title: Is there any way to create blurred countour without scattered data in d3?
body: <p>The goal is creating blurred contour without scattered data. Image is here
  <a href="https://i.stack.imgur.com/ndB5y.png" rel="nofollow noreferrer">enter image description here</a></p>
  <p>If I have data array like</p>
  <pre><code>let data = [
        [16, null, null, null, null],
        [null, null, null, null, 15],
        [6, null, 12, null, null],
        [null, 8, null, null, null],
        [null, null, null, null, 10]
      ]
  </code></pre>
  <p>D3 contour requires scatted data like</p>
  <pre><code>let data = [
        [16, 8, 4, 3, 5],
        [14, 5, 7, 8, 15],
        [6, 10, 12, 9, 12],
        [20, 8, 11, 3, 4],
        [15, 14, 0, 14, 10]
      ]
  </code></pre>
  <p>This means I should fill blank(null) data to something, but it's not awesome.</p>
  <p>So, is there supported method to parse automatically 'none scattered data' to 'scattered data' in d3?</p>
  <p>Or, custom method to calculate near data?</p>
  <p>More detail like below</p>
  <pre><code>let data = [
        [a, null, null, null, null],
        [null, null, null, null, null],
        [null, null, null, null, null],
        [null, null, null, null, null],
        [null, null, null, null, b]
      ]
  </code></pre>
  <p>to</p>
  <pre><code>let data = [
        [a+(b-8), (a-1)+(b-7), (a-2)+(b-6), (a-3)+(b-5), (a-4)+(b-4)],
        [(a-1)+(b-7), (a-2)+(b-6), (a-3)+(b-5), (a-4)+(b-4), (a-5)+(b-3)],
        [(a-2)+(b-6), (a-3)+(b-5), (a-4)+(b-4), (a-5)+(b-3), (a-6)+(b-2)],
        [(a-3)+(b-5), (a-4)+(b-4), (a-5)+(b-3), (a-6)+(b-2), (a-7)+(b-1)],
        [(a-4)+(b-4), (a-5)+(b-3), (a-6)+(b-2), (a-7)+(b-1), (a-8)+b]
      ]
  </code></pre>
  <p>Any opinion would be appreciated, thanks.</p>