Calculate Value

Description

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 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 Calculator functor shorthand in the EGO Script documentation for the full syntax of both the verbose and abbreviated forms, and Calculate Functors — Complete Operator Documentation for the complete expression language reference.

Inputs

Name	Type	Description
Expression	Image Expression Type	The algebraic or logical formula that evaluates to a single numeric result, written using the image expression editor. Must be enclosed in square brackets [ ] in EGO Script.

Optional Inputs

Name	Type	Default	Description
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.

Output

Name	Type	Description
Result	Real Value Type	The computed scalar value.

Group

Table

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.

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

Lesson 8: Inserting and getting a specific value into a table