The Grid Calculator calculates a new grid based on existing grids and a mathematical formula. The grid variables in the formula begin with the letter 'g' followed by a position index, which corresponds to the order of the grids in the input grid list (i.e.: g1, g2, g3, ... correspond to the first, second, third, ... grid in list). Grids from other systems than the default one can be addressed likewise using the letter 'h' (h1, h2, h3, ...), which correspond to the 'Grids from different Systems' list.
Example: sin(g1) * g2 + 2 * h1
To make complex formulas look more intuitive you have the option to use shortcuts. Shortcuts are defined following the formula separated by semicolons as 'shortcut = expression'.
Example: ifelse(lt(NDVI, 0.4), nodata(), NDVI); NDVI = (g1 - g2) / (g1 + g2)
The following operators are available for the formula definition:
| + | Addition |
| - | Subtraction |
| * | Multiplication |
| / | Division |
| abs(x) | Absolute Value |
| mod(x, y) | Returns the floating point remainder of x/y |
| int(x) | Returns the integer part of floating point value x |
| sqr(x) | Square |
| sqrt(x) | Square Root |
| exp(x) | Exponential |
| pow(x, y) | Returns x raised to the power of y |
| x ^ y | Returns x raised to the power of y |
| ln(x) | Natural Logarithm |
| log(x) | Base 10 Logarithm |
| pi() | Returns the value of Pi |
| sin(x) | Sine, expects radians |
| cos(x) | Cosine, expects radians |
| tan(x) | Tangent, expects radians |
| asin(x) | Arcsine, returns radians |
| acos(x) | Arccosine, returns radians |
| atan(x) | Arctangent, returns radians |
| atan2(x, y) | Arctangent of x/y, returns radians |
| min(x, y) | Returns the minimum of values x and y |
| max(x, y) | Returns the maximum of values x and y |
| gt(x, y) | Returns true (1), if x is greater than y, else false (0) |
| x > y | Returns true (1), if x is greater than y, else false (0) |
| lt(x, y) | Returns true (1), if x is less than y, else false (0) |
| x < y | Returns true (1), if x is less than y, else false (0) |
| eq(x, y) | Returns true (1), if x equals y, else false (0) |
| x = y | Returns true (1), if x equals y, else false (0) |
| and(x, y) | Returns true (1), if both x and y are true (i.e. not 0) |
| or(x, y) | Returns true (1), if at least one of both x and y is true (i.e. not 0) |
| ifelse(c, x, y) | Returns x, if condition c is true (i.e. not 0), else y |
| rand_u(x, y) | Random number, uniform distribution with minimum x and maximum y |
| rand_g(x, y) | Random number, Gaussian distribution with mean x and standard deviation y |
| xpos(), ypos() | The coordinate (x/y) for the center of the currently processed cell |
| col(), row() | The currently processed cell's column/row index |
| ncols(), nrows() | Number of the grid system's columns/rows |
| nodata(), nodata(g) | No-data value of the resulting (empty) or requested grid (g = g1...gn, h1...hn) |
| cellsize(), cellsize(g) | Cell size of the resulting (empty) or requested grid (g = h1...hn) |
| cellarea(), cellarea(g) | Cell area of the resulting (empty) or requested grid (g = h1...hn) |
| xmin(), xmin(g) | Left bound of the resulting (empty) or requested grid (g = h1...hn) |
| xmax(), xmax(g) | Right bound of the resulting (empty) or requested grid (g = h1...hn) |
| xrange(), xrange(g) | Left to right range of the resulting (empty) or requested grid (g = h1...hn) |
| ymin(), ymin(g) | Lower bound of the resulting (empty) or requested grid (g = h1...hn) |
| ymax(), ymax(g) | Upper bound of the resulting (empty) or requested grid (g = h1...hn) |
| yrange(), yrange(g) | Lower to upper range of the resulting (empty) or requested grid (g = h1...hn) |
| zmin(g) | Minimum value of the requested grid (g = g1...gn, h1...hn) |
| zmax(g) | Maximum value of the requested grid (g = g1...gn, h1...hn) |
| zrange(g) | Value range of the requested grid (g = g1...gn, h1...hn) |
| zmean(g) | Mean value of the requested grid (g = g1...gn, h1...hn) |
| zstddev(g) | Standard deviation of the requested grid (g = g1...gn, h1...hn) |
| | Name | Type | Identifier | Description | Constraints |
|---|
| Input | Grids | grid list, input, optional | GRIDS | in the formula these grids are addressed in order of the list as 'g1, g2, g3, ...' | - |
| Grids from different Systems | grid list, input, optional | XGRIDS | in the formula these grids are addressed in order of the list as 'h1, h2, h3, ...' | - |
| Output | Result | grid, output | RESULT | - | - |
| Options | Grid System | grid system | PARAMETERS_GRID_SYSTEM | - | - |
| Resampling | choice | RESAMPLING | - | Available Choices:
[0] Nearest Neighbour
[1] Bilinear Interpolation
[2] Bicubic Spline Interpolation
[3] B-Spline Interpolation
Default: 3 |
| Formula | text | FORMULA | - | Default: (g1 - g2) / (g1 + g2) |
| Use No-Data | boolean | USE_NODATA | Check this in order to include no-data cells in the calculation. | Default: 0 |
| Data Type | data type | TYPE | - | Available Choices:
[0] bit
[1] unsigned 1 byte integer
[2] signed 1 byte integer
[3] unsigned 2 byte integer
[4] signed 2 byte integer
[5] unsigned 4 byte integer
[6] signed 4 byte integer
[7] unsigned 8 byte integer
[8] signed 8 byte integer
[9] 4 byte floating point number
[10] 8 byte floating point number
Default: 9 |