Calculate Value
Description
Evaluates an algebraic or logical 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, drawing only on tables, lookup tables, and scalar values connected through hooks.
This is one of Dinamica EGO's five calculator functors. Its abbreviated (shorthand) syntax is $. See Calculator functor shorthand in the EGO Script documentation for the verbose and abbreviated forms, and Calculate Functors — Complete Operator Documentation for the full expression language reference.
Inputs
| Name | Type | Description |
|---|---|---|
| Expression | Image Expression Type | Algebraic or logical expression that evaluates to a single numeric result. Must be enclosed in square brackets [ ] in EGO Script. |
Optional Inputs
| Name | Type | Description | Default Value |
|---|---|---|---|
| Default Value | Real Value Type | Value returned if evaluating the expression produces an algebraic error. When not provided, evaluation errors are propagated. This is an advanced port. | .none |
Outputs
| Name | Type | Description |
|---|---|---|
| Result | Real Value Type | The computed scalar value. |
Group
Notes
Connecting data inputs
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 The Expression Language for the complete reference, or Image Expression Type for the navigable operator index.
All operations are performed using the precision defined by ImageExpression::Value; the final result is then converted to a double-precision real. See Calculate Value 2 for a variant that instead performs all operations using double precision throughout.
Null value handling
Null propagation rules and defensive patterns are covered in Null Value Handling in the Calculate Functors documentation.
Internal Name
CalculateValue
Usage examples
- CalculateValue practical examples in the Calculate Functors documentation