title: QGIS field calculator interpolating over raster
body: <p>I want to add a z field to my shapefile. Z value is the elevation of the center of the basin. I wonder how should I acomplish that. x and y values of the centroids are in the table. I have the dem of the region.</p>
  <p><a href="https://i.stack.imgur.com/HhLc4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HhLc4.png" alt="enter image description here" /></a></p>