BurnMatrix

Creation

A BurnMatrix belongs to an Extent. It is a mathematical abstraction representing all the pixels in an extent. A BurnExtent is a MathJS SparseMatrix whose size is the same as the size of the Extent. For example, an Extent that is 3 tiles wide by 2 tiles tall, with a tilesize of 256 pixels, will have a BurnMatrix of size [256 * 3, 256 * 2].

A BurnMatrix is created and associated with an extent when a new Extent is created. The Extent is also available from the BurnMatrix - there is always a 1 to 1 relationship, meaning Extents won't share a BurnMatrix, and vice versa.

A BurnMatrix is dynamic, meaning its state is constantly changing over the life of the algorithm. Looking at a BurnMatrix at one point in time tells you nothing about its state at another point in time. However, a snapshot of the BurnMatrix is taken at every Timestep, so the evolution of the BurnMatrix can be seen by following the trail of its snapshots through an array of Timesteps.

Coordinates

A Mathjs matrix is a wrapped around a javascript array. A 2 dimensional matrix is an array of inner arrays:

const matrix = math.zeros(2, 3)

[
    [0, 0, 0],
    [0, 0, 0]
];

Note that the coordinates for all matrix operations are in [y, x] format. A BurnMatrix redefines any necessary matrix methods to use [x, y] coordinates for consistency with canvas data methods. For example, CanvasRenderingContext2D.getImageData() takes coordinates in [x, y] order. For this reason, it is better not to access the underlying MathJS matrix directly, but rather use the BurnMatrix.get and BurnMatrix.set methods, using [x,y] coordinates.