Failed to load a mesh from gptoolbox. I am missing something, what is it?

% 1. Load a Mesh
[V, F] = readOFF('D:\Conferences and Workshops\SG Summer\MFC - S\codes\gptoolbox-master\gptoolbox-master\mesh.off');

% 2. Display the Mesh
figure;
trisurf(F, V(:,1), V(:,2), V(:,3), 'FaceColor', 'cyan', 'EdgeColor', 'none');
axis equal;
lighting gouraud;
camlight;
title('Original Mesh');
xlabel('X');
ylabel('Y');
zlabel('Z');

% Define the number of iterations and timestep for smoothing
num_iterations = 100;
time_step = 0.01;

% 3. Mean Curvature Flow (MCF) - Explicit Method
V_explicit = V; % Copy the vertices for the explicit method

for iter = 1:num_iterations
    % Compute the Laplace-Beltrami operator and mean curvature normal
    L = cotmatrix(V_explicit, F);
    HN = -L * V_explicit;
    
    % Update vertex positions
    V_explicit = V_explicit + time_step * HN;
end

% Display the smoothed mesh - Explicit Method
figure;
trisurf(F, V_explicit(:,1), V_explicit(:,2), V_explicit(:,3), 'FaceColor', 'cyan', 'EdgeColor', 'none');
axis equal;
lighting gouraud;
camlight;
title('MCF - Explicit Method');
xlabel('X');
ylabel('Y');
zlabel('Z');

% 3. Mean Curvature Flow (MCF) - Semi-Implicit Method
V_implicit = V; % Copy the vertices for the implicit method

for iter = 1:num_iterations
    % Compute the Laplace-Beltrami operator
    L = cotmatrix(V_implicit, F);
    
    % Solve (I - time_step * L) * V_new = V_old
    V_implicit = (speye(size(V_implicit, 1)) - time_step * L) \ V_implicit;
end

% Display the smoothed mesh - Semi-Implicit Method
figure;
trisurf(F, V_implicit(:,1), V_implicit(:,2), V_implicit(:,3), 'FaceColor', 'cyan', 'EdgeColor', 'none');
axis equal;
lighting gouraud;
camlight;
title('MCF - Semi-Implicit Method');
xlabel('X');
ylabel('Y');
zlabel('Z');

here is the link to loadmesh function: https://github.com/geometry-processing/gptoolbox/blob/master/mesh/load_mesh.m

and the readOFF: https://github.com/geometry-processing/gptoolbox/blob/master/mesh/readOFF.m

I get this error:

shittyday (%sorry this is the name of the script)
Error using fscanf
Invalid file identifier. Use fopen to generate a valid file identifier.

Error in readOFF (line 27)
  OFFheader = upper(fscanf( fp, '%s\n', 1 ));

Error in shittyday (line 2)
[V, F] = readOFF('D:\Conferences and Workshops\SG Summer\MFC - S\codes\gptoolbox-master\gptoolbox-master\mesh.off');
 

[Walter Roberson]

Do you get an error message?

[ehsan]

Yes, I forgot to put that in the main body of the question edited it now @Walter Roberson

[Vinay]

Hello Eshan,

I tried running the code on an irregular polyhedron (.off file) and it is working correctly. Could you please provide more details about the error you are encountering?

[Vinay]

Can you share the 'mesh.off' file ?

[ehsan]

Hello @Vinay It is here on this git: https://github.com/geometry-processing/gptoolbox/blob/master/mesh/readOFF.m

I will put it there too:

function [V,F,UV,C,N] = readOFF( filename )
  % READOFF reads an OFF file with vertex/face information
  %
  % [V,F,UV,C,N] = readOFF( filename )
  %
  % Input:
  %  filename  path to .off file
  % Outputs:
  %  V  #V by 3 list of vertices
  %  F  #F by 3 list of triangle indices
  %  UV  #V by 2 list of texture coordinates
  %  C  #V by 3 list of colors
  %  N  #V by 3 list of normals
  %
  % See also: load_mesh, readOBJfast, readOBJ

% (C) 2007 Denis Kovacs, NYU
%-------------------------------------------------------------------------

  V = [];
  F = [];
  UV = [];
  C = [];
  N = [];
  
  fp = fopen( filename, 'r' );
  OFFheader = upper(fscanf( fp, '%s\n', 1 ));
  if OFFheader(end-2:end) ~= 'OFF'
    warning('no OFF file!') 
    fclose(fp);
    return;
  end
  OFFdim = 3;
  OFF_N = 0; OFF_C=0; OFF_ST=0;
  
  if find(OFFheader=='N') OFFdim = OFFdim+3; OFF_N=1; end
  if find(OFFheader=='C') OFFdim = OFFdim+3; OFF_C=1; end
  if find(OFFheader=='S') OFFdim = OFFdim+2; OFF_ST=1; end

  % eat any comments before
  line = eat_comments(fp,'#');
  
  d = sscanf( line, '%d', 3);
  nV = d(1); nF = d(2); nE = d(3);
  
