This raster analysis portal tool is available when you are signed in to an ArcGIS Enterprise portal that has ArcGIS Image Server configured for Raster Analysis. When the tool is run, ArcGIS Pro serves as a client and the processing occurs in the servers federated with ArcGIS Enterprise. The portal tool accepts layers from your portal as input and creates output in your portal.
The input raster layer supports a layer from the portal, a URI or URL to an image service, or the output from the Make Image Server Layer tool. The input feature layer can be a layer from the portal or a URI or URL to a feature service. This tool does not support local raster data or layers. While you can use local feature data and layers as input to this portal tool, best practice is to use layers from your portal as input.
When the Slope option is specified for Parameter Type, the output represents the rate of change of elevation for each digital elevation model (DEM) cell. It is the first derivative of a DEM. The range of values from the slope output depends on the type of measurement units.
When the Aspect option is specified for Parameter Type, the output identifies the compass direction that the downhill slope faces for each location. It is expressed in positive degrees from 0 to 360, measured clockwise from north.
Curvature is used to describe the shape of a surface. When applied to earth science, it is used to help explain the impacts of gravity, erosion, and other factors on the surface and is used in conjunction with other surface parameters to identify and classify landforms. The curvature options for Parameter Type are described as follows:
- Mean curvature—The overall curvature of the surface. It is computed as the average of the minimum and maximum curvature. When this option is specified, the output is equivalent to the mean of profile (normal slope line) and tangential (normal contour) curvatures. Its sign, positive or negative, is not a definitive indicator except at extreme values. High positive values indicate areas of maximum denudation, and high negative values indicate areas of maximum accumulation (Minár et al., 2020).
- Tangential (normal contour) curvature—The geometric normal curvature perpendicular to the slope line, tangent to the contour line. Positive values indicate areas of diverging surface flow. Negative tangential curvatures indicate areas of converging surface flow. A positive tangential (normal contour) curvature indicates that the surface is convex at that cell perpendicular to the direction of the slope. A negative curvature indicates that the surface is concave at that cell in the direction perpendicular to the slope. A value of 0 indicates that the surface is flat.
- Profile (normal slope line) curvature—The geometric normal curvature along the slope line. Positive values indicate areas of acceleration of surface flow and erosion. Negative profile curvature indicates areas of slowing surface flow and deposition. A positive profile (normal slope line) curvature indicates that the surface is convex at that cell in the direction of the slope. A negative curvature indicates that the surface is concave at that cell in that same direction. A value of 0 indicates that the surface is flat.
- Plan (projected contour) curvature—The curvature along contour lines.
- Contour geodesic torsion—The rate of change in slope angle along contour lines.
- Gaussian curvature—The general curvature of a surface. It is computed as the product of the minimum and maximum curvature and can take negative and positive values. Positive values indicate that
the surface is convex at that cell, and negative values indicate
that it is concave. A value of 0 indicates that the surface is
flat.
- Casorati curvature—The general curvature of the surface. It can be zero or always positive. High positive values indicate areas of sharp bending in multiple directions.
The units of all curvature type outputs will be the reciprocal (the square of the reciprocal for Gaussian curvature) of the x,y-units of the Output Coordinate System environment setting.
The Quadratic option of the Local Surface Type parameter does not fit the neighborhood cells exactly. This is the default and recommended option for most data and applications.
- The quadratic surface minimizes the effect of noisy surface data such as a high-resolution lidar surface, which is especially important when computing curvature.
- Use the quadratic surface when specifying a neighborhood size that is larger than the cell size and when using the adaptive neighborhood option.
The Biquadratic option of the Local Surface Type parameter fits the data from the neighborhood cells exactly.
- This option is suitable for a highly accurate input surface.
- If the neighborhood distance is larger than the input raster cell size, the accuracy advantages of the biquadratic surface type will be lost. Leave the neighborhood distance as the default (equal to the cell size).
The Neighborhood Distance parameter determines the neighborhood size and calculates the surface parameter over this distance from the target cell center.
- It cannot be less than the input raster cell size.
- A smaller neighborhood distance captures more local variability in the landscape such as characteristics of smaller landscape features. With high resolution elevation data, larger distances may be more appropriate.
When the Use Adaptive Neighborhood parameter is checked (useAdaptiveNeighborhood = "ADAPTIVE_NEIGHBORHOOD" in Python), the neighborhood distance will change with variability in the terrain. The neighborhood distance will lessen if there is too much variability in the calculation window.
Specifying the surface Z Unit parameter value ensures the proper computation of the slope output.
If a z-unit is available in the vertical coordinate system of the input raster, it will be applied automatically. It is recommended that you define a z-unit for the input raster if it is missing. You can use the Define Projection tool to specify a z-unit. If it is undefined, meter will be used by default.
The range of values in the slope output depends on the Output Slope Measurement parameter value:
- Degrees—The range of slope values is 0 to 90.
- Percent rise—The range is 0 to essentially infinity. A flat surface is 0 percent, a 45 degree surface is 100 percent, and as the surface becomes more vertical, the percent rise becomes increasingly larger.
If the Project Geodesic Azimuths parameter is checked (projectGeodesicAzimuths = "PROJECT_GEODESIC_AZIMUTHS" in Python), the following are true:
- North is always represented by 360 degrees.
- Azimuths will be projected to correct the distortion caused by a nonconformal Output Coordinate System environment system value. These angles can be used to accurately locate points along the steepest downhill slope.
If the Use Equatorial Aspect parameter is checked (useEquatorialAspect = "EQUATORIAL_ASPECT" in Python), aspect will be measured from a point along the equator to correct the skewing of direction that occurs when approaching the poles. This parameter ensures that the north-south and east-west axes are perpendicular to each other.
Check the Use Equatorial Aspect parameter if the terrain is near the north or south pole.
Use the Input Analysis Mask parameter to limit the analysis to specific locations of interest within the Input Surface Raster. The locations can be defined by a raster or feature data. The Input Analysis Mask parameter will take priority over the Mask environment setting.
When the Input Surface Raster and Input Analysis Mask parameter values are of the same cell size and the cells are aligned, they will be used directly in the tool. They will not be resampled internally during tool operation.
If the cell size is different, the output cell size will be the maximum of the inputs, and the Input Surface Raster value will be used internally as the snap raster. If the cell size is the same but the cells are not aligned, the Input Surface Raster value will be used internally as the snap raster. Either of these cases will cause an internal resampling before the extraction operation is performed.
For additional information, see the Cell Size and Snap Raster environment topics.