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<meta property="og:description" content="Creates a point sample that can be used as 
             a NULL for SDM's and other modeling approaches." />




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    <h1>Background sample</h1>
    <small class="dont-index">Source: <a href='https://github.com/jeffreyevans/spatialEco/blob/master/R/background.R'><code>R/background.R</code></a></small>
    <div class="hidden name"><code>background.Rd</code></div>
    </div>

    <div class="ref-description">
    <p>Creates a point sample that can be used as 
             a NULL for SDM's and other modeling approaches.</p>
    </div>

    <pre class="usage"><span class='fu'>background</span><span class='op'>(</span>
  <span class='va'>x</span>,
  ext <span class='op'>=</span> <span class='cn'>NULL</span>,
  p <span class='op'>=</span> <span class='fl'>1000</span>,
  known <span class='op'>=</span> <span class='cn'>NULL</span>,
  d <span class='op'>=</span> <span class='cn'>NULL</span>,
  type <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'>"regular"</span>, <span class='st'>"random"</span>, <span class='st'>"hexagon"</span>, <span class='st'>"nonaligned"</span><span class='op'>)</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>x</th>
      <td><p>A polygon defining sample region</p></td>
    </tr>
    <tr>
      <th>ext</th>
      <td><p>Vector of extent coordinates (xmin, xmax, ymin, ymax)</p></td>
    </tr>
    <tr>
      <th>p</th>
      <td><p>Size of sample</p></td>
    </tr>
    <tr>
      <th>known</th>
      <td><p>SpatialPoints of known locations (same CSR as x)</p></td>
    </tr>
    <tr>
      <th>d</th>
      <td><p>Threshold distance for known proximity</p></td>
    </tr>
    <tr>
      <th>type</th>
      <td><p>Type of sample c("systematic", "random", "hexagon", "nonaligned")</p></td>
    </tr>
    </table>

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

    <p>A SpatialPointsDataFrame or data.frame with x,y coordinates</p>
    <h2 class="hasAnchor" id="note"><a class="anchor" href="#note"></a>Note</h2>

    <p>This function creates a background point sample based on an extent 
or polygon sampling region. The known argument can be used with d 
to remove sample points based on distance-based proximity to existing  
locations (eg., known species locations). The size (p) of the resulting 
sample will be dependent on the known locations and the influence of 
the distance threshold (d). As such, if the know and d arguments are
provided the exact value provided in p will not be returned.</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='kw'><a href='https://rdrr.io/r/base/library.html'>library</a></span><span class='op'>(</span><span class='va'><a href='https://github.com/edzer/sp/'>sp</a></span><span class='op'>)</span>
<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>
</div><div class='output co'>#&gt; <span class='message'></span>
#&gt; <span class='message'>Attaching package: 'raster'</span></div><div class='output co'>#&gt; <span class='message'>The following object is masked from 'package:spatialEco':</span>
#&gt; <span class='message'></span>
#&gt; <span class='message'>    shift</span></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://r-forge.r-project.org/projects/rgeos/'>rgeos</a></span><span class='op'>)</span>
</div><div class='output co'>#&gt; <span class='message'>rgeos version: 0.5-5, (SVN revision 640)</span>
#&gt; <span class='message'> GEOS runtime version: 3.8.0-CAPI-1.13.1 </span>
#&gt; <span class='message'> Linking to sp version: 1.4-5 </span>
#&gt; <span class='message'> Polygon checking: TRUE </span></div><div class='input'>  <span class='fu'><a href='https://rdrr.io/r/utils/data.html'>data</a></span><span class='op'>(</span><span class='va'>meuse</span><span class='op'>)</span>
  <span class='fu'><a href='https://rdrr.io/pkg/sp/man/coordinates.html'>coordinates</a></span><span class='op'>(</span><span class='va'>meuse</span><span class='op'>)</span> <span class='op'>&lt;-</span> <span class='op'>~</span><span class='va'>x</span><span class='op'>+</span><span class='va'>y</span>

