Added pixel type attribute to the output image of program shadow. Fixes #5187 (#659)

<application name="shadow" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="http://isis.astrogeology.usgs.gov/Schemas/Application/application.xsd">

  <brief>

    High accuracy hillshade with shadow casting

    Create a high accuracy hillshade with shadow casting

  </brief>

  <description>

    This program will create a shaded-relief cube from a DEM and match cube.<br/><br/>

    This program, shadow, will create a shaded-relief cube from a digital

    elevation model (DEM) and a MATCH cube.<br/><br/>

    This program operates much like 'shade' but instead of an azimuth/elevation input, we use the

      sun's position at the center of the given cube or at a given time and, by default, factor in

      shadows cast by features.<br/><br/>

    We use the sun's position at the center of the input cube or a user-defined

    observation time. By default, we factor in shadows cast by features.

    This program operates much like the ISIS3 'shade' program which instead requires azimuth/elevation as input.<br/><br/>

    Using the sun's position allows much higher precision shading and enables the possibility of

    computing shadowed areas. The algorithm description below is provided to help understand the

    However, with the shadow application, using the sun's position allows much

    higher precision shading and enables the possibility of computing shadowed areas.

    The algorithm description below is provided to help understand the

    optimization settings.<br/><br/>

    <strong>User-Requirements</strong><br/>

      The user must supply an elevation model (DEM) and either an observation time or a cube

      with raw camera geometry (see spiceinit).<br/><br/>

      with raw camera geometry (see 'spiceinit').<br/><br/>

    <strong>Understanding the Algorithm</strong><br/>

    The shade program's algorithm is called 'hillshade' in this algorithm description.

    The 'shade' program's algorithm is called 'hillshade' in this algorithm description.

    <ol>

      <li>

      </li>

      <li>

        For every pixel in the input elevation model<br/>

        For every pixel in the input elevation model, compute the hillshade value for the pixel, and<br/>

      </li>

      <ol>

        <li>

          Compute the hillshade value for the pixel, and

        </li>

        <li>

          if the hillshade result is positive (facing towards the sun) then estimate if the pixel is

          if the hillshade result is positive (facing towards the sun), then estimate if the pixel is

          in shadow;

        </li>

        <li>

          if the hillshade value is positive and the pixel is in shadow then the result is an LRS;

          if the hillshade value is positive and the pixel is in shadow, then the result is an LRS;

        </li>

        <li>

          if the hillshade value is positive and the pixel is not in shadow then the result is the

          if the hillshade value is positive and the pixel is not in shadow, then the result is the

          hillshade result and

        </li>

        <li>

          if the hillshade value is negative the result is an LRS

          if the hillshade value is negative, the result is low resolution saturation (LRS).

        </li>

      </ol>

    </ol>

    The algorithm to estimate if a pixel is in shadow

    The algorithm to estimate if a pixel is in shadow:

    <ol>

      <li>

        <b>Optimization: If SHADOW, and this elevation model pixel is known to be shadowed,

        Optimization: If SHADOW, and this elevation model pixel is known to be shadowed,

          consider this pixel to be shadowed and stop (no pixels are initially known to be

          shadowed)</b>.

          shadowed).

      </li>

      <li>

        Compute the pixel's body-fixed coordinate (XYZ) position.

          the sun.

      </li>

      <li>

        Subtract the sun's position from the elevation model pixel's position, giving you a vector

        Subtract the sun's position from the elevation model pixel's position, providing a vector

        to the center (or edge) of the sun.

      </li>

      <li>

        <li>

          Update estimate of how far along the 3D ray is equivalent to the full resolution of the

          elevation model.<br/>

          <b>Optimization: Multiply the step by PRECISION</b>.<br/>

          <b>Optimization : If SKIPOVERSHADOW, while the next linearly-extrapolated elevation

          Optimization: Multiply the step by PRECISION.<br/>

          Optimization : If SKIPOVERSHADOW, while the next linearly-extrapolated elevation

          model position is known to be in shadow, increase the next step size by the

          estimate up to MAXSKIPOVERSHADOWSTEPS times</b>.

          estimate up to MAXSKIPOVERSHADOWSTEPS times.

        </li>

        <li>Check for a solution</li>

        <ul>

          <li>

            If the ray's elevation is higher than the highest point on the elevation model,

            the originating pixel is in light.<br/>

            <b>Optimization: If LIGHTCURTAIN, and the ray's elevation is higher than a previous ray

            Optimization: If LIGHTCURTAIN, and the ray's elevation is higher than a previous ray

              that intersected this pixel in the elevation model, consider the

              originating pixel in light</b>.

              originating pixel in light.