  %disp(sprintf('  - Reading %d vertices', nV));
  
  switch OFFdim
      case  3; OFFV = textscan( fp, '%f %f %f', nV);
      case  5; OFFV = textscan( fp, '%f %f %f %f %f', nV);
      case  6; OFFV = textscan( fp, '%f %f %f %f %f %f', nV);
      case  7; OFFV = textscan( fp, '%f %f %f %f %f %f %f', nV);
      case  8; OFFV = textscan( fp, '%f %f %f %f %f %f %f %f', nV);
      case  9; OFFV = textscan( fp, '%f %f %f %f %f %f %f %f %f', nV);
      case 10; OFFV = textscan( fp, '%f %f %f %f %f %f %f %f %f %f', nV);
      case 11; OFFV = textscan( fp, '%f %f %f %f %f %f %f %f %f %f %f', nV);
      otherwise; fclose(fp); error('Unsupported number of vertex entries');
  end
  
  try
     OFFV = cell2mat(OFFV); 
  end
  
  OFFdim = 1;
  V = OFFV(:,OFFdim:(OFFdim+2)); OFFdim = OFFdim + 3;
  if (OFF_N) N = OFFV(:,OFFdim:(OFFdim+2)); OFFdim = OFFdim + 3; end
  if (OFF_C) C = OFFV(:,OFFdim:(OFFdim+2)); OFFdim = OFFdim + 3; end
  if (OFF_ST) UV = OFFV(:,OFFdim:(OFFdim+1)); OFFdim = OFFdim + 2; end
  
  if (nF ~= 0)
    %disp(sprintf('  - Reading %d faces', nF));
    temp = textscan( fp, '%d %d %d %d %d %d %d %d %d %d %d', nF );
    sz = temp{1}(1);
    if all(sz == cell2mat(temp(1)))
      F = double (cell2mat( temp(2:sz+1 ))) +1;
    else
      warning('Trivially triangulating high degree facets');
      F = zeros(sum(temp{1}-2),3);
      fi = 1;
      for f = 1:size(temp{1},1)
        for j = 3:temp{1}(f);
          F(fi,:) = [temp{2}(f) temp{j}(f) temp{j+1}(f)]+1;
          fi = fi+1;
        end
      end
    end
  else
    F = [];
  end

  fclose(fp);
  
  %disp('  - done.');
end

am I loading the data correctly?

[Vinay]

Try adding this command in the readoff.m file to check if 'fopen' is opening the file correctly or not

fp = fopen( filename, 'r' );
if fp == -1
    error('Failed to open file: %s', filename);
end
OFFheader = upper(fscanf( fp, '%s\n', 1 ));

[ehsan]

@Vinay You are correct, it doesn't open. It says:

Error using readOFF

Failed to open file

[Vinay]

@ehsan The file 'mesh.off' might not be present in the current folder or the path name may be wrong.

Also share the 'mesh.off' file you are trying to open

[ehsan]

Aha! - I think the path is correct .. Here is the load_mesh.m

function [V,F] = load_mesh(filename,varargin)
  % read in vertices and faces from a .off or .obj file
  % 
  % [V,F] = load_mesh(filename)
  % [V,F] = load_mesh(filename,'ParameterName',ParameterValue, ...)
  %
  % Input:
  %   filename  file holding mesh
  %   Optional:
  %     'Quiet' followed by whether to be quiet {false}
  % Output:
  %   V (vertex list) 
  %   F (face list) fields
  %
  % Copyright 2011, Alec Jacobson ([e-mail])
  %
  % See also: readOBJ, readOBJfast, readOFF
  %

  % parse any optional input
  v = 1;
  quiet = false;
  while(v <= numel(varargin))
    switch varargin{v}
    case 'Quiet'
      v = v+1;
      assert(v<=nargin);
      quiet = varargin{v};
      quiet = quiet * 1;
    otherwise
      error(['Unsupported parameter: ' varargin{v}]);
    end
    v = v + 1;
  end

  % if mex libigl reader exists use that (up to 25x faster for .obj)
  if exist('read_triangle_mesh','file')==3
    try
      [V,F] = read_triangle_mesh(GetFullPath(filename));
      if ~isempty(V) && ~isempty(F)
        return;
      end
      % else keep trying below
    catch e
      warning(e.message);
      % else keep trying below
    end
  end
  
  [~,~,ext] = fileparts(filename);
  ext = lower(ext);
  switch ext
  case '.3ds'
    [V,F] = read3DS(filename);
  case '.obj'
    try
      [V,F] = readOBJfast(filename);
    catch exception
      if ~quiet
        fprintf('Fast reader failed, retrying with more robust, slower reader\n');
      end
      [V,F] = readOBJ(filename);
    end
  case '.off'
    [V,F] = readOFF(filename);
  case '.ply'
    [V,F] = readPLY(filename);
  case '.stl'
    [V,F] = readSTL(filename);
  case '.wrl'
    [V,F] = readWRL(filename);
  case '.xml'
    [V,F] = read_mesh_from_xml(filename);
  otherwise
    error('Unknown mesh format: %s',ext);
  end
end

[Vinay]

@ehsan I have attached a 'face.zip' file containig the face.off file and the 'demo.m' which is loading the mesh.

Try to run this script and if you face any issue please tell me.

Also can you share this 'D:\Conferences and Workshops\SG Summer\MFC - S\codes\gptoolbox-master\gptoolbox-master\mesh.off' file you are trying to load in your script.

[ehsan]

@VinayYour demo worked and gave this output

[ehsan]

@Vinay oh, I think there is not any filename.off in the gptoolbox package I downloaded. The package is on this git: https://github.com/geometry-processing/gptoolbox/tree/master

Answer 1

[Vinay]

Hii eshan,

The issue is due to the filename is incorrect or not present.You can use the correct file while loading the data in the "load_mesh" function.

You can use different "off" files from the given link

https://people.sc.fsu.edu/~jburkardt/data/off/off.html

I hope this helps!

[ehsan]

Hi @Vinay oh yes it helped me so much! thank you!