what are local operations,max in single iteration , max in double iteration?
Answers
Answer:
As you’ve learned, map algebra uses math-like operations. For example, you can apply simple math like addition or multiplication to update raster cell values.
The most common type of map algebra is a cell-by-cell function. This type has rasters directly stacked on top of one another. Then, the function applies for cells aligned to each other.
But you can also change the configuration so it’s not only cell-by-cell. Here are the types of map algebra operations that you can use:
Local
Focal
Zonal
Global
The simplest approach is map algebra on a cell-by-cell basis. For example, you have 2 rasters stacked on top of each other. Then, you add each cell one-by-one.
If raster cells represent temperature, you can subtract them both at different time periods. By using a local operation, you can find the difference in temperature for each cell.
Global operations apply a bulk change to all cells in a raster. If you want to add a value of 1 to all grid cells, this is a global operation.
For example, Euclidean distance is an example of a global operation. By calculating the closest distance away from a source, it applies the function globally in a raster.
Focal operations are spatial functions that compute an output value of each cell using neighborhood values. For example, convolution, kernel and moving windows are focal operations.
MOVING WINDOW: A moving window is a rectangular arrangement of cells that shifts in position. By applying an operation to each cell from a moving window, it commonly smooths values in a raster.
Mathematical Functions
Here are examples of operations that you can use for map algebra:
Arithmetic operations (addition, subtraction, multiplication, division)
Statistical operations (minimum, maximum, average, median)
Relational operations (greater than, smaller than, equal to)
Trigonometric operations (sine, cosine, tangent, arcsine)
Exponential and logarithmic operations (exponent, logarithm)