libigl_Martin/python/204_Gradient.py

import igl

V = igl.eigen.MatrixXd()
F = igl.eigen.MatrixXi()

# Load a mesh in OFF format
igl.readOFF("../tutorial/shared/cheburashka.off", V, F)

# Read scalar function values from a file, U: #V by 1
U = igl.eigen.MatrixXd()
igl.readDMAT("../tutorial/shared/cheburashka-scalar.dmat",U)
U = U.col(0)

# Compute gradient operator: #F*3 by #V
G = igl.eigen.SparseMatrixd()
igl.grad(V,F,G)


# Compute gradient of U
GU = (G*U).MapMatrix(F.rows(),3)

# Compute gradient magnitude
GU_mag = GU.rowwiseNorm()


  # igl::viewer::Viewer viewer;
  # viewer.data.set_mesh(V, F);

# Compute pseudocolor for original function
C = igl.eigen.MatrixXd()

igl.jet(U,True,C)

#
# # Or for gradient magnitude
# # igl.jet(GU_mag,True,C)
#
#   # viewer.data.set_colors(C);
#
# # Average edge length divided by average gradient (for scaling)
# max_size = igl.avg_edge_length(V,F) / GU_mag.mean()
#
# # Draw a black segment in direction of gradient at face barycenters
# BC = igl.eigen.MatrixXd()
# igl.barycenter(V,F,BC)

  # const RowVector3d black(0,0,0);
  # viewer.data.add_edges(BC,BC+max_size*GU, black);
  #
  # // Hide wireframe
  # viewer.core.show_lines = false;
  #
  # viewer.launch();