QgsNineCellFilter class
Base class for raster analysis methods that work with a 3x3 cell filter and calculate the value of each cell based on the cell value and the eight neighbour cells.
Contents
Common examples are slope and aspect calculation in DEMs. Subclasses only implement the method that calculates the new value from the nine values. Everything else (reading file, writing file) is done by this subclass
Derived classes
- class QgsDerivativeFilter
- Adds the ability to calculate derivatives in x- and y-directions.
- class QgsRuggednessFilter
- Calculates the ruggedness index based on a 3x3 moving window.
- class QgsTotalCurvatureFilter
- Calculates total curvature as described by Wilson, Gallant (2000): terrain analysis.
Constructors, destructors, conversion operators
- QgsNineCellFilter(const QString& inputFile, const QString& outputFile, const QString& outputFormat)
- Constructor that takes input file, output file and output format (GDAL string)
Public functions
- auto processNineCellWindow(float* x11, float* x21, float* x31, float* x12, float* x22, float* x32, float* x13, float* x23, float* x33) -> float pure virtual
- Calculates output value from nine input values.
- auto processRaster(QgsFeedback* feedback = nullptr) -> int
- Starts the calculation, reads from mInputFile and stores the result in mOutputFile.
Protected variables
- float mInputNodataValue
- The nodata value of the input layer.
- float mOutputNodataValue
- The nodata value of the output layer.
- double mZFactor
- Scale factor for z-value if x-/y- units are different to z-units (111120 for degree->meters and 370400 for degree->feet)
Function documentation
float QgsNineCellFilter::
Calculates output value from nine input values.
| Parameters | |
|---|---|
| x11 | surrounding cell top left |
| x21 | surrounding cell central left |
| x31 | surrounding cell bottom left |
| x12 | surrounding cell top central |
| x22 | the central cell for which the value will be calculated |
| x32 | surrounding cell bottom central |
| x13 | surrounding cell top right |
| x23 | surrounding cell central right |
| x33 | surrounding cell bottom right |
| Returns | the calculated cell value for the central cell x22 |
The input values and the output value can be equal to the nodata value if not present or outside of the border. Must be implemented by subclasses.
First index of the input cell is the row, second index is the column
int QgsNineCellFilter::
Starts the calculation, reads from mInputFile and stores the result in mOutputFile.
| Parameters | |
|---|---|
| feedback | feedback object that receives update and that is checked for cancelation. |
| Returns | 0 in case of success |