title: Calculating polygon intersecting area with gArea and gIntersection error in R
body: <p>I have two polygons</p>
  <pre><code>coords1[,1]
  -15.99719 -16.01133 -16.04000 -16.08308 -16.14041 -16.21175 -16.29681 -16.39525 -16.50668 -16.63064 -16.76664 -16.91413 -17.07252 -17.24116 -17.41939 -17.60647 -17.80166 -18.00417 -18.21319 -18.42788 -18.64736 -18.87076 -19.09718 -19.32570 -19.55541 -19.78538 -20.01468 -20.24240 -20.46760 -20.68940 -20.90688 -21.11919 -21.32546 -21.52486 -21.71659 -21.89988 -22.07399 -22.23822 -22.39191 -22.53443 -22.66522 -22.78374 -22.88953 -22.98215 -23.06124 -23.12646 -23.17757 -23.21435 -23.23666 -23.24441 -23.23756 -23.21615 -23.18025 -23.13002 -23.06566 -22.98742 -22.89562 -22.79063 -22.67288 -22.54283 -22.40101 -22.24800 -22.08440 -21.91088 -21.72813 -21.53690 -21.33795 -21.13208-20.92012 -20.70293 -20.48137 -20.25635 -20.02876 -19.79953 -19.56958 -19.33983 -19.11120 -18.88463 -18.66102 -18.44127 -18.22626 -18.01687 -17.81393 -17.61826 -17.43066 -17.25187 -17.08262 -16.92358 -16.77540 -16.63868 -16.51396 -16.40174 -16.30249 -16.21659 -16.14440 -16.08620 -16.04224 -16.01268 -15.99764 -15.99719
  
  
  coords1[,2]
  6.225418 6.262789 6.300443 6.338229 6.375996 6.413591 6.450863 6.487662 6.523839 6.559250 6.593750 6.627202 6.659471 6.690426 6.719943 6.747904 6.774196 6.798712 6.821354 6.842031 6.860660 6.877166 6.891481 6.903550 6.913322 6.920758 6.925830 6.928515 6.928804 6.926696 6.922198 6.915329 6.906116 6.894597 6.880818 6.864834 6.846711 6.826520 6.804343 6.780269 6.754396 6.726828 6.697675 6.667055 6.635091 6.601912 6.567652 6.532448 6.496442 6.459780 6.422608 6.385077 6.347338 6.309542 6.271842 6.234389 6.197335 6.160829 6.125017 6.090044 6.056051 6.023174 5.991546 5.961295 5.932541 5.905401 5.879985 5.856394 5.834723 5.815060 5.797484 5.782066 5.768867 5.757941 5.749333 5.743075 5.739195 5.737707 5.738617 5.741922 5.747609 5.755654 5.766025 5.778680 5.793569 5.810631 5.829798 5.850993 5.874129 5.899115 5.925849 5.954224 5.984126 6.015434 6.048021 6.081758 6.116508 6.152130 6.188483 6.225418
  
  coords1.sys[,1]
  -17.27076 -17.28943 -17.32370 -17.37346 -17.43849 -17.51853 -17.61326 -17.72229 -17.84520 -17.98148 -18.13059 -18.29192 -18.46483 -18.64862 -18.84254 -19.04583 -19.25765 -19.47717 -19.70348 -19.93569 -20.17285 -20.41402 -20.65821 -20.90445 -21.15175 -21.39911 -21.64554 -21.89003 -22.13161 -22.36931 -22.60216 -22.82924 -23.04962 -23.26241 -23.46677 -23.66187 -23.84692 -24.02117 -24.18394 -24.33455 -24.47241 -24.59695 -24.70769 -24.80416 -24.88599 -24.95284 -25.00445 -25.04060 -25.06116 -25.06603 -25.05520 -25.02871 -24.98667 -24.92926 -24.85668 -24.76926 -24.66732 -24.55129 -24.42163 -24.27886 -24.12357 -23.95636 -23.77792 -23.58897 -23.39027 -23.18261 -22.96683 -22.74380 -22.51443 -22.27962 -22.04034 -21.79754 -21.55219 -21.30530 -21.05785 -20.81083 -20.56525 -20.32209 -20.08233 -19.84693 -19.61685 -19.39301 -19.17632 -18.96763 -18.76781 -18.57764 -18.39789 -18.22930 -18.07253 -17.92822
  -17.79696 -17.67926 -17.57560 -17.48640 -17.41203 -17.35277 -17.30887 -17.28050 -17.26778 -17.27076
  