<span class='co'># create "known" locations  </span>
<span class='va'>locs</span> <span class='op'>&lt;-</span> <span class='va'>meuse</span><span class='op'>[</span><span class='fu'><a href='https://rdrr.io/r/base/sample.html'>sample</a></span><span class='op'>(</span><span class='fl'>1</span><span class='op'>:</span><span class='fu'><a href='https://rdrr.io/pkg/raster/man/ncell.html'>nrow</a></span><span class='op'>(</span><span class='va'>meuse</span><span class='op'>)</span>, <span class='fl'>5</span><span class='op'>)</span>,<span class='op'>]</span>

<span class='co'># systematic sample using extent polygon</span>
<span class='va'>e</span> <span class='op'>&lt;-</span> <span class='fu'>as</span><span class='op'>(</span><span class='fu'><a href='https://rdrr.io/pkg/raster/man/extent.html'>extent</a></span><span class='op'>(</span><span class='va'>meuse</span><span class='op'>)</span>, <span class='st'>"SpatialPolygons"</span><span class='op'>)</span>
<span class='va'>s</span> <span class='op'>&lt;-</span> <span class='fu'>background</span><span class='op'>(</span><span class='va'>e</span>, p<span class='op'>=</span><span class='fl'>1000</span>, known<span class='op'>=</span><span class='va'>locs</span>, d<span class='op'>=</span><span class='fl'>300</span><span class='op'>)</span>
  <span class='fu'><a href='https://rdrr.io/pkg/raster/man/plot.html'>plot</a></span><span class='op'>(</span><span class='va'>s</span>,pch<span class='op'>=</span><span class='fl'>20</span><span class='op'>)</span>
</div><div class='input'>    <span class='fu'><a href='https://rdrr.io/r/graphics/points.html'>points</a></span><span class='op'>(</span><span class='va'>locs</span>, pch<span class='op'>=</span><span class='fl'>20</span>, col<span class='op'>=</span><span class='st'>"red"</span><span class='op'>)</span>
</div><div class='img'><img src='background-1.png' alt='' width='700' height='433' /></div><div class='input'>
<span class='co'># systematic sample using irregular polygon</span>
<span class='fu'><a href='https://rdrr.io/r/utils/data.html'>data</a></span><span class='op'>(</span><span class='va'>meuse.grid</span><span class='op'>)</span>
  <span class='fu'><a href='https://rdrr.io/pkg/sp/man/coordinates.html'>coordinates</a></span><span class='op'>(</span><span class='va'>meuse.grid</span><span class='op'>)</span> <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'>"x"</span>, <span class='st'>"y"</span><span class='op'>)</span>
  <span class='fu'><a href='https://rdrr.io/pkg/sp/man/gridded-methods.html'>gridded</a></span><span class='op'>(</span><span class='va'>meuse.grid</span><span class='op'>)</span> <span class='op'>=</span> <span class='cn'>TRUE</span>
<span class='va'>meuse.poly</span> <span class='op'>=</span> <span class='fu'><a href='https://rdrr.io/pkg/rgeos/man/topo-bin-gUnion.html'>gUnaryUnion</a></span><span class='op'>(</span><span class='fu'>as</span><span class='op'>(</span><span class='va'>meuse.grid</span>, <span class='st'>"SpatialPolygons"</span><span class='op'>)</span><span class='op'>)</span>

