Slope function
Slope represents the rate of change of elevation for each digital elevation model (DEM) cell. It's the first derivative of a DEM.
The inputs for this function are the following:
- Input DEM
- Output Measurement
- Z Factor
- Pixel Size Power
- Pixel Size Factor
By default, the slope appears as a grayscale image. You can add the Colormap function to specify a particular color scheme, or allow the person viewing the mosaic to modify the symbology with their own color scheme.
This Slope function uses an accelerated atan() function. It is six times faster, and the approximation error is always less than 0.3 degrees.
Output Measurement
The inclination of slope can be output as either a value in degrees (using one of two options) or percent rise. There are three options:
DEGREE—The inclination of slope is calculated in degrees. The values range from 0 to 90.
SCALED—The inclination of slope is calculated the same as DEGREE, but the z-factor is adjusted for scale. It uses the Pixel Size Power and Pixel Size Factor values, which account for the resolution changes (scale) as the viewer zooms in and out. This is recommended when using worldwide datasets projected using World Mercator—particularly when using slope as a surface for visualization.
The z-factor is adjusted using the following equation:
Adjusted Z Factor = (Z Factor) + (Pixel Size)Pixel Size Power × (Pixel Size Factor)
PERCENT_RISE—The inclination of slope is output as percentage values. The values range from 0 to essentially infinity. A flat surface is 0 percent and a 45-degree surface is 100 percent, and as the surface becomes more vertical, the percent rise becomes increasingly larger.
Z Factor
The z-factor is a scaling factor used to convert the elevation values for two purposes:
- To convert the elevation units (such as meters or feet) to the horizontal coordinate units of the dataset, which may be feet, meters, or degrees.
- To add vertical exaggeration for visual effect.
Units conversion
If the units of measure for the z (elevation) units are the same as the x,y (horizontal) units, then the z-factor is 1. If the units of measure are different, then you will need to define a z-factor to account for the difference.
To convert from feet to meters or vice versa, see the table below. For example, if your DEM's elevation units are feet and your mosaic dataset's units are meters, you would use a value of 0.3048 to convert your elevation units from feet to meters (1 foot = 0.3048 meters).
This is also useful when you have geographic data (such as DTED in GCS_WGS 84 using latitude and longitude coordinates) where the elevation units are in meters. In this case, you need to convert from meters to degrees (0.00001; see below). The value for degree conversions are approximations.
From | To | ||
|---|---|---|---|
Feet | Meters | Degrees | |
Feet | 1 | 0.3048 | 0.000003 |
Meters | 3.28084 | 1 | 0.00001 |
Vertical exaggeration
To apply vertical exaggeration, you must multiply the conversion factor by the exaggeration factor. For example, if both elevation and dataset coordinates are meters and you want to exaggerate by a multiple of 10, the scaling factor would be unit conversion factor (1.0 from the table) multiplied by the vertical exaggeration factor (10.0), or 10. As another example, if the elevations are meters and the dataset is geographic (degrees), you would multiply the units conversion factor (0.00001) by 10 to get 0.0001.