finding curvature of plot

i started with calling out my txt file this way:

[z,x,y] = textread ('D:\Matlab\315 Big.txt' ,'%f %f %f', 100); or 
load('D:\Matlab\315 Big.txt');or
M =load('D:\Matlab\315 Big.txt');

and then i continue on with the whole page of function for curvature following the link. however it prompts:function k=LineCurvature2D(Vertices,Lines) ↑ Error: Function definition not supported in this context. Create functions in code file.

how should i proceed? i am totally clueless about Matlab.

[KSSV]

YOu already asked this question thrice..:( I gave you working solution also.

   Vertices =load(''D:\Matlab\315 Big.txt');
      Vertices(:,1) = [] ;   % because all zeros     
      k=LineCurvature2D(Vertices) ;

Still you posted the same question..? :(

What version you are using? See to it that, the function is in the present working directory.

[Bruno Luong]

KSSV: He doesn't know what "working directory" is, and I'm not sure he knows how to puts the function it it, let alone calling it.

[phuah yun]

@KSSV im using R2018B. @bruno, thanks for your advises, but if youre not free to help its fine. Thanks.

[phuah yun]

 Vertices =load(''D:\Matlab\315 Big.txt');
 Vertices(:,1) = [] ;   % because all zeros     
 k=LineCurvature2D(Vertices) ; 
% This function calculates the curvature of a 2D line. It first fits 
% polygons to the points. Then calculates the analytical curvature from
% the polygons;
%
%  k = LineCurvature2D(Vertices,Lines)
% 
% inputs,
%   Vertices : A M x 2 list of line points.
%   (optional)
%   Lines : A N x 2 list of line pieces, by indices of the vertices
%         (if not set assume Lines=[1 2; 2 3 ; ... ; M-1 M])
%
% outputs,
%   k : M x 1 Curvature values
%
%
%
% Example, Circle
%  r=sort(rand(15,1))*2*pi;
%  Vertices=[sin(r) cos(r)]*10;
%  Lines=[(1:size(Vertices,1))' (2:size(Vertices,1)+1)']; Lines(end,2)=1;
%  k=LineCurvature2D(Vertices,Lines);
%
%  figure,  hold on;
%  N=LineNormals2D(Vertices,Lines);
%  k=k*100;
%  plot([Vertices(:,1) Vertices(:,1)+k.*N(:,1)]',[Vertices(:,2) Vertices(:,2)+k.*N(:,2)]','g');
%  plot([Vertices(Lines(:,1),1) Vertices(Lines(:,2),1)]',[Vertices(Lines(:,1),2) Vertices(Lines(:,2),2)]','b');
%  plot(sin(0:0.01:2*pi)*10,cos(0:0.01:2*pi)*10,'r.');
%  axis equal;
%
% Example, Hand
%  load('testdata');
%  k=LineCurvature2D(Vertices,Lines);
%
%  figure,  hold on;
%  N=LineNormals2D(Vertices,Lines);
%  k=k*100;
%  plot([Vertices(:,1) Vertices(:,1)+k.*N(:,1)]',[Vertices(:,2) Vertices(:,2)+k.*N(:,2)]','g');
%  plot([Vertices(Lines(:,1),1) Vertices(Lines(:,2),1)]',[Vertices(Lines(:,1),2) Vertices(Lines(:,2),2)]','b');
%  plot(Vertices(:,1),Vertices(:,2),'r.');
%  axis equal;
%
% Function is written by D.Kroon University of Twente (August 2011)

% If no line-indices, assume a x(1) connected with x(2), x(3) with x(4) ... if(nargin<2) Lines=[(1:(size(Vertices,1)-1))' (2:size(Vertices,1))']; end

% Get left and right neighbor of each points Na=zeros(size(Vertices,1),1); Nb=zeros(size(Vertices,1),1); Na(Lines(:,1))=Lines(:,2); Nb(Lines(:,2))=Lines(:,1);

% Check for end of line points, without a left or right neighbor checkNa=Na==0; checkNb=Nb==0; Naa=Na; Nbb=Nb; Naa(checkNa)=find(checkNa); Nbb(checkNb)=find(checkNb);

