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<meta property="og:title" content="Trigonometric  transformation of a slope and aspect interaction — sa.trans" />
<meta property="og:description" content="The Trigonometric  Stage (1978) 
             [slope * cos(aspect)] or [slope * sin(aspect)]
An a priori assumption of a maximum in the NW quadrant (45 azimuth)
and a minimum in the SW quadrant can be replaced by an empirically
determined location of the optimum without repeated calculations of
the regression fit. In addition it is argued that expressions for
the effects of aspect should always be considered as terms involving
an interaction with slope (Stage, 1976)
For slopes from 0
bounded from -1 to 1. Greater than 100
out of the -1 to 1 range.
An alternative for slopes with values approaching infinity is
to take the square root of slope/100 to reduce the range of
values.By default this model test all values greater than 100
to 101" />




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    <h1>Trigonometric  transformation of a slope and aspect interaction</h1>
    <small class="dont-index">Source: <a href='https://github.com/jeffreyevans/spatialEco/blob/master/R/sa.trans.R'><code>R/sa.trans.R</code></a></small>
    <div class="hidden name"><code>sa.trans.Rd</code></div>
    </div>

    <div class="ref-description">
    <p>The Trigonometric  Stage (1978) 
             [slope * cos(aspect)] or [slope * sin(aspect)]</p>
<p>An a priori assumption of a maximum in the NW quadrant (45 azimuth)
and a minimum in the SW quadrant can be replaced by an empirically
determined location of the optimum without repeated calculations of
the regression fit. In addition it is argued that expressions for
the effects of aspect should always be considered as terms involving
an interaction with slope (Stage, 1976)</p>
<p>For slopes from 0<!-- % - 100%, The functions are linearized and -->
bounded from -1 to 1. Greater than 100<!-- % slopes are treated -->
out of the -1 to 1 range.</p>
<p>An alternative for slopes with values approaching infinity is
to take the square root of slope/100 to reduce the range of
values.By default this model test all values greater than 100<!-- % -->
to 101<!-- % and flat areas (-1) to nodata. --></p>
    </div>

    <pre class="usage"><span class='fu'>sa.trans</span><span class='op'>(</span>
  <span class='va'>slope</span>,
  <span class='va'>aspect</span>,
  type <span class='op'>=</span> <span class='st'>"cos"</span>,
  slp.units <span class='op'>=</span> <span class='st'>"degrees"</span>,
  asp.units <span class='op'>=</span> <span class='st'>"degrees"</span>
<span class='op'>)</span></pre>

    <h2 class="hasAnchor" id="arguments"><a class="anchor" href="#arguments"></a>Arguments</h2>
    <table class="ref-arguments">
    <colgroup><col class="name" /><col class="desc" /></colgroup>
    <tr>
      <th>slope</th>
      <td><p>slope values in degrees, radians or percent</p></td>
    </tr>
    <tr>
      <th>aspect</th>
      <td><p>aspect values in degrees or radians</p></td>
    </tr>
    <tr>
      <th>type</th>
      <td><p>Type of transformation, options are: "cos", "sin"</p></td>
    </tr>
    <tr>
      <th>slp.units</th>
      <td><p>Units of slope values, options are: "degrees", 
"radians" or "percent"</p></td>
    </tr>
    <tr>
      <th>asp.units</th>
      <td><p>Units of aspect values, options are: 
"degrees" or "radians"</p></td>
    </tr>
    </table>

    <h2 class="hasAnchor" id="value"><a class="anchor" href="#value"></a>Value</h2>

    <p>A vector of the modeled value</p>
    <h2 class="hasAnchor" id="references"><a class="anchor" href="#references"></a>References</h2>

    <p>Stage, A. R. 1976. An Expression of the Effects of Aspect, Slope, 
  and Habitat Type on Tree Growth. Forest Science 22(3):457-460.</p>
    <h2 class="hasAnchor" id="author"><a class="anchor" href="#author"></a>Author</h2>

    <p>Jeffrey S. Evans  &lt;jeffrey_evans@tnc.org&gt;</p>

    <h2 class="hasAnchor" id="examples"><a class="anchor" href="#examples"></a>Examples</h2>
    <pre class="examples"><div class='input'> <span class='fu'>sa.trans</span><span class='op'>(</span>slope <span class='op'>=</span> <span class='fl'>48.146</span>, aspect <span class='op'>=</span> <span class='fl'>360.000</span><span class='op'>)</span>
</div><div class='output co'>#&gt; [1] -0.2383874</div><div class='input'>
 <span class='kw'><a href='https://rdrr.io/r/base/library.html'>library</a></span><span class='op'>(</span><span class='va'><a href='https://rspatial.org/raster'>raster</a></span><span class='op'>)</span>
 <span class='fu'><a href='https://rdrr.io/r/utils/data.html'>data</a></span><span class='op'>(</span><span class='va'>elev</span><span class='op'>)</span>
 <span class='va'>sa</span> <span class='op'>&lt;-</span> <span class='fu'>raster</span><span class='fu'>::</span><span class='fu'><a href='https://rdrr.io/pkg/raster/man/terrain.html'>terrain</a></span><span class='op'>(</span><span class='va'>elev</span>, opt<span class='op'>=</span><span class='fu'><a href='https://rdrr.io/r/base/c.html'>c</a></span><span class='op'>(</span><span class='st'>"slope"</span>, <span class='st'>"aspect"</span><span class='op'>)</span>, unit<span class='op'>=</span><span class='st'>"degrees"</span><span class='op'>)</span>
 <span class='va'>scosa</span> <span class='op'>&lt;-</span> <span class='fu'>raster</span><span class='fu'>::</span><span class='fu'><a href='https://rdrr.io/pkg/raster/man/overlay.html'>overlay</a></span><span class='op'>(</span><span class='va'>sa</span><span class='op'>[[</span><span class='fl'>1</span><span class='op'>]</span><span class='op'>]</span>, <span class='va'>sa</span><span class='op'>[[</span><span class='fl'>2</span><span class='op'>]</span><span class='op'>]</span>, fun <span class='op'>=</span> <span class='va'>sa.trans</span><span class='op'>)</span>

</div></pre>
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