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Defined in: iLand\grid_doc.js:1
Module: iLand

The Grid class encapsulates a floating point grid (with double precision). The class provides high-performance functions for element-wise computations, but also methods for Javascript access. You can load grids from disk (and save to disk), or from iLand by using methods such as Globals.grid, or one of its disturbance submodules (e.g., Barkbeetle/grid:method, Wind/grid:method). The extent and cell size depend on the respective functions, but usually cover the whole landscape.

Use apply for updating a single grid, and combine for calculating grid values based on combining multiple grid sources.

Javacsript based access to grid values is possible via value and setValue methods ( valueAt and setValueAt for access by coordinates).

Memory management

Methods such as Globals.grid return a copy of the data present in iLand, and calls to apply or combine alter the underlying data; you can use the copy method create a duplicate grid (if the underlying data should not change). Memory of grids is freed automatically by the Javascript engine (garbage collection) when they are no longer referenced.

Coordinate system

Grids use the local coordiante system of iLand, i.e. the point (0,0) is the lower left corner of the project area. When grids are loaded from disk, the coordinates are transformed to that system (relative to the world.location.x and world.location.y settings in the iLand project file). For example, consider a iLand local system with an origin of (12650, 4500). Now, consider loading a grid with the origin (14000,5000) (i.e, xllcorner, yllcorner) and a cellsize of 100m. The iLand coordiantes (0/0) would then be invalid, and the lower left pixel of the grid can be accessed with, e.g., value(1420, 550).

Examples

// memory management
var g=Globals.grid('height');
g.apply('height*2'); // modify 'g'
var h=g.copy();
h.apply('x*2'); // modify copy of 'g'

Methods

aggregate

(
  • factor
)

Aggregates the grid by averaging over multiple cells. This changes the resolution of the underlying grid by a factor factor (e.g., aggregating a 10m grid with factor=4 results in a grid with 40m resolution). The value of the target cell is the average over source cells. Note: no special care is taken for -1 values.

Parameters:

  • factor Int

    multiplier for target cell size

apply

(
  • expression
)

Apply a function on the values of the grid, thus modifiying the grid (see the copy() function). The function is given as a string representing an Expression and is evaluated for each cell of the grid. In the expression, the current value of the grid cell can be accessed using the name.

See also: copy, combine

Parameters:

  • expression String

    expression that is applied to each cell of the grid

Example:

var g = Globals.grid('height'); // name is 'height'
                    g.apply('x*x'); // error, invalid variable
                    g.apply('min(height, 30'); // ok
                    g.apply('if(height<=4, 0, height)'); // ok
                    var h = g.copy();
                    h.apply('x^2'); // use copy() if the grid should not change (note: copies are named 'x')

clear

()

Fill the grid with 0-values.

combine

(
  • expression
  • grid_objects
)

Combine multiple grids, and set the value of the internal grid to the result of expression for each cell. The function expects an object that includes named source grids. The expression is an iLand Expression, and you can refer to the grids in grid_objects with the respective name of the grid. Note that the function alters the data of the grid.

All grids must have the same dimensions, and the grid iteself can be accessed by adding the grid to grid_objects.

See also: copy, apply

Parameters:

  • expression String

    expression that is applied to each cell of the grid

  • grid_objects Object

    object including the source grids; the individual grids are provided as name-value pairs and the provided names are the variable names in the expression (see example).

Example:

var g = Globals.grid('height'); // name of g is 'height'
                    var j = Globals.grid('count');
                    var k = g.copy();
                    k.apply('if(height>30,1,0)');
                    // update 'k' by combining g,j, and k
                    k.combine('height*count * filter', { height: g, filter: k, count: j } ); // access grid 'g' as 'height', grid 'k' as 'filter', grid 'j' as count in the expression

copy

() Grid

Create a copy of the current grid and return a new grid object. The name of the copied grid is x. Memory management is automatic (garbage collection), i.e. you don't have to worry about freeing the memory.

Returns:

Grid:

a copy of the grid

Example:

var a = Globals.grid('height');
                    var ac = a.copy();
                    ac.name = 'h2'; // change the name

create

(
  • width
  • height
  • cellsize
)
Boolean

Creates a numeric grid (floating point) with the dimensions width and height with the cell size cellsize and fills the grid with 0. The grid is located at the origin of the project area (i.e., at coordiantes (0,0)). No clipping is applied.

Note that the grid object must already exist! Use newGrid to create a new grid from scratch, or other functions that return grids (e.g., copy, grid ).

See also: load, setOrigin, newGrid

Parameters:

  • width Int

    the number of cells in x-direction

  • height Int

    the number of cells in y-direction

  • cellsize Int

    the cellsize (m)

Returns:

Boolean:

true on success.

Example:

var g = Factory.newGrid(); // create a grid
                    g.create(10,20,5); // populate with an empty grid with 50x100m
                    g.setValue(4,5,-1); // modify the grid
                    g.setOrigin(1000, 1000); // move the grid (the lower left corner) to the given coordinates
                    g.save("test.txt"); // save as ESRI raster file
                    

info

() String

Retrieve some key parameters of the grid as a string.

Returns:

String:

the information string

Example:

var g = Globals.grid('height');
                    console.log(g.info());
                    //prints:  grid-dimensions: 1820/1020 (cellsize: 10, N cells: 1856400), grid-name='height'

load

(
  • file_name
)
Boolean

Load from a file file_name (ESRI ASCII raster grid). The name property is set to the base file name (without path and extension).

