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.

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
;

Expressions are incredibly flexible and capable of ingesting most data types in Visual3D. The key to using expressions is to understand the syntax used for each data type:

1. Data Tree Signals
2. In Model Builder mode
3. Model Metrics
4. Pipeline Parameters
5. File Tags
6. C3D Parameters
7. String Data

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

We have introduced reserved names for a few common ideas that are useful to reference in constructing expressions.

We have introduced three number-related functions to aid in the construction of expressions.

In its simplest use, the Evaluate_Expression command can be used to evaluate arbitrary mathematical expressions. Use the following characters for your 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.

The & character is used by Visual3D for concatenating strings. This works quite well, but there is one circumstance where this choice of delimiter is a nuisance. That is when you want & to actually be a logical AND and the parser throws it away.

As of v2024.04.1 you can use the reserved string AMP for these cases.

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
;

Visual3D has pre-defined functions embedded in the pipeline to help you construct your expressions. These functions are commonly used or have been added based on customer use.

• Metric_Minimum
• Metric_Maximum
• Metric_Range
• Metric_Mean
• Metric_Median
• Metric_StdDev
• Metric_RMS
• Metric_Sum
• Metric_Integrate
• Metric_InterQuartile
• Cross_Correlation

• Data Exists
• Frame_Count
• Add
• Sort
• Transpose
• Interpolate
• First Derivative
• Second Derivative
• Resolve_Discontinuity
• Indefinite_Integral
• Cumulative_Sum
• Point_Relative_To_3Points
• Point_Tracked_By_3Points
• Snip
• Spline
• Append_As

• 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

• Best_Fit_Plane
• Best_Fit_Circle
• Best_Fit_Sphere
• Simple_Linear_Regression

• Line_Line_Intersect
• Line_Plane_Intersect
• Project_Point_On_Plane
• Point_Distance_To_Plane
• Point_Distance_To_Line
• Is_Point_Inside_Polygon

• Force
• Center Of Pressure
• Free Moment

• Cosine
• Sine
• Tangent
• Cotangent
• Arctangent
• Cosine
• Arcsine
• ArcCos
• Arctan2

• Vector
• Unit_Vector
• List
• Rotation_Multiply
• Rotation_Inverse
• Rotation_Transpose
• Pose_4x4

• 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 (Note: 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.
• dot (a, b) – creates the dot product of a and b
• cross (a, b) – creates the cross product of a and b

Examples of using Evaluate_Expressions can be found here: Expressions Examples