<span class='va'>s</span> <span class='op'>&lt;-</span> <span class='fu'>background</span><span class='op'>(</span><span class='va'>meuse.poly</span>, p<span class='op'>=</span><span class='fl'>1000</span>, known<span class='op'>=</span><span class='va'>locs</span>, d<span class='op'>=</span><span class='fl'>200</span><span class='op'>)</span>
  <span class='fu'><a href='https://rdrr.io/pkg/raster/man/plot.html'>plot</a></span><span class='op'>(</span><span class='va'>s</span>,pch<span class='op'>=</span><span class='fl'>20</span><span class='op'>)</span>
</div><div class='input'>    <span class='fu'><a href='https://rdrr.io/pkg/raster/man/plot.html'>plot</a></span><span class='op'>(</span><span class='va'>meuse.poly</span>, add<span class='op'>=</span><span class='cn'>TRUE</span><span class='op'>)</span>
</div><div class='input'>    <span class='fu'><a href='https://rdrr.io/r/graphics/points.html'>points</a></span><span class='op'>(</span><span class='va'>locs</span>, pch<span class='op'>=</span><span class='fl'>20</span>, col<span class='op'>=</span><span class='st'>"red"</span><span class='op'>)</span>
</div><div class='img'><img src='background-2.png' alt='' width='700' height='433' /></div><div class='input'>
<span class='co'># random sample using irregular polygon</span>
<span class='va'>s</span> <span class='op'>&lt;-</span> <span class='fu'>background</span><span class='op'>(</span><span class='va'>meuse.poly</span>, p<span class='op'>=</span><span class='fl'>500</span>, known<span class='op'>=</span><span class='va'>locs</span>, 
                d<span class='op'>=</span><span class='fl'>200</span>, type<span class='op'>=</span><span class='st'>"random"</span><span class='op'>)</span>
  <span class='fu'><a href='https://rdrr.io/pkg/raster/man/plot.html'>plot</a></span><span class='op'>(</span><span class='va'>s</span>,pch<span class='op'>=</span><span class='fl'>20</span><span class='op'>)</span>
</div><div class='input'>    <span class='fu'><a href='https://rdrr.io/pkg/raster/man/plot.html'>plot</a></span><span class='op'>(</span><span class='va'>meuse.poly</span>, add<span class='op'>=</span><span class='cn'>TRUE</span><span class='op'>)</span>
</div><div class='input'>    <span class='fu'><a href='https://rdrr.io/r/graphics/points.html'>points</a></span><span class='op'>(</span><span class='va'>locs</span>, pch<span class='op'>=</span><span class='fl'>20</span>, col<span class='op'>=</span><span class='st'>"red"</span><span class='op'>)</span>
</div><div class='img'><img src='background-3.png' alt='' width='700' height='433' /></div><div class='input'>
<span class='co'># systematic sample using defined extent</span>
<span class='fu'><a href='https://rdrr.io/pkg/raster/man/extent.html'>extent</a></span><span class='op'>(</span><span class='va'>meuse</span><span class='op'>)</span>
</div><div class='output co'>#&gt; class      : Extent 
#&gt; xmin       : 178605 
#&gt; xmax       : 181390 
#&gt; ymin       : 329714 
#&gt; ymax       : 333611 </div><div class='input'><span class='va'>s</span> <span class='op'>&lt;-</span> <span class='fu'>background</span><span class='op'>(</span>ext<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='fl'>178605</span>, <span class='fl'>181390</span>, <span class='fl'>329714</span>, <span class='fl'>333611</span><span class='op'>)</span>, 
                p<span class='op'>=</span><span class='fl'>1000</span>, known<span class='op'>=</span><span class='va'>locs</span>, d<span class='op'>=</span><span class='fl'>300</span><span class='op'>)</span>
  <span class='fu'><a href='https://rdrr.io/pkg/raster/man/plot.html'>plot</a></span><span class='op'>(</span><span class='va'>s</span>,pch<span class='op'>=</span><span class='fl'>20</span><span class='op'>)</span>
</div><div class='input'>    <span class='fu'><a href='https://rdrr.io/r/graphics/points.html'>points</a></span><span class='op'>(</span><span class='va'>locs</span>, pch<span class='op'>=</span><span class='fl'>20</span>, col<span class='op'>=</span><span class='st'>"red"</span><span class='op'>)</span>
</div><div class='img'><img src='background-4.png' alt='' width='700' height='433' /></div><div class='input'>
</div></pre>
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