  coords1.sys[,2]
  6.465179 6.538004 6.611223 6.684541 6.757663 6.830295 6.902143 6.972919 7.042338 7.110120 7.175992 7.239689 7.300955 7.359542 7.415215 7.467750 7.516935 7.562573 7.604478 7.642483 7.676435 7.706197 7.731648 7.752688 7.769230 7.781208 7.788574 7.791299 7.789371 7.782798 7.771606 7.755841 7.735567 7.710864 7.681832 7.648589 7.611267 7.570018 7.525007 7.476416 7.424440 7.369288 7.311183 7.250359 7.187060 7.121542 7.054068 6.984910 6.914346 6.842661 6.770143 6.697084 6.623779 6.550522 6.477608 6.405332 6.333984 6.263851 6.195216 6.128355 6.063538 6.001025 5.941069 5.883910 5.829778 5.778892 5.731457 5.687664 5.647688 5.611692 5.579819 5.552199 5.528941 5.510141 5.495874 5.486197 5.481149 5.480751 5.485003 5.493890 5.507375 5.525404 5.547904 5.574784 5.605938 5.641238 5.680543 5.723695 5.770520 5.820829 5.874419 5.931076 5.990571 6.052663 6.117104 6.183634 6.251984 6.321880 6.393041 6.465179
  
  
  plot(1,1,ylim=c(0,15),xlim=c(-30,-10), t=&quot;n&quot;, xlab=&quot;&quot;, ylab=&quot;&quot;)
  polygon(coords1[,1], coords1[,2], border=2,col=alpha(&quot;red&quot;,0.5))
  polygon(coords1.sys[,1], coords1.sys[,2], border=2,col=alpha(&quot;black&quot;,0.5))
  </code></pre>
  <p><a href="https://i.stack.imgur.com/8BEDt.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8BEDt.png" alt="enter image description here" /></a></p>
  <p>I am trying to calculate the percent overlap, as shown using gArea and gIntersection <a href="https://stackoverflow.com/questions/35039614/r-calculate-overlapping-section-polygon-intersection-the-fast-way">here</a>.</p>
  <pre><code>kt.small.g=data.frame(coords1[,1], coords1[,2])
  names(kt.small.g)=c(&quot;x&quot;,&quot;y&quot;)
  summary(kt.small.g)
  
  kt.small.s=data.frame(coords1.sys[,1], coords1.sys[,2])
  names(kt.small.s)=c(&quot;x&quot;,&quot;y&quot;)
  kt.small.g_pol &lt;- Polygons(list(Polygon(kt.small.g)), &quot;small.g&quot;)
  kt.small.s_pol &lt;- Polygons(list(Polygon(kt.small.s)), &quot;small.s&quot;)
  
  kt.small.g_area &lt;- gArea(shape[&quot;small.g&quot;])
  kt.small.intersections &lt;- gIntersection(shape[&quot;small.g&quot;], shape[&quot;small.s&quot;])
  
  </code></pre>
  <p>but after running <code>kt.small.g_area &lt;- gArea(shape[&quot;small.g&quot;])</code> or <code>kt.small.intersections &lt;- gIntersection(shape[&quot;small.g&quot;], shape[&quot;small.s&quot;])</code> I get the error:</p>
  <pre><code>Error in h(simpleError(msg, call)) : 
    error in evaluating the argument 'obj' in selecting a method for function 'is.projected': NAs not permitted in row index
  </code></pre>
  <p>I have run through the code in the linked example without error. I have checked my data for NAs, parallel structure to the example, and tried to change the names in <code>shape[]</code> to smaller strings or strings without &quot;.&quot; and I still get the same error.</p>
  <p>Thank you for your help.</p>