An overview of horizontal factor classes (arcpy.sa)
The horizontal factors (HFs) classes define the difficulty of moving from one cell to another while accounting for the horizontal elements that may affect the movement. The Path Distance tool uses the horizontal factor object to identify the horizontal factor. To determine the HF for moving from one cell to the next, the prevailing horizontal direction at the processing cell must be established from the horizontal direction raster. The horizontal relative moving angle (HRMA), the relationship between the moving direction with respect to the horizontal direction, is calculated and plotted on the horizontal factor graph to determine the horizontal factor. The resultant value establishes the horizontal factor from the center of the processing cell (the FROM cell) to the edge of the TO cell.
The same process is performed for the segment from the edge of the TO cell to its center. The prevailing horizontal direction at the TO cell is established, the HRMA determined, and a horizontal factor identified.
The larger the horizontal factor, the more difficult the movement. Negative values assigned to cell locations on the input horizontal factor raster indicate that no horizontal direction is specified for the cell. The HRMA cannot be defined for a cell containing no direction; therefore, the cell receives 1 as input for the HF in the Path Distance calculations.
To define the HRMA, the angle between the horizontal direction defined on the horizontal direction raster and the moving direction to the cell to which the cost distance is being calculated is determined. Even though the values range from -180 to +180, the HRMAs are symmetrical with respect to the horizontal factor axis; therefore, they are represented from 0 to 180 on the x-axis of the horizontal factor graph. The HRMA is the number of degrees the travel direction is from the specified horizontal direction, regardless of positive or negative orientation. Therefore, the range of HRMAs is 0 to 180 degrees.
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Defines the relationship between the horizontal cost factor and the horizontal relative moving angle through a binary function. If the horizontal relative moving angle is less than the cut angle, the horizontal factor is set to the value associated with the zero factor; otherwise it is infinity. |
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Defines the relationship between the horizontal cost factor and the horizontal relative moving angle through a forward function. The function establishes that only forward movement is allowed. |
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Defines the relationship between the horizontal cost factor and the horizontal relative moving angle through a linear function.The function specifies that the horizontal factor has a linear relationship with the horizontal relative moving angle. |
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Defines the relationship between the horizontal cost factor and the horizontal relative moving angle through an inverse linear function. The function specifies that the horizontal factor is an inverse linear function of the horizontal relative moving angle. |
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Defines the relationship between the horizontal cost factor and the horizontal relative moving angle through a specified table file. The table file identifies the horizontal factor graph used to determine the horizontal factors. |
Tools that use horizontal factor objects: