“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 of raster data is made up of cells it allows us to do arithmetic computations on the cells and generate new data. The most common raster operation is raster recode which allows us to generate a simplified raster layer ie converting a raster to a binary one.
In this module, we will look at how rasters can be manipulated by using arithmetic operations. 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.
Produce a reclassified raster with 2 classes.
Advanced users Explore the possibility of creating 3 or more classes using the raster calculator.
Reclassify the original raster to 3 classes with the following pixel ranges. Modify the Recode* expression to suit your needs.
|Pixel Range||New Value|
|Pixel_value < 200||0|
|Pixel_value > 200 and < 1000||1|
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.
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.