Expressions

Many (but not all) edit boxes and pipeline command parameters allow the use of expressions instead of numerical values. Visual3D uses a common expression parser, so the following syntax is common across all command parameters that allow expressions.

Evaluate_Expression Command

The Evaluate_Expression command allows the users to include expressions for defining the processing of the signals.

Evaluate_Expression

/Expression=

!/Signal_Type=

!/Signal_Folder=

!/Signal_Name=

/Result_Type=

/Result_Folder=

/Result_Name=

!/Apply_as_suffix_to_signal_name=FALSE

;

Expression_Items

Data Tree Signals

Expressions_in_Model_Builder_Mode

Pipeline_Parameters

Tags

C3D_Parameters

Model Metrics

String Data

Visual3D Reserved Characters

There are five characters that cause the equation parser considerable trouble. We have introduced reserved pipeline commands that can be used in the place of these characters.

Reserved_Characters
&	Ampersand
:	Colon
;	Semicolon
+	Plus
/	Forward Slash

Visual3D Reserved Names

Reserved_Names
CURRENT_SIGNAL	short hand for signal names
NAN	Not a Number
isNAN	Is Not a Number?

Numbers

Mathematical Constants
pi()	3.14159265358979323846
gravity_vector()	gravity vector in the laboratory coordinate system. For a z-up coordinate system returns (0,0,-9.81)
rand()	Generate a random number

Mathematical Operators

Note: Visual3D parses the mathematical operators before it parses the signal names. If you have a signal name that contains a mathematical operator (e.g. R-Foot1), Visual3D will probably not be able to parse the equation expression properly.

Also Note the potential conflict between some of the operators and the reserved characters. If the string is obviously an expression, there is no conflict.

Mathematical Operators
+	Plus or Add
-	Minus or Subtract
*	Multiply
/	Divide
^	Power -> for example, x^2 = x to the power 2
|	logical OR -> the adjective NOT is allowed
&	logical AND -> the adjective NOT is allowed
== OR =	Equals
<> OR ><	Not Equals
<	Less Than
<= OR =<	Less Than or Equals To
>	Greater Than
>= OR =>	Greater Than or Equals To
NOT()	NOT()

The ugly truth of the logical and

& is used by Visual3D for concatenating strings

it works quite well, but there is one circumstance where this choice of delimiter is a nuisance.

and that is when you want & to actually be a logical and and the parser throws it away

in this case you can use the reserved string AMP

it was only really ugly before version 2024_04 because it didn't work before then

Example given a file that has TAGS labelled TEST1 and TEST2

To select files containing the tags TEST1 and TEST2

Select_Active_File

/FILE_NAME=ALL_FILES

/QUERY=TEST1 & TEST2

! /SUBJECT_TAGS=NO_SUBJECT

;

! But what if you want to generalize and use another pipeline parameter for TEST2

Set_Pipeline_Parameter

/PARAMETER_NAME=SCOTT2

/PARAMETER_VALUE=TEST1 &::AMP &::SCOTT

;

Select_Active_File

/FILE_NAME=ALL_FILES

/QUERY=TEST1 &::AMP &::SCOTT

! /SUBJECT_TAGS=NO_SUBJECT

;

Brackets

Brackets
( )	contain the parameters in a function
[ ]	specify frame numbers and components

Functions

Visual3D has pre-defined functions imbedded in the pipeline to help you out.

These functions are commonly used or have been added based on customer use.

Metric Functions

Metric_Minimum

Metric_Maximum

Metric_Range

Metric_Mean

Metric_Median

Metric_StdDev

Metric_RMS

Metric_Sum

Metric_Integrate

Metric_InterQuartile

Cross_Correlation

Signal Functions

Data Exists

Frame_Count

Add

Sort

Transpose

Interpolate

First Derivative

Second Derivative

Resolve_Discontinuity

Indefinite_Integral

Point_Relative_To_3Points

Snip

Spline

Point_Relative_To_3Points

Append_As

String Data

Specifying String Data

Modifying String Data

Parsing String Data

String_Left

String_Right

String_Mid

String_Find

String_Reverse_Find

String_To_Lower

String_To_Upper

To_String

Least Squares Fitting of Data

Best_Fit_Plane

Best_Fit_Circle

Best_Fit_Sphere

Simple_Linear_Regression

Intersection Functions

Line_Line_Intersect

Line_Plane_Intersect

Project_Point_On_Plane

Point_Distance_To_Plane

Point_Distance_To_Line

Is_Point_Inside_Polygon

Assigned Force Functions

Force

Center Of Pressure

Free Moment

Trigonometric Functions

Cosine

Sine

Tangent

Cotangent

Arctangent

Cosine

Arcsine

ArcCos

Arctan2

Array and Matrix Functions

Vector

Unit_Vector

List

Rotation_Multiply

Rotation_Inverse

Rotation_Transpose

Pose_Euler2Rotation4x4

Common Math Expressions

int(a) - truncate each component to the nearest integer

round(a) - round each component to the nearest integer

fmod(y,x) - Returns the floating-point remainder of y/x

=> y and x must be one dimensional signals; returns a one dimensional signal

abs(a) - absolute value

sign(a)= sign of the signal ((a<0)=-1, (a>0)=1, (a==0) = 0

sqrt(a) - square root

exp(a) - exponent

log(a) - natural log

log10(a) - log base 10

length(x) -- creates the length (magnitude) of a vector

distance(a,b) -- distance between two signals.

Example

Evaluate_Expression

/Expression= distance(LANDMARK::ORIGINAL::RIGHT_HIP , TARGET::ORIGINAL::LHIP)

/Result_Name=PROX_THIGH_RADIUS

! /Result_Type=DERIVED

! /Result_Folder=PROCESSED

;

dot (a, b) -- creates the dot product of a and b

cross (a, b) -- creates the cross product of a and b

NOTE: Often you will want to do dot (a, b)/ length (b), or cross (a, b) / length (b)

Expression Examples

Examples of using Evaluate_Expressions can be found here: Expressions Examples