fix(vtk): transpose vector before numpy_to_vtk (#2733)

add_vector() assigns a vector to each grid cell. The method takes an array of shape (3, nnodes) and passes it to numpy_support.numpy_to_vtk(), which due to the order of indices flattens it in column-major order, but VTK expects row-major order.

So where cell i should get

(x[i], y[i], z[i])

it instead gets

(x[3i], x[3i+1], x[3i+2])

Fixed by transposing the array passed to numpy_to_vtk() so it is (nnodes, 3) and is flattened/interpreted correctly

Author: wpbonelli

flopy/export/vtk.py

@@ -897,7 +897,7 @@ def add_vector(self, vector, name, masked_values=None):
             else:
                 raise AssertionError("Size of vector must be 3 * nnodes or 3 * ncpl")
         else:
-            vector = np.reshape(vector, (3, self.nnodes))
+            vector = np.reshape(vector, (3, self.nnodes)).T
 
         if self.point_scalars:
             tmp = []