A custom measure is defined by a string formula that can use other custom or predefined measure. It must have a unique name.

SoDataMeasureCustom* myMeasure1 = new SoDataMeasureCustom();
myMeasure1->measureName = "myMeasure1";
myMeasure1->formula = SoDataMeasurePredefined.getName(SoDataMeasurePredefined.VOLUME) + "/" + SoDataMeasurePredefined.getName(SoDataMeasurePredefined.AREA);

SoDataMeasureCustom* myMeasure2 = new SoDataMeasureCustom();
myMeasure2->measureName = "myMeasure2";
myMeasure2->formula = myMeasure1.getMeasureName() + "*2";

Custom formula syntax

Custom formula syntax is checked before acceptation by ImageViz. Custom measure formula and custom filter formula follow the same basic rules and can use the same set of predefined functions. Custom measure formula must be a numerical value whereas custom filter formula must be a logical value to be accepted. Formula can be composed of constants, operators, functions and variables (native measures and custom measures).

Remarks :

• The following (unless specified) constants, operators, functions and variables are unsensitive to case and can be used both with custom measures and custom filters.

• The following (unless specified) operators and functions are unsensitive to spaces. Constants and variables must not be directely attached to alpha numerical symbols.

The following syntax can be used to define a formula :

Basic operators

() : brackets allowing to group elements and to modify operators precedence example : (2 + 3)*4

+ : unary arithmetic operator [plus] example : + a

- : unary arithmetic operator [minus] example : - b

+ : binary arithmetic operator [plus] example : a + b

- : binary arithmetic operator [minus] example : a - b

* : binary arithmetic operator [multiply] example : a * b

/ : binary arithmetic operator [divide] example : a / b remark : a division by 0 returns the value 0 in order to avoid exceptions.

** : binary arithmetic operator [pow] example : a ** b

! : unary logical operator [not] example : !(a>b)

&& : or And : binary logical operator [and] example : (a>b) && (a<c) example : (a>c) And (a<c) remark : And : operator must not be directely attached to alpha numerical symbols.

|| : or Or : binary logical operator [or] example : (a>b) || (a<c) example : (a>b) Or (a<c) remark : Or : operator must not be directely attached to alpha numerical symbols.

== : comparison operator (logical and arithmetic) [equal] example : a==b example : true==true

!= : comparison operator (logical and arithmetic) [different] example : a != b example : true != false

< : arithmetic comparison operator [strictly inferior] example : a < b

<= : arithmetic comparison operator [less] example : a<= b

> : arithmetic comparison operator [strictly superior] example : a > b

>= : arithmetic comparison operator [superior] example : a >= b

Constant values

Pi : , the pi constant example : 3 * Pi

E : , the Euler's constant example : 2 * E

True : the true boolean value example : (3<Pi)==True

False : the false boolean value example : (3>Pi)==False

NbFeret : distribution size for feret measures example : 3*NbFeret

gx : , gy : and gz : image X, Y and Z size associated to measure example : 3*gx remark : not available for custom filters

cx : , cy : and cz : stand for pixel real size according to calibration example : 3*cx remark : not available for custom filters

Functions

Abs : absolute value of a numerical value example : abs(a)

Sqrt : square root value of a numerical value example : sqrt(a) remark : a must be positive or null

Exp : exponential value of a numerical value example : exp(a)

Log : natural logarithm value of a numerical value example : log(a) remark : a must be strictly positive

Cos : cosine value of a numerical value example : cos(a)

Sin : sine value of a numerical value example : sin(a)

Tan : tangent value of a numerical value example : tan(a)

ACos : arccosine value of a numerical value example : acos(a) remark : a must within range [-1, 1]

ASin : sine arcvalue of a numerical value example : asin(a) remark : a must within range [-1, 1]

ATan : arctangent value of a numerical value example : atan(a)

ATan2 : arctangent value of a 2d point example : atan(y, x)

CosH : hyperbolic cosine value of a numerical value example : cosh(a)

SinH : hyperbolic sine value of a numerical value example : sinh(a)

TanH : hyperbolic tangent value of a numerical value example : tanh(a)

Min : retrieve minimum value of a variable sized set of numerical values example : min(a, b, c, d)

Max : retrieve maximum value of a variable sized set of numerical values example : max(a, b, c, d, e)

Avg : retrieve mean value of a variable sized set of numerical values example : avg(a, b, c)

Median : retrieve median value of a variable sized set of numerical values example : median(a, b, c, d)

Sum : compute the sum of a variable sized set of numerical values example : sum(a, b, c)

Sum : compute the product of a variable sized set of numerical values example : product(a, b, c, d, e)

If : : conditional evaluation of an expression example : if(predicat, value_true, value_false) remark : Each member of a conditional expression is systematically evaluated even if it is not supposed to be reached by the condition. Thus an instruction can raise an error even if the condition is supposed to prevent invalid evaluations. example: if(I1<=0, 0, log(I1)) will raise an error if a voxel value is lower or equal to 0 since the log expression will be evaluated before the if statement.

Reference