“Raster consists of pixels which are organised in rows and columns. Each pixel has got a values which represents a specific phenomenon on the earth surface. Because raster are based on pixel we can do ”
In this module, we will look at how raster can be manipulated by using arithmetic operation. Raster data is very useful as it gives us information over a large scale and we can then derive new datasets from these. Let's dig in and explore the raster calculator.
Goal: To learn how to reclassify raster pixel values into 2 or 3 categories with raster calculator.
Check your results:
Produce a reclassified raster with 2 or 3 classes and total area of each class.
To Do: Calculate the area of each class
Name | Expectation |
---|---|
Raster Layer |
srtm_41_19 |
Operation |
Arithmetic |
Expressions |
("[email protected]" < 200) * 1 |
Raster style |
Single band pseudocolour, Equal interval and two classes |
Area |
$Area |
Raster analysis enforces its spatial relationships based on the location of the cell. Raster operations performed on multiple input raster datasets generally output cell
values that are the result of computations on a cell-by-cell basis. The value of the output for one cell is usually independent of the value or location of other input or output cells. In some cases, output cell values are influenced by neighbouring cells or groups of cells, such as in focal functions. There are mainly three types of raster analysis operations namely local, focal and zonal.
Raster calculator provides a means to do cell by cell analysis by using arithmetic operations and mathematical formulae to compute new outputs. Raster calculator functions mainly fall into the local operations category. These constitute the bulk of the analysis techniques that occur for rasters. The cell values of the new raster are computed by a function relating the input to output or are assigned by a classification table.
Click here to download the sample data for the lesson.