/span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># Extract a single 3D volume</span></span></span>
<span class="r-in"><span><span class="va">first_volume</span> <span class="op">&lt;-</span> <span class="va">dense_vec</span><span class="op">[[</span><span class="fl">1</span><span class="op">]</span><span class="op">]</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># Create a