Syntax

   @Hillshade([REJECTABLE], <azimuth>, <altitude>[, <interpolate nodata>[, <algorithm>]])

Arguments

   REJECTABLE

      Specifies if the function will supply a rejection code and message
      to the invalid feature and output it to the rejected port, or will
      fail upon being supplied invalid features.

      A feature can be rejected for the following reasons:
         - The feature has invalid geometry

   <azimuth>

      Azimuth angle of the light source, expressed in positive degrees from
      0 to 360, measured clockwise from north. The default value, 315, is
      the value typically used to generate shaded maps.

      Range: 0-360

   <altitude>

      Altitude angle of the light source above the horizon, expressed in
      positive degrees, with 0 degrees at the horizon and 90 degrees directly
      overhead.

      Range: 0-90

   <interpolate nodata>

      Whether to calculate values at raster edges and near nodata values.

      When this is set to 'DoNotInterpolateNodata', there will be a one pixel
      border around the edge of the raster set to the nodata value
      (i.e. the alpha band value will be set to 0).
      Additionally, when any pixel in the 3x3 window used to calculate the
      hillshade value is equal to nodata, the output pixel will also be
      set to nodata.

      When this is set to InterpolateNodata, values around the edge and near
      nodata values will be estimated by interpolating missing values.

      Range: InterpolateNodata | DoNotInterpolateNodata

   <algorithm>

      The algorithm used to calculate slope and aspect.

      Some analyses have suggested that Horn's formula is better suited to
      rougher terrain, whereas Zevenbergen & Thorne's formula is better for
      smooth terrain.

      Range: Horn | ZevenbergenThorne

Description

   The @Hillshade function is used to generate a shaded relief effect, useful
   for visualizing terrain.

   Each selected input band will be converted to a GRAY8 band with hillshade
   values between 0 and 255. Additionally, if <interpolate nodata> is disabled
   or if the band has a nodata value, an additional ALPHA8 band will be
   generated, with a value of 0 where the input was nodata and a value of 255
   where the input was data.

   Note that the horizontal and vertical units are expected to be equal.
   If this is not the case, @Scale may be used prior to this function to
   apply an appropriate scale factor.

   This function supports raster band selection. @SelectRaster can be used
   to modify selection.