          </li>

        </ul>

        <li>

            <li>

              If LIGHTCURTAIN, and the pixel was determined to be in light, record the elevations of

              the ray where it projected onto the elevation model.<br/>

              <b>Optimization: If LOWERLIGHTCURTAIN, lower the elevations along the ray by

              Optimization: If LOWERLIGHTCURTAIN, lower the elevations along the ray by

                 subtracting the minimum difference between the ray and the elevation model while

                 the ray was being walked.</b>.<br/>

              <b>Optimization: If CACHEINTERPOLATEDVALUES, linearly interpolate the points where the

                 ray would have intersected the elevation model to one pixel accuracy</b>.

                 the ray was being walked.<br/>

              Optimization: If CACHEINTERPOLATEDVALUES, linearly interpolate the points where the

                 ray would have intersected the elevation model to one pixel accuracy.

            </li>

            <li>

              If SHADOWMAP, and the pixel was determined to be in shadow, record all points where

              the ray projected onto the elevation model to be known shadowed points, excluding

              the actual intersection point.<br/>

              <b>Optimization: If CACHEINTERPOLATEDVALUES, linearly interpolate the points where the

                 ray would have intersected the elevation model to one pixel accuracy</b>.

              Optimization: If CACHEINTERPOLATEDVALUES, linearly interpolate the points where the

                 ray would have intersected the elevation model to one pixel accuracy.

            </li>

          </ul>

        </li>

    cache, and 16 bytes for the shadow cache, but the caches are hash-based causing a large amount

    of potential overhead. The caches are not limited to their specified sizes, only reduced

    to them periodically, and larger cache sizes result in this program consuming more memory.

    Although the larger the cache, the longer takes to lookup a single value (which happens often),

    in general larger caches mean less CPU time for the cost of memory.

    The larger the cache, the longer it takes to lookup a single value (which happens often).

    In general, larger caches mean less CPU time for the cost of memory.

  </description>

  <category>

    <change name="Kristin Berry" date="2015-07-22">

     Added NaifStatus::CheckErrors() to see if any NAIF errors were signaled. References #2248.

    </change>

    <change name="Kaitlyn Lee" date="2018-02-17">

     Added the PixelType attribute to the output cube and set it to real.

     Documentation updated by editor. Fixes #5187.

    </change>

  </history>

  <groups>

      </parameter>

      <parameter name="TO">

        <type>cube</type>

        <pixelType>real</pixelType>

        <fileMode>output</fileMode>

        <brief>

          Shaded and shadowed DEM

        <description>

          This is the estimated radius of the sun in solar radii. Since the unit "solar radius" is

          not our best guess of the sun's radius, the default is slightly different than 1.

          A larger number has the end effect of lessening shadows, a smaller number increases

          shadows. The sun's radius is only used for shadow computations, hillshade always uses the

          A larger number has the end effect of lessening shadows; a smaller number increases

          shadows. The sun's radius is only used for shadow computations. Hillshade always uses the

          sun's center.

        </description>

        <minimum inclusive="no">0.0</minimum>

        </brief>

        <description>

          This should be the time of the observer to use for the sun's position. The entered time

          will be adjusted for light-time between the sun and the observer. The format should be:

          "YYYY-MM-DDTHH:MM:SS.SSS" - for example: "2012-01-01T14:25:15.36"

          will be adjusted for light-time between the sun and the observer. The format should be

          "YYYY-MM-DDTHH:MM:SS.SSS"; for example, "2012-01-01T14:25:15.36"

        </description>

      </parameter>

    </group>

        <description>

          This is a list of quick settings for the other parameters in the Optimizations group. This

          also includes the ability to disable the shadow computations entirely. These options are

          provided for those who don't need a lot of customization or don't want to calculate

          provided for those who do not need a lot of customization or do not want to calculate

          shadow positions.

        </description>

        <list>

        </brief>

        <description>

          When a ray is determined to be in shadow, every DEM pixel between the original position and

          the point at which the DEM intersected the ray will be marked as in shadow. We then don't

          have to do any significant work when processing a pixel we previously determined was in

          the point at which the DEM intersected the ray will be marked as in shadow. We then perform no

          significant work when processing a pixel that we previously determined was in

          shadow. This also helps avoid unnecessary ray-DEM intersection checks (because surfaces

          aren't shadowed by surfaces already in shadow).

          are not shadowed by surfaces already in shadow).

        </description>

        <inclusions>

          <item>BASESHADOWCACHESIZE</item>

        </brief>

        <description>

          The shadow cache is allowed to grow to an unlimited size while the shadowing algorithm is

          processing. However, periodically the caches are shrunk - this is the approximate number

          of elements to shrink the shadow cache to. The shrinking is optimized in a way that

          processing. This is the approximate number of elements to shrink the

          shadow cache to, as periodically the caches are shrunk. The shrinking is optimized in a way that

          is mostly respected, but not guaranteed.

        </description>

        <minimum inclusive="yes">0</minimum>

        </brief>

        <description>

          The light curtain cache is allowed to grow to an unlimited size while the shadowing

          algorithm is processing. However, periodically the caches are shrunk - this is the

          approximate number of elements to shrink the light caches to. The shrinking is optimized

          algorithm is processing. This is the approximate number of elements to

          shrink the light caches to, as periodically the caches are shrunk. The shrinking is optimized

          in a way that this is mostly respected, but not guaranteed.

