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calculate_value [2011/07/26 19:23]
hermann created 		calculate_value [2026/07/07 16:11] (current)
hermann
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-====== Calculate Value ====== ​+====== Calculate Value ======
  
 ===== Description ===== ===== Description =====
  
-This container calculates ​a value employing ​a logic/​algebraic ​expression.+Evaluates an expression **once** and returns a single **scalar value**. Unlike the map and lookup table calculators,​ there is no current cell, row, or spatial grid — the expression is evaluated in a purely scalar context. 
 + 
 +This functor is one of five in the [[calculate_functors|calculator family]]. Use it to compute a single parameter — such as a global threshold, a weighted sum of scalar inputs, or a value derived from a table — that can then be passed as input to other functors. 
 + 
 +The **abbreviated syntax** (also called **shorthand**) for this functor is ''​$''​. See [[ego_script#​calculator_functor_shorthand|Calculator functor shorthand]] in the EGO Script documentation for the full syntax of both the verbose and abbreviated forms, and [[calculate_functors|Calculate Functors — Complete Operator Documentation]] for the complete ​expression ​language reference.
  
 ===== Inputs ===== ===== Inputs =====
  
-^ Name            ^ Type                                              ^ Description ​                              ​^ +^ Name ^ Type ^ Description ^ 
-| Expression ​     | [[Image Expression Type|Image Expression  ​]]      | Algebraic ​or logical ​expression used to calculate the lookup table. |+| Expression | [[Image Expression Type]] | The algebraic ​or logical ​formula that evaluates ​to a single numeric result. Must be enclosed in square brackets ''​[ ]''​ in EGO Script. |
  
 ===== Optional Inputs ===== ===== Optional Inputs =====
  
-^ Name              ^ Type                      ^ Description ​                                                                                                                                      ^ Default Value ^ +^ Name ^ Type ^ Default ​^ Description ^ 
-| Use Default Value | [[Bool Type|Bool  ​]]      | If true, a default value will be passed as an output of the algebraic/​logic ​expression ​in case an algebraic error occurs, e.g. division by zero.  | False         | +| Default Value | [[Real Value Type]] | None | Value returned if the expression ​produces ​an algebraic error. When provided, acts as a catch-all fallback equivalent ​to wrapping the entire expression ​in the ''?''​ operator. |
-| Default Value     | [[Double Type|Double ​ ]]  | Value to be passed ​in case an algebraic error occurs.                                                                                             ​| 0.0           | +
  
 ===== Output ===== ===== Output =====
  
-^ Name       ​^ Type                      ^ Description ​          ​^ +^ Name ^ Type ^ Description ^ 
-| Calculated ​| [[Double ​Type|Double  ​]]  | The calculated ​value. |+| Result ​| [[Real Value Type]] | The computed scalar ​value. |
  
 ===== Group ===== ===== Group =====
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 ===== Notes ===== ===== Notes =====
  
-The list of mathematical and logical operators that can be employed in the logic/​algebraic expression can be found in the [[Image Expression Type | image expression reference]]. Note that the operators and functions described in [[Image Expression Type#Image Operators and Functions | Image Operators and Functions]] ​ and [[Image Expression Type#Image Neighborhood Functions +==== Connecting data inputs ====
-| Image Neighborhood Functions]] can not be used in value calculations.+
  
-The tables ​used by the "​Calculate Lookup Table" ​must be provided by a corresponding ​[[Number Table]] ​and the values ​must be provided by a corresponding ​[[Number Value]].+Tables, lookup ​tables, and scalar values referenced in the expression ​must be connected to the functor'​s ports before writing the expression, using **hook** functors: 
 + 
 +  * Tables and lookup tables → [[Number Table]] ​→ referenced in the expression as ''​t1'',​ ''​t2'',​ …, ''​t100''​ 
 +  * Scalar ​values ​→ [[Number Value]] ​→ referenced as ''​v1'',​ ''​v2'',​ …, ''​v100''​ 
 + 
 +Maps cannot be connected — there is no cell context in this functor. In the abbreviated syntax, tables are referenced as ''​%variableName''​ and values as ''​$variableName''​. 
 + 
 +==== Available expression features ==== 
 + 
 +Image operators (''​iX''​),​ the ''​line''​ and ''​column''​ spatial keywords, neighbourhood functions, neighbourhood indexing, and convolution are not available — there is no cell or row context. Available features are arithmetic and logical operators and table and lookup table queries (''​tX[...]''​) in all single-key and multi-column forms. See [[calculate_functors#​the_expression_language|The Expression Language]] for the complete reference, or [[Image Expression Type]] for the navigable operator index. 
 + 
 +==== Null value handling ==== 
 + 
 +Null propagation rules and defensive patterns are covered in [[calculate_functors#​null_value_handling|Null Value Handling]] in the Calculate Functors documentation.
  
 ===== Internal Name ===== ===== Internal Name =====
  
-CalculateValue+''​CalculateValue''​ 
 + 
 +===== Usage examples ===== 
 + 
 +  * [[calculate_functors#​calculatevalue_examples|CalculateValue practical examples]] in the Calculate Functors documentation 
 +  * [[lesson_8|Lesson 8: Inserting and getting a specific value into a table]]