Hillshade function
A hillshade is a grayscale 3D representation of the surface, with the sun's relative position taken into account for shading the image. This function uses the altitude and azimuth properties to specify the sun's position.
The inputs for this function are the following:
- Input DEM
- Azimuth
- Altitude
- Scaling
- Z Factor
- Pixel Size Power
- Pixel Size Factor
- Remove Edge Effect
By default, a grayscale color ramp is used to display a hillshaded elevation model. The following image displays an elevation model using the default hillshade symbology.
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Example hillshaded image. |
Azimuth and altitude
The properties altitude and azimuth together indicate the sun's relative position that will be used for creating any 3D model (hillshade or shaded relief). Altitude is the sun's angle of elevation above the horizon and ranges from 0 to 90 degrees. A value of 0 degrees indicates that the sun is on the horizon, that is, on the same horizontal plane as the frame of reference. A value of 90 degrees indicates that the sun is directly overhead.
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Azimuth is the sun's relative position along the horizon (in degrees). This position is indicated by the angle of the sun measured clockwise from due north. An azimuth of 0 degrees indicates north, east is 90 degrees, south is 180 degrees, and west is 270 degrees.
Scaling, Pixel Size Power, and Pixel Size Factor
The hillshade result is scaled dynamically by adjusting the z factor using one of two options:
- None—This applies a linear adjustment by modifying the z factor according to the cell size, thereby accounting for altitude changes (scale) as the viewer zooms in and out. This is ideal for single raster datasets covering a local area. This is not recommended for world-wide datasets as it will produce a fairly flat (gray) image when zoomed out.
- Adjusted—This applies a nonlinear adjustment using the default Pixel Size Power and Pixel Size Factor values, which account for the altitude changes (scale) as the viewer zooms in and out. These values are recommended when using world-wide datasets projected using World Mercator.
The z factor is adjusted using the following equation:
Adjusted Z Factor = (Z Factor) + (Pixel Size)Pixel Size Power × (Pixel Size Factor)
Z factor
The z factor is 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. The value for degree conversions are approximations, and depend on the latitude of your area of interest.
From | To | ||
|---|---|---|---|
Feet | Meters | ||
Feet | 1 | 0.3048 | |
Meters | 3.28084 | 1 | |
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.
Remove Edge Effect
Using this option will avoid any resampling artifacts that may occur along the edges of a raster. The output pixels along the edge of a raster or beside pixels without a value will be populated with NoData; therefore, it is recommended that this option be used only when there are other rasters with overlapping pixels available. When overlapping pixels are available, these areas of NoData will display the overlapping pixel values, instead of being blank.
Using this option will remove any resampling artifacts that may occur along the edges of a raster. The output pixels along the edge of a raster or adjacent to a pixel of NoData will be populated with NoData; therefore, it is recommended that this option be used only when there are other rasters with overlapping pixels available so that the areas of NoData will display the overlapping pixels, instead of being blank.
- Unchecked—Bilinear resampling will be applied uniformly to resample your hillshade. This is the default.
- Checked—Bilinear resampling will be used within the hillshade, except along the edges of the rasters or beside pixels of NoData. These pixels will be populated with NoData, since it will reduce any sharp edge effects that may occur.