====== Calculate Map ======

===== Description =====

Computes a new **continuous raster map** by evaluating an algebraic or logical expression independently for every cell in the output map. The expression result is always computed as a real (floating-point) value and then converted to the output map's chosen Cell Type.

This functor is one of five in the [[calculate_functors|calculator family]]. Use it when the expression produces continuous or measured values. If the expression produces integer class codes that should be treated as categories by downstream functors, use [[Calculate Categorical Map]] instead.

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 =====

^ Name ^ Type ^ Description ^
| Expression | [[Image Expression Type]] | The algebraic or logical formula used to compute each output cell. Must be enclosed in square brackets ''[ ]'' in EGO Script. |

===== Optional Inputs =====

^ Name ^ Type ^ Default ^ Description ^
| Cell Type | [[Cell Type Type]] | Signed 32-bit Integer | Data type for each output cell (e.g., byte, int16, float32). |
| Null Value | [[Null Value Type]] | Based on Cell Type | Sentinel value representing "no data" in the output. |
| Result Is Sparse | [[Boolean Value Type]] | False | If true, only non-null cells are stored in memory — saves memory but slows random access. |
| Result Format | [[Map Type]] | None | Optional reference map whose spatial format (extent, resolution, projection) is applied to the output. Category information in the reference map is ignored. Prefer this port over a ''Number Map'' hook when the map is needed only for format purposes — a hook defines an identifier in the expression namespace and blocks abbreviated syntax if that identifier is unused in the expression. |

===== Outputs =====

^ Name ^ Type ^ Description ^
| Result | [[Map Type]] | The computed continuous output map. |

===== Group =====

[[Functor List#Map Algebra | Map Algebra]]

===== Notes =====

==== Connecting data inputs ====

All maps, tables, and scalar values referenced in the expression must be connected to the functor's ports before writing the expression, using **hook** functors:

  * Maps → [[Number Map]] → referenced in the expression as ''i1'', ''i2'', …, ''i100''
  * Tables and lookup tables → [[Number Table]] → referenced as ''t1'', ''t2'', …, ''t100''
  * Scalar values → [[Number Value]] → referenced as ''v1'', ''v2'', …, ''v100''

In the abbreviated syntax, operands are referenced directly by the variable name they are bound to, prefixed with ''#'' for maps, ''%'' for tables, and ''$'' for values — eliminating the hook block entirely.

==== Spatial context and image virtualization ====

The expression is evaluated independently **once per cell** across the output map. Two spatial keywords are available inside the expression:

  * ''line'' — the row index of the current cell, starting at 1
  * ''column'' — the column index of the current cell, starting at 1

When the expression references more than one map, all of them are evaluated at the **same current cell** — ''i1'' and ''i2'' always refer to the same spatial location. Connected maps do **not** need matching extent, resolution, or pixel dimensions: Dinamica EGO reconciles this automatically through **image virtualization**, transparently wrapping each input in a virtual version sharing a common extent and the highest resolution among the inputs. The one requirement that virtualization does not relax is **projection** — all connected maps must share the same projection.

The ''iX[LINE, COL]'' form samples a map at an explicit coordinate rather than the current cell. Coordinates outside the image boundary are **mirrored** back into range. For a row coordinate ''cellLine'' in an image of N rows, ''cellLine'' is normally expected to be in the range [1, N]. When ''cellLine'' is outside this range, it is mirrored back: if ''cellLine'' ≤ 0, the effective row is ''1 − cellLine'' (for instance, ''cellLine'' = 0 → row 1, ''cellLine'' = −1 → row 2, ''cellLine'' = −2 → row 3); if ''cellLine'' > N, the effective row is ''2N + 1 − cellLine'' (for instance, ''cellLine'' = N+1 → row N, ''cellLine'' = N+2 → row N−1, ''cellLine'' = N+3 → row N−2). The same formula applies independently to the column coordinate ''cellCol''. If the target cell is null, the result is 0 rather than null.

==== Available expression features ====

All expression language features are available — there are no restrictions. For the full operator reference, see [[calculate_functors#the_expression_language|The Expression Language]] in the Calculate Functors documentation, or the [[Image Expression Type]] page for the GUI editor and a navigable operator index.

==== Null value handling ====

Null propagation, the two map-calculator exceptions (''iX[LINE, COL]'' returning 0 and neighbourhood functions excluding nulls), and defensive patterns are covered in [[calculate_functors#null_value_handling|Null Value Handling]] in the Calculate Functors documentation. If the computed result exceeds the range of the chosen Cell Type, that cell is also written as null rather than wrapping or clipping.

==== Performance ====

Expression calculations can be compiled to native code automatically (requires the optional native expression support package), delivering near-C performance without any change to the model.

===== Internal Name =====

''CalculateMap''

===== Usage examples =====

  * [[calculate_functors#calculatemap_examples|CalculateMap practical examples]] in the Calculate Functors documentation
  * [[lesson_5|Lesson 5: Implementing a simple map algebra]]