title: how to plot 3D mesh to depth map
body: <p>I have a 3d triangle mesh</p>
  <pre><code>from torch_geometric.data import Data
  </code></pre>
  <p>want to plot it as depth map from top view, so the pixel value of (x,y) equals depth value.</p>
  <p>there is a piece of code to plot, but I don't know how to calculate z value for each pair of (x,y)</p>
  <pre><code>plt.subplot()
  x = data.x[:,1]
  y = data.x[:,0]
  X, Y = np.meshgrid(x, y)
  plt.pcolor(data.x[:,1], data.x[:,0], data.x[:,2] * 255, cmap='RdBu', vmin=0, vmax=255)
  </code></pre>