The iLand Javascript API
Grid Class
iLand\grid_doc.js:1
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. To view the content of the grid visually,
use the registerUI method.
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'Item Index
Methods
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:
-
factorIntmultiplier 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.
Parameters:
-
expressionStringexpression 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.
Parameters:
-
expressionStringexpression that is applied to each cell of the grid
-
grid_objectsObjectobject 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 expressioncopy
()
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:
a copy of the grid
Example:
var a = Globals.grid('height');
var ac = a.copy();
ac.name = 'h2'; // change the namecreate
-
width -
height -
cellsize
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 new Grid() to create a new grid from scratch, or other functions
that return grids (e.g., copy, grid ).
Parameters:
-
widthIntthe number of cells in x-direction
-
heightIntthe number of cells in y-direction
-
cellsizeIntthe cellsize (m)
Returns:
true on success.
Example:
var g = new Grid(); // 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:
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
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_nameStringsource file name (relative to project folder)
Returns:
true on success.
load
-
fileName
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).
Parameters:
-
fileNameStringthe filename of the grid; paths are relatve to the root folder of the project.
Returns:
returns true on success
Example:
var g = new Grid(); // create a grid
g.load('gis/biggrid.asc'); // load the raster file
paint
-
min_value -
max_value
paint shows the content of the grid visually in iLand. Use min_value and max_value to provide a value range.
Parameters:
-
min_valueDoubleminimum value (mapped to bottom of the color ramp)
-
max_valueDoublemaximum value (mapped to top of the color ramp)
Example:
var g = Globals.grid('height'); // get height grid from iLand
g.paint(0,50);
registerUI
-
name
Registers the grid with the user interface of iLand (https://iland-model.org/iLand+viewer). The grid is added to the "Scripts" section of grids,
and iLand renders the grid when clicking on it. Default value range is set to min/max values within the grid. Note that a Grid's name is the
relative file path when loaded from disk.
Parameters:
-
nameStringName to use for the grid in the UI. When blank, the variable name is used.
Example:
// create a new grid and load some data var g = new Grid(Globals.path('gis/extra_grid.asc')); g.registerUI();
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_gridObjectGrid with target extent and resolution
save
-
file_name
Save to a file file_name as ESRI ASCII raster file.
See also: load
Parameters:
-
file_nameStringdestination 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.
Parameters:
-
xDoublenew value for the x-coordinate of the origin
-
yDoublenew value for the y-coordinate of the origin
Example:
var g = new Grid(); // 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:
-
xIntegerindex in x direction (between 0 and grid.width-1)
-
yIntegerindex in y direction (between 0 and grid.height-1)
-
valueDoublevalue 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 metric 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 and given in meters.
See also: value
Parameters:
-
xDoublemeters in x direction (between 0 and )
-
yDoublemeteres in y direction (between 0 and grid.height-1)
-
valueDoublevalue 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
Apply the expression expression on all pixels of the grid and return the sum of the values
See also: apply
Parameters:
-
expresionStringexpression to evaluate
Returns:
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 gridsumTrees
-
expresion -
filter
Evaluate the expression expression for all trees in the current treelist, and sum the
result of expression to the cells of the grid. With other words, the result is a grid
with a sum over expression for all trees on a cell. The filter lets you sum over a subset of trees.
See also: apply
Parameters:
-
expresionStringexpression to evaluate and sum for each grid cell
-
filterStringexpression to filter a subset of trees (empty is no filter)
Returns:
sum of expression over all cells
Example:
var g = Globals.grid('height'); // get a grid with the right size / resolution, here 10m
g.sumTrees('basalArea', 'species=piab'); //
g.save(Globals.path('temp/basal-area-spruce.asc'));value
-
x -
y
Access individual cell values with an index in x- and y-direction (i.e., values between 0 and the width/height-1). If the grid is empty, or the the given position is invalid, -1 is returned.
Note: For access with metric coordinates, use the valueAt() function!
See also: setValue
Parameters:
-
xIntegerindex in x direction (between 0 and grid.width-1)
-
yIntegerindex in y direction (between 0 and grid.height-1)
Returns:
value of the grid at position (x, y)
valueAt
-
x -
y
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.
Note: For access with index coordinates, use the value() function!
See also: setValue
Parameters:
-
xDoublecoordinate (m)
-
yDoublecoordinate (m)
Returns:
value of the grid at position (x, y)
values
()
Array
Get a Javascript array with that contains all the grid values as doubles.
See also: value
Returns:
Javascript array with all the values of the grid
Example:
var g = Globals.grid('height');
let hs = g.values(); // get a (large) array
// loop over the array
for (let i=0;i<hs.length;++i) {
// do something with hs[i] ....
}
// use JS mapping/filter functions
let bigs = hs.filter(h => h>50); // filter all grid values that are >50m
print("number of tall pixels: " + bigs.length);
Properties
isValid
Boolean
is true if the grid contains data.
minX
Double
minY
Double
name
String
gets or sets the name of the grid (that are used for calculations)