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calculate_map [2011/07/25 01:10]
hermann 		calculate_map [2026/08/28 03:14] (current)
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 ===== Description ===== ===== Description =====
  
-This container calculates ​a map using algebraic/logical expression ​involving maps, tables ​and values.+Computes ​a new continuous raster ​map by evaluating an algebraic ​or logical expression ​independently for every cell of 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. Use this functor when the expression produces continuous or measured ​values; use [[Calculate Categorical Map]] instead when the expression produces integer class codes that downstream functors should treat as categories. 
 + 
 +This is one of Dinamica EGO's five calculator functors. Its abbreviated (shorthand) syntax is ''#''​. See [[ego_script#​calculator_functor_shorthand|Calculator functor shorthand]] in the EGO Script documentation for the verbose and abbreviated forms, and [[Calculate Functors|Calculate Functors — Complete Operator Documentation]] for the full 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 output ​map. |+| Expression ​ | [[Image Expression Type]] ​ | Algebraic or logical ​formula ​used to compute each output ​cell. Must be enclosed in square brackets ''​[ ]''​ in EGO Script.  |
  
 ===== Optional Inputs ===== ===== Optional Inputs =====
  
-^ Name             ​^ Type                           ​^ Description ​                                                                                                                                                                          ​^ Default Value         ​^ +^ Name  ^ Type  ^ Description ​ ^ Default Value  ^ 
-| Cell Type        | [[Cell Type Type | Cell Type]] | Data cell type                                                                                                                                                                        | Signed 32 Bit Integer | +| Cell Type  | [[Cell Type Type]] ​ | Data type for each output cell.  ​| Signed 32 Bit Integer ​ | 
-| Null Value       ​| [[Int Type | Int]]             ​| Null value                                                                                                                                                                            | -2147483648 ​          | +| Null Value  | [[Null Value Type]] ​ | Sentinel ​value representing "no data" in the output.  ​| .default  ​| 
-| Result Is Sparse | [[Bool Type | Bool]]           ​| If true, the resulting map is created as a sparse image. Sparse images have the advantage of storing ​only the cells containing ​non-null ​values, but they have diminished ​access ​time. | False                 |+| Result Is Sparse ​ | [[Boolean Value Type]] ​ | If true, only non-null ​cells are stored, saving memory at the expense of random-access ​speed. This is an advanced port.  ​| No  | 
 +| Result Format ​ | [[Map Type]] ​ | Reference map whose spatial format (extent, resolution, projection) is applied to the output; its category information,​ if any, is ignored. Prefer this port over a Number Map hook when a map is needed only for format purposes, since a hook defines an identifier in the expression namespace and blocks abbreviated syntax if that identifier goes unused in the expression. This is an advanced port.  | .none  ​|
  
 ===== Outputs ===== ===== Outputs =====
  
-^ Name   ​^ Type               ​^ Description ^ +^ Name  ^ Type  ^ Description ​ ^ 
-| Result | [[Map Type | Map]] | Output ​map. |+| Result ​ | [[Map Type]] ​ | Computed output ​map. Its dimensions come from the connected input maps, or from Result Format when given.  ​|
  
 ===== Group ===== ===== Group =====
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 ===== Notes ===== ===== Notes =====
  
-The expression result is calculated as a real value and converted to the data cell type of the output map.+==== Connecting ​data inputs ====
  
-If the calculation ​of the expression ​diverges ​or if the data cell type is not large enough, the corresponding ​cell is filled with the null value.+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.
  
-A 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]]. 
-  
 ===== Internal Name ===== ===== Internal Name =====
  
 CalculateMap CalculateMap
 +
 +===== Usage examples =====
 +
 +  * [[Calculate Functors#​CalculateMap practical examples|CalculateMap practical examples]] in the Calculate Functors documentation
 +  * [[lesson_5|Lesson 5: Implementing a simple map algebra]]