If it is undefined, meter will be used by default. You can use the Define Projection tool to specify a z-unit. It is recommended that you define a z-unit for the input raster if it is missing. If a z-unit is available in the vertical coordinate system of the input raster, it will be applied automatically. The Z unit parameter will be enabled only when the geodesic method is selected. This is because along the boundary of the input dataset, those cells do not have enough valid neighbors.Īspect is expressed in positive degrees from 0 to 360, measured clockwise from north.Ĭells in the input raster that are flat-with zero slope-are assigned an aspect of -1.įor the geodesic method, specifying the surface z-unit ensures the accuracy of the output. The cells in the outermost rows and columns of the output raster will be NoData. If there are fewer than seven valid cells, the calculation will not be performed, and the output at that processing cell will be NoData. Of the eight cells neighboring the processing cell, this tool requires that at least seven of them have a valid value. If the processing cell is NoData, the output for that location will be NoData. This tool uses a 3 by 3 cell moving window to process the data. You can continue to use the traditional approach of the Aspect tool if you need the results to exactly match previous tool runs or if fast execution time is more important than a better algorithm. This can be useful with gradual homogeneous terrain interrupted by streams, roads, or sharp breaks in slope. Surface Parameters also provides an adaptive window option that evaluates the local variability of the terrain and identifies the largest appropriate neighborhood size for each cell.
Larger window sizes are useful with high resolution elevation data to capture land surface processes at an appropriate scale. The Aspect tool uses a 3 by 3 window of cells to compute the value, while the Surface Parameters tool allows window sizes from 3 by 3 to 15 by 15 cells. The Surface Parameters tool fits a surface to the neighborhood of cells instead of a plane, which provides a more natural fit to the terrain. The Aspect tool fits a plane to the nine local cells, but a plane may not be a good descriptor of the landscape and may mask or exaggerate natural variations of interest. The Surface Parameters tool provides a newer implementation of aspect and is recommended to be used instead of the Aspect tool.
0 kommentar(er)
