNAL_FOLDER::SIGNAL_NAME

syntax. To specify a particular element of a signal, e.g. the X Component, simply concatenate the element's name to the end of this:

SIGNAL_TYPE::SIGNAL_FOLDER::SIGNAL_NAME::X

To specify a specific frame from a signal, e.g. Frame 2, use the square bracket notation as follows:

SIGNAL_TYPE::SIGNAL_FOLDER::SIGNAL_NAME[2]

Signals, metrics, and other data stored in the GLOBAL Workspace can be specified by prepending the GLOBAL namespace:

GLOBAL::SIGNAL_TYPE::SIGNAL_FOLDER::SIGNAL_NAME

NOTE: Global data can always be accessed in an Expression regardless of the Active Files.

TARGET::ORIGINAL::RFT1 = Signal RFT1 in the TARGET type and ORIGINAL folder
ANALOG::PROCESSED::FX1 = Signal FX1 in the ANALOG type and PROCESSED folder
PARAMETER::ANALOG::RATE= Parameter RATE in the ANALOG group of the C3D PARAMETERS

Expressions in the Model builder have a simpler syntax because only one version of the metric can exist. In this case, the Type and Folder need not be specified and only the Metric Name is required:

METRIC_NAME

Given 6 markers placed on the surface of a round ball (BALL1, BALL2, BALL3, BALL4, BALL5, BALL6), this example demonstrates how to create a model metric at the centre of a best fit sphere to the ball.

Fill in the the following values in the dialog or pipeline command to create the model metric:

Name = BALL
Expression = Best_Fit_Sphere(List(BALL1, BALL2, BALL3, BALL4, BALL5, BALL6))

The resulting metric will have 3 values separated by a comma, e.g. the 3 components of the center's coordinates. You can create a landmark based on this model metric by using the following syntax:

The syntax may seem a little strange, but [1,1] refers to the first element of the first frame

Model metrics can also be referenced more broadly throughout Visual3D. The following Model data is available to be used in expressions:

MODEL::SEGMENT::segname::LENGTH
MODEL::SEGMENT::segname::DEPTH
MODEL::SEGMENT::segname::CENTER_OF_MASS
MODEL::SEGMENT::segname::IXX
MODEL::SEGMENT::segname::IYY
MODEL::SEGMENT::segname::IZZ
MODEL::SEGMENT::segname::MASS
MODEL::SEGMENT::segname::PROXIMAL_RADIUS
MODEL::SEGMENT::segname::DISTAL_RADIUS
MODEL::SEGMENT::segname::ORIGIN

where “segname” is the name of the segment. Visual3D uses default, 3-letter acronyms for segment names, though these can be modified by the user.

A model's metrics, targets, and landmarks can all be referenced by using the appropriate namespace:

MODEL::METRIC::NAME
MODEL::TARGET::MARKER_NAME
MODEL::LANDMARK::LANDMARK_NAM

As previously, if you want to refer to a specific component of a signal then the component's name can be added to the end of the signal name:

MODEL::TARGET::MARKER_NAME::X

Forces can be referenced using the “FORCE” namespace and will create a global signal containing the average value of the specified FORCE signal over the range of frames specified for the model (e.g. if a range is not specified, all frames will be used).:

MODEL::FORCE::FP1

The command is executed once for each active file, so the resulting signal will continually be overwritten and current results will correspond to the last file processed.

Evaluate_Expression
/EXPRESSION=MODEL::FORCE::FP1
/RESULT_NAME=GLOBAL::SCOTT
/RESULT_TYPE=DERIVED
! /RESULT_FOLDER=PROCESSED
;

The syntax for using a pipeline parameter as part of an expression is a bit unusual and requires an understanding of how Visual3D parses parameters and pre-processes commands.

The ampersand & is used in pipeline commands to concatenate strings together and is therefore a separator for the parser to find the pieces that need to be parsed separately. For example, to use a pipeline parameter LP_FREQ:

/EXPRESSION=2*pi()*&::LP_FREQ

The ampersand tells the parser to take the string “2*pi()*” and the parameter name “::LP_FREQ” separately through the pre-parser. The first part is just taken as is since it is a standard string. The second part is prefixed with “::”, indicating that this is the name of a pipeline parameter.

If you have more complex expressions, you might need to surround each pipeline parameter with an ampersand

&::LP_FREQ&*&::MULTIPLIER&-&::CONSTANT

which may evaluate to something like: 60*1.4-90.0 once all the pipeline parameters are substituted. The general rule to follow is to surround the pipeline parameter with ampersands.

Pipeline parameters and signal definition both use “::” for different purposes. Because of this, and because of the parsing order for expressions, the required syntax for using a pipeline parameter as part of a signal definition is to prefix the pipeline parameter's name with “&:&:&::”.

The following Evaluate_Expression incorporates a pipeline parameter to specify which signals should be subtracted.

Evaluate_Expression
/EXPRESSION=ANALOG::FILTERED&:&:&::INDEX&:&:&X&-METRIC::PROCESSED&:&:&::INDEX&_zero
/RESULT_NAME=::INDEX
/RESULT_TYPE=ANALOG
/RESULT_FOLDER=OFFSET
;

File tags can be included in an expression by prefixing the tag name with the namespace TAG::

TAG::TAG_NAME

C3D parameters can be referenced from the PARAMETER:: namespace and providing both the GROUP and NAME:

PARAMETER::GROUP::PARAMETER_NAME