        </description>

        <minimum inclusive="yes">0</minimum>

        </brief>

        <description>

          This is a means to lessen the number of ray-DEM intersection checks by guessing the

          next ray-DEM intersection location and checking if it's in shadow. If it is, the ray

          next ray-DEM intersection location and checking if it is in shadow. If it is, the ray

          is stepped farther before the next intersection test (up to MAXSKIPOVERSHADOWSTEPS

          farther).

        </description>

          Distance to consider SKIPOVERSHADOW valid

        </brief>

        <description>

          Since the ray won't make a perfectly straight line across the DEM (DEMs are

          Since the ray will not make a perfectly straight line across the DEM (DEMs are

          projected onto a flat surface) a linear guess as to the next intersection point degrades

          in accuracy (depending on a number of factors, such as ray elevation, projection type, and

          DEM accuracy). This controls how far the algorithm can guess the next intersection point

      <description>

        This example will cover running this program in balanced mode.

        The input file "localdem.cub" was produced with the commands:

        The input file "localdem.cub" was produced with the following commands:

        <pre>

          spiceinit from=ab102401.cub

          fx from=ab102401.cub to=ab102401.radii.cub equation="radius(f1)"

      <guiInterfaces>

        <guiInterface>

          <image width="520" height="550" src="assets/images/example1_gui.jpg">

            <brief>Example's parameters in the graphical interface</brief>

            <brief>Example of parameters in the graphical interface</brief>

            <description>

              Run this program given a high resolution DEM 'localdem.cub' and the lighting

              characteristics from 'ab102401.cub' to create 'shadowed.cub'

              Run this program using the high resolution DEM 'localdem.cub' and the lighting

              characteristics from 'ab102401.cub' to create the 'shadowed.cub'

            </description>

            <thumbnail width="189" height="200" caption="Graphical Interface"

                src="assets/thumbs/example1_gui.jpg"/>

        <image width="373" height="550" src="assets/images/example1_from.jpg">

          <brief>FROM DEM to do shaded relief and shadow calculations on</brief>

          <description>

            This is the elevation model for which we're computing a shaded relief and shadow

            positions for. This is the FROM cube.

            This is the elevation model for which the shaded relief and shadow

            positions are to be computed. This is the FROM cube.

          </description>

          <thumbnail width="136" height="200" caption="FROM DEM"

              src="assets/thumbs/example1_from.jpg"/>

        <image width="458" height="550" src="assets/images/example1_match.jpg">

          <brief>MATCH image for computing the sun position</brief>

          <description>

            This is the image we're gathering the sun position from. In other words, we're trying

            We gather the sun position from this image. In other words, we are trying

            to make the DEM look like this image.

          </description>

          <thumbnail width="167" height="200" caption="MATCH cube"

          <brief>Output shaded relief with shadows</brief>

          <description>

            This is the result of the shadow program. This is the TO cube.

            The shadows are not as big as the shadows we see in the projected MATCH image because

            we're computing the fully shadowed areas in this program. Areas of the image that are

            getting less light, but aren't fully shadowed, look like they are in shadow but still

            have detail in them. To extend the shadow computations to encompass the visible

            we have computed the fully shadowed areas in this program. Areas of the image that are

            getting less light, but not fully shadowed, still appear in the shadow, but

            show more detail in them. To extend the shadow computations to encompass the visible

            shadow completely you can turn off SUNEDGE.

          </description>

          <thumbnail width="136" height="200" caption="Output Shadowed Shaded Relief"

          <image width="425" height="550" src="assets/images/example2_gui.jpg">

            <brief>Example's parameters in the graphical interface</brief>

            <description>

              Run this program given a the DEM 'dem.cub' and the lighting

              characteristics from midnight March 1st, 2012 to create 'shadowed_dem.cub'

              Run this program given the DEM 'dem.cub' and the lighting

              characteristics from midnight March 1st, 2012 to create 'shadowed_dem.cub'.

            </description>

            <thumbnail width="154" height="200" caption="Graphical Interface"

                src="assets/thumbs/example2_gui.jpg"/>

        <image width="550" height="276" src="assets/images/example2_from.jpg">

          <brief>FROM DEM to do shaded relief and shadow calculations on</brief>

          <description>

            This is the elevation model for which we're computing a shaded relief and shadow

            positions for. This is the FROM cube.

            This is the elevation model for which the shaded relief and shadow

            positions are to be computed. This is the FROM cube.

          </description>

          <thumbnail width="200" height="100" caption="FROM DEM"

              src="assets/thumbs/example2_from.jpg"/>

          <description>

            This is the result of the shadow program. This is the TO cube.

            This is what a mosaic of the entire moon would look like, approximately, if all of the

            This is what a mosaic of the entire moon would look like, approximately, if all

            images were taken at one time.

          </description>

          <thumbnail width="200" height="100" caption="Output Shadowed Shaded Relief"