; elevationData[offset];
      pixel[1] &#x3D; elevationData[offset + 1];
      pixel[2] &#x3D; elevationData[offset + 2];
      pixel[3] &#x3D; elevationData[offset + 3];
      z0 &#x3D; data.vert * (pixel[0] + pixel[1] * 2 + pixel[2] * 3);

      // determine elevation for (x1, pixelY)
      offset &#x3D; (pixelY * width + x1) * 4;
      pixel[0] &#x3D; elevationData[offset];
      pixel[1] &#x3D; elevationData[offset + 1];
      pixel[2] &#x3D; elevationData[offset + 2];
      pixel[3] &#x3D; elevationDa