See also: save

Parameters:

  • file_name String

    source file name (relative to project folder)

Returns:

Boolean:

true on success.

load

(
  • fileName
)
Boolean

load loads a grid in ESRI ASCII format. The grid internally uses floating point precision. Furthermore, the grid is aligned to the iLand project area, but not clipped and the cellsize is retained (contrary to the MapGrid, which clips the grid to the project area and resamples the content of the grid to a cellsize of 10m).

See also: create, setOrigin

Parameters:

  • fileName String

    the filename of the grid; paths are relatve to the root folder of the project.

Returns:

Boolean:

returns true on success

Example:

var g = Factory.newGrid(); // create a grid
                    g.load('gis/biggrid.asc'); // load the raster file
                    

resample

(
  • target_grid
)

Resamples the content of the current grid to the extent/cellsize given by the grid target_grid. If target_grid is larger than the current grid 0-values are inserted, otherwise the grid is cropped to target_grid.

Resampling is "brute-force", every cell of the new grid is set to the value that the current grid has at the new cell's center (i.e. no interpolation takes place). Resampling alters the current grid.

Parameters:

  • target_grid Object

    Grid with target extent and resolution

save

(
  • file_name
)

Save to a file file_name as ESRI ASCII raster file.

See also: load

Parameters:

  • file_name String

    destination file name (relative to project folder)

setOrigin

(
  • x
  • y
)

setOrigin updates the origin of the grid, effectively moving the grid to a new position relative to the origin of the project area.

Note, that no additional checks are performed - use with care.

See also: create, load

Parameters:

  • x Double

    new value for the x-coordinate of the origin

  • y Double

    new value for the y-coordinate of the origin

Example:

var g = Factory.newGrid(); // create a grid
                    g.create(10,20,5); // populate with an empty grid with 50x100m
                    g.setValue(4,5,-1); // modify the grid
                    g.setOrigin(1000, 1000); // move the grid (the lower left corner) to the given coordinates
                    g.save("test.txt"); // save as ESRI raster file
                    

setValue

(
  • x
  • y
  • value
)

Set the value at position (x, y) to value. Note that using the value and setValue methods is much slower than using functions such as apply.

See also: value

Parameters:

  • x Integer

    index in x direction (between 0 and grid.width-1)

  • y Integer

    index in y direction (between 0 and grid.height-1)

  • value Double

    value to set

Example:

// using javascript access functions can be 100x times slower:
                    var g = Globals.grid('height');
                    var ela=Globals.msec; // for measuring time, see also the 'msec' doc
                    
                    for (var i=0;i<g.width;++i) {
                        for (var j=0;j<g.height;++j) {
                            g.setValue(i,j, g.value(i,j)*2);
                        }
                    }
                    console.log("javascript: " + (Globals.msec - ela) + "ms"); // 1650ms
                    ela = Globals.msec;
                    g.apply('height*2');
                    console.log("apply(): " + (Globals.msec - ela) + "ms"); // 17ms
                    

setValueAt

(
  • x
  • y
  • value
)

Set the value at the coordinates (x, y) to value. Note that using the value and setValue methods is much slower than using functions such as apply.

The coordinates are relative to the iLand project area.

See also: value

Parameters:

  • x Double

    index in x direction (between 0 and grid.width-1)

  • y Double

    index in y direction (between 0 and grid.height-1)

  • value Double

    value to set

Example:

// using javascript access functions can be 100x times slower:
                    var g = Globals.grid('height');
                    var ela=Globals.msec; // for measuring time, see also the 'msec' doc
                    
                    for (var i=0;i<g.width;++i) {
                        for (var j=0;j<g.height;++j) {
                            g.setValue(i,j, g.value(i,j)*2);
                        }
                    }
                    console.log("javascript: " + (Globals.msec - ela) + "ms"); // 1650ms
                    ela = Globals.msec;
                    g.apply('height*2');
                    console.log("apply(): " + (Globals.msec - ela) + "ms"); // 17ms
                    

sum

(
  • expresion
)
Double

Apply the expression expression on all pixels of the grid and return the sum of the values

See also: apply

Parameters:

  • expresion String

    expression to evaluate

Returns:

Double:

sum of expression over all cells

Example:

var g = Globals.grid('height');
                    var mean_h = g.sum('height') / g.count;
                    g.apply('height/' + mean_h); // scale the height grid

value

(
  • x
  • y
)
Double

Access individual cell values of the grid at the given position. If the grid is empty, or the the given position is invalid, -1 is returned.

See also: setValue

Parameters:

  • x Integer

    index in x direction (between 0 and grid.width-1)

  • y Integer

    index in y direction (between 0 and grid.height-1)

Returns:

Double:

value of the grid at position (x, y)

valueAt

(
  • x
  • y
)
Double

Access individual cell values of the grid at the given metric coordinates. If the grid is empty, or the the given position is invalid, -1 is returned. The coordiantes are relative to the origin of the iLand project area.

See also: setValue

Parameters:

  • x Double

    coordinate (m)

  • y Double

    coordinate (m)

Returns:

Double:

value of the grid at position (x, y)

Properties

cellsize

Integer

the cell size of the grid in meters.

See also: count, height, width

count

Integer

the number of pixels of the grid.

See also: cellsize, height, width

height

Integer

the height (y-dimension) of the grid (number of pixels)

See also: cellsize, width

isValid

Boolean

is true if the grid contains data.

name

String

gets or sets the name of the grid (that are used for calculations)

width

Integer

the width (x-dimension) of the grid (number of pixels)

See also: cellsize, height