See examples of using the Code Block parameter. To do this, create a function definition in the Code Block parameter and reference the definition in the Expression parameter. These variables must be passed to the code block from the expression. You cannot access model variables in the Code Block parameter. To use a Python function in an expression, double-click a function in the Functions list to add it to the Expression parameter. To use a variable in the expression, enclose the variable name in percent signs (%) or double-click the variable name in the Variables list to add it to the Expression parameter. Variables created in ModelBuilder can be used by this tool, but they cannot be used directly in the Expression parameter. See examples of using the Expression parameter. The Code Block parameter cannot be used on its own it must be used in conjunction with the Expression parameter. Use the Code Block parameter for more complicated expressions, such as multiline calculations or logical operations (if, then). Use the Expression parameter for short one line expressions. Other scripting languages are not supported. The Expression parameter only supports Python expressions. The tool is not available from the Geoprocessing pane or from Python. In the dialog box in Input Layer select ndvi1000, configure the SRC, in Advanced Parameters > Output Data Type select Int32, execute.Ī raster called Converted is generated with values ranging from 0 to 874.This tool is only available from the ModelBuilder ribbon for use in models. Conversion > Translate (Convert Format), to convert the generated raster to integer.NDVI values are related to the presence or absence of vegetation, low values generally coincide with bare soils or water bodies.īy comparing the NDVI values with the satellite image, the following ranges are defined The reclassification of an NDVI can help the process of interpretation of a satellite image, it can also be useful to evaluate the result of a classification. Process Toolbox > Raster Analysis > Raster Layer Single Value ReportĢ.- Example in satellite images. Generating statistics: to quantify the area occupied by each range of slope select: To do this, enter the expression in the Raster 25) AND 50) AND 75) * 100Įxplanation: the * operator assigns a value to the pixels that meet the condition.Īs the generated raster has only 4 categories, it is possible to apply one style per Unique Value. The slope raster in percentage generated from the previous MOU presents values from 0 to 238, a reclassification is applied in ranges that allow a better interpretation of the relief: This procedure will facilitate the quantification of the surface of each class and the cartographic representation.įinally you can alter the text in the Labels and save the style. The tool runs and generates the output raster, which by default has the name Reclassified. In the menu Processes activate the Toolbox, then locate GRASS > r.reclass, in the dialog box the MDE is selected, in the text box Reclass Rules we place the expression that defines the intervals: QGIS 3 does not have a specific tool to reclassify for it we can use GRASS tools. To know the basic statistics of a Raster you must access to Layer Properties > Histogram or Layer Properties > Information, in the example the height values of the DEM range from 58 to 1635 masl. We can use reclassification in a DEM to generate a hypsometry map or in a slope raster to group by ranges. We call continuous raster those that represent a continuous variable in space such as elevation, precipitation, noise, among others, also includes satellite images or product generated. Examples in raster of continuous variables: These operations can be useful in the analysis of the different types of raster, Digital Elevation Models, discrete raster, satellite images. Reclassification allows you to group together the current values of a raster. Reassignment or reclassification operations consist of the total or partial modification of the values of a raster.
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