MATLAB Answers

implementation of subclass from triangulation

4 views (last 30 days)
Hi everyone,
I am trying to implement a derived class from the 'triangulation' class available in Matlab 2014. The aim is to introduce additional properties and methods. I tried to mimic the example available in the Matlab documentation, but I failed even in creating a simple constructor. The minimal example is the following
classdef mymesh < triangulation
properties
Obj = [];
end
methods
% constructor
function primal = mymesh(P,T,M) % M is the object code
primal = primal@triangulation(T,P);
primal.Obj = M;
end
end
end
But trying to call it with the code
P = [0 0 0; 0 1 0; 1 1 0; 1 1 1];
T = [1 2 3 4];
M = ones(size(T,1),1);
c = mymesh(P,T,M);
makes Matlab crash. Can anyone point my were I am wrong?
Thank you in advance
Fabio

  1 Comment

Fabio Freschi
Fabio Freschi on 19 Jan 2016
The crash happens in Matlab 2014b. With version 2015b the error message is:
Class 'mymesh' is not an allowed subclass of class 'triangulation'.

Sign in to comment.

Accepted Answer

Tom Clark
Tom Clark on 6 Jul 2016
Edited: Tom Clark on 6 Jul 2016
Fabio,
To follow up on Rebecca's (correct, IMO) answer, you can overload properties and methods of the triangulation class, to make your new class look exactly like a triangulation.
classdef MyTri
properties(Hidden = true)
TR
end
properties(Dependent)
Points
ConnectivityList
end
methods
function obj = MyTri(varargin)
% your constructor here, which creates a triangulation and stores it in obj.TR
end
function p = get.Points(obj)
% Property getter method, so that MyTri.Points behaves like triangulation.Points
p = obj.TR.Points;
end
function c = get.ConnectivityList(obj)
% Another property getter
c = obj.TR.ConnectivityList;
end
end
end
If you're familiar with python, using the dependent property with a getter is similar to using python's @property decorator on a class method (I'm a MATLAB guy but have to admit that python deals with this way more elegantly).
You may also wish to add a custom isa() method, to return true for both 'MyTri' and 'triangulation' objects in a fashion consistent with the application of isa() to a subclass. I've left that out here, because of course this isn't strictly a subclass.
Adding set.Points and set.ConnectivityList methods (very similar syntax to the getters example above) will allow you to modify your triangulation as normal, if that's what you require.
Finally, having done this myself, I have a bunch of methods to overload the triangulation class methods, just by passing variables through. To save anyone the unbelievable nuisance of duplicating this work, here they are (Caveat emptor: My unit tests don't have 100% coverage yet, so please test them as you use them!):
% Overload all the triangulation class methods for this class
function PC = barycentricToCartesian(obj, ti, B)
PC = barycentricToCartesian(obj.TR, ti, B);
end
function B = cartesianToBarycentric(obj, ti, PC)
B = cartesianToBarycentric(obj.TR, ti, PC);
end
function [CC, r] = circumcenters(obj, varargin)
[CC,r] = circumcenters(obj.TR, varargin{:});
end
function ti = edgeAttachments(obj, varargin)
ti = edgeAttachments(obj.TR, varargin{:});
end
function E = edges(obj)
E = edges(obj.TR);
end
function FN = faceNormal(obj, varargin)
FN = faceNormals(obj.TR, varargin{:});
end
function FE = featureEdges(obj, filterangle)
FE = featureEdges(obj.TR, filterangle);
end
function [FBtri, FBpoints] = freeBoundary(obj)
[FBtri, FBpoints] = freeBoundary(obj.TR);
end
function [IC,r] = incenter(obj,ti)
[IC,r] = incenter(obj.TR,ti);
end
function [tf] = isConnected(obj,varargin)
tf = isConnected(obj.TR,varargin{:});
end
function [vi,d] = nearestNeighbor(obj,varargin)
[vi,d] = nearestNeighbour(obj.TR,varargin{:});
end
function N = neighbors(obj, varargin)
N = neighbors(obj.TR, varargin{:});
end
function SZ = size(obj)
SZ = size(obj.TR);
end
function ti = vertexAttachments(obj, varargin)
ti = vertexAttachments(obj.TR, varargin{:});
end
function VN = vertexNormal(obj,varargin)
VN = vertexNormal(obj.TR,varargin{:});
end
Hope this helps, please upvote me if it does :)
Tom

  1 Comment

Carl Holmberg
Carl Holmberg on 2 Oct 2018
I have used this code and greatly apreaciate it! One can note that there is an "s" added to the end of the function call:
faceNormals(obj.TR, varargin{:});

Sign in to comment.

More Answers (2)

Rebecca Krosnick
Rebecca Krosnick on 20 Jan 2016
It seems that we cannot create a subclass of "triangulation". Instead, you can create a class that has a "triangulation" object as a property rather than creating a subclass of "triangulation".

  2 Comments

Fabio Freschi
Fabio Freschi on 20 Jan 2016
Thanks Rebecca, my question is: to access the points the syntax will be
mymesh.TR.Points
won't it?
Tom Clark
Tom Clark on 6 Jul 2016
Yes it will. I've extended Rebecca's answer below to address this with a full example.

Sign in to comment.


per isakson
per isakson on 21 Jan 2016
Edited: per isakson on 21 Jan 2016
You are too kind to Matlab. Matlab shall not crash whether or not you make a mistake. Now I crashed R2013b a couple of time with your code. I assume you need to ask support.
However, you might want to try this
P = [0 0 0; 0 1 0; 1 1 0; 1 1 1];
T = [1 2 3 4];
M = ones(size(T,1),1);
tr = triangulation(T,P);
mym = mymesh(tr,M);
mym.TR.Points
outputs
ans =
0 0 0
0 1 0
1 1 0
1 1 1
where
classdef mymesh < handle
properties
Obj = [];
TR
end
methods
% constructor
function primal = mymesh( tr, M ) % M is the object code
primal.Obj = M;
primal.TR = tr;
end
end
end

  3 Comments

Fabio Freschi
Fabio Freschi on 22 Jan 2016
It works but its use is weird: Statements like
mym.TR.Points
are effective but I see it as a workaround rather than a solution. I agree with you that Matlab should not crash. Anyway the bug seems to be fixed in 2015b.
Thank you for your support
Fabio
Arabarra
Arabarra on 8 Nov 2016
it's still weird that one should need to use composition instead of subclassing. TriRep (the predecessor of triangulation) used to allow subclassing (till R2016b)

Sign in to comment.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!