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calculate_map [2013/08/13 20:03] admin [Notes] |
calculate_map [2026/07/15 01:17] (current) hermann |
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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 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. | ||
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| + | 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 output map. | | + | | 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 ===== | ===== Optional Inputs ===== | ||
| - | ^ Name ^ Type ^ Description ^ Default Value ^ | + | ^ Name ^ Type ^ Default ^ Description ^ |
| - | | Cell Type | [[Cell Type Type | Cell Type]] | Data cell type | Signed 32 Bit Integer | | + | | 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 | Null Value]] | Null value | Default((Based on the value of the Cell Type input.)) | | + | | Null Value | [[Null Value Type]] | Based on Cell Type | Sentinel value representing "no data" in the output. | |
| - | | 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]] | False | If true, only non-null cells are stored in memory — saves memory but slows random access. | |
| - | | Result Format | [[Map Type| Map]] | Map representing the output format. Any category information presents in the given map is not used as part of the map format. | None | | + | | 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 ===== | ===== Outputs ===== | ||
| - | ^ Name ^ Type ^ Description ^ | + | ^ Name ^ Type ^ Description ^ |
| - | | Result | [[Map Type | Map]] | Output map. | | + | | Result | [[Map Type]] | The computed continuous output map. | |
| ===== 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, the corresponding cell is filled with the null value. In practice, it means that every time a null value is found in a expression calculation, the calculation results in null value, unless the occurrence of the null value is isolated from the rest of the expression by a special operator like ''[[image_expression_type#image_operators_and_functions|isNull()]]'' or ''[[image_expression_type#general_operators|?]]''. | + | 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: |
| - | The examples below illustrates: | + | * 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'' | ||
| - | ^ Example ^ Analysis ^ | + | 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. |
| - | | <code cpp>i1 / 0</code> | The expression always results in null value. | | + | |
| - | | <code cpp>i1 + i2 / i3 ^ 3</code> | If the current cell of any of the images involved in the calculation is null value, the expression results in null value . | | + | |
| - | | <code cpp>if isNull(i1) then | + | |
| - | 1 | + | |
| - | else | + | |
| - | 2 | + | |
| - | </code> | The expression never results in null value. | | + | |
| - | | <code cpp>if isNull(i1) then | + | |
| - | i2 | + | |
| - | else | + | |
| - | i3 | + | |
| - | </code> | The expression might result in null value depending on the the value of i2 and i3. | | + | |
| - | | <code cpp>(100 / i2) ? 0</code> | The expression never results in null value. | | + | |
| - | | <code cpp>(100 / i2) ? i1</code> | The expression might result in null value depending on the the value of i1. | | + | |
| - | If the data cell type is not large enough, the corresponding cell is also filled with the null value. | + | ==== Spatial context and image virtualization ==== |
| - | 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]]. | + | 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. | ||
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| + | ==== 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. | ||
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| + | ==== 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. | ||
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| + | ==== 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. | ||
| - | The maps used by the "Calculate Map" must be provided by a corresponding [[Number Map]], the tables must be provided by a corresponding [[Number Table]] and the values must be provided by a corresponding [[Number Value]]. | ||
| ===== Internal Name ===== | ===== Internal Name ===== | ||
| - | CalculateMap | + | ''CalculateMap'' |
| + | |||
| + | ===== Usage examples ===== | ||
| + | |||
| + | * [[calculate_functors#calculatemap_examples|CalculateMap practical examples]] in the Calculate Functors documentation | ||
| + | * [[lesson_5|Lesson 5: Implementing a simple map algebra]] | ||