% If no left neighbor use two right neighbors, and the same for right... Na(checkNa)=Nbb(Nbb(checkNa)); Nb(checkNb)=Naa(Naa(checkNb));

% Correct for sampeling differences Ta=-sqrt(sum((Vertices-Vertices(Na,:)).^2,2)); Tb=sqrt(sum((Vertices-Vertices(Nb,:)).^2,2));

% If no left neighbor use two right neighbors, and the same for right... Ta(checkNa)=-Ta(checkNa); Tb(checkNb)=-Tb(checkNb);

% Fit a polygons to the vertices % x=a(3)*t^2 + a(2)*t + a(1) % y=b(3)*t^2 + b(2)*t + b(1) % we know the x,y of every vertice and set t=0 for the vertices, and % t=Ta for left vertices, and t=Tb for right vertices, x = [Vertices(Na,1) Vertices(:,1) Vertices(Nb,1)]; y = [Vertices(Na,2) Vertices(:,2) Vertices(Nb,2)]; M = [ones(size(Tb)) -Ta Ta.^2 ones(size(Tb)) zeros(size(Tb)) zeros(size(Tb)) ones(size(Tb)) -Tb Tb.^2]; invM=inverse3(M); a(:,1)=invM(:,1,1).*x(:,1)+invM(:,2,1).*x(:,2)+invM(:,3,1).*x(:,3); a(:,2)=invM(:,1,2).*x(:,1)+invM(:,2,2).*x(:,2)+invM(:,3,2).*x(:,3); a(:,3)=invM(:,1,3).*x(:,1)+invM(:,2,3).*x(:,2)+invM(:,3,3).*x(:,3); b(:,1)=invM(:,1,1).*y(:,1)+invM(:,2,1).*y(:,2)+invM(:,3,1).*y(:,3); b(:,2)=invM(:,1,2).*y(:,1)+invM(:,2,2).*y(:,2)+invM(:,3,2).*y(:,3); b(:,3)=invM(:,1,3).*y(:,1)+invM(:,2,3).*y(:,2)+invM(:,3,3).*y(:,3);

% Calculate the curvature from the fitted polygon k = 2*(a(:,2).*b(:,3)-a(:,3).*b(:,2)) ./ ((a(:,2).^2+b(:,2).^2).^(3/2));

function Minv = inverse3(M) % This function does inv(M) , but then for an array of 3x3 matrices adjM(:,1,1)= M(:,5).*M(:,9)-M(:,8).*M(:,6); adjM(:,1,2)= -(M(:,4).*M(:,9)-M(:,7).*M(:,6)); adjM(:,1,3)= M(:,4).*M(:,8)-M(:,7).*M(:,5); adjM(:,2,1)= -(M(:,2).*M(:,9)-M(:,8).*M(:,3)); adjM(:,2,2)= M(:,1).*M(:,9)-M(:,7).*M(:,3); adjM(:,2,3)= -(M(:,1).*M(:,8)-M(:,7).*M(:,2)); adjM(:,3,1)= M(:,2).*M(:,6)-M(:,5).*M(:,3); adjM(:,3,2)= -(M(:,1).*M(:,6)-M(:,4).*M(:,3)); adjM(:,3,3)= M(:,1).*M(:,5)-M(:,4).*M(:,2); detM=M(:,1).*M(:,5).*M(:,9)-M(:,1).*M(:,8).*M(:,6)-M(:,4).*M(:,2).*M(:,9)+M(:,4).*M(:,8).*M(:,3)+M(:,7).*M(:,2).*M(:,6)-M(:,7).*M(:,5).*M(:,3); Minv=bsxfun(@rdivide,adjM,detM);

[Bruno Luong]

• Remove function code in your script.
• But save function code in LineCurvature2D.m

[phuah yun]

Answer 1

[KSSV]

1. Download the function and save it in a folder
2. Copy your 315 Big.txt file in this folder.
3. Open MATLAB, go to the folder where you have saved the function and txt file.
4. Now type the following:

Vertices =load('315 Big.txt');
Vertices(:,1) = [] ;   % because all zeros     
k=LineCurvature2D(Vertices) ;
k

[phuah yun]

Hi KSSV, the values that i see now (k) are the curvatures?

[KSSV]

Jesus Christ.........you got it..yes those are the curvatures. :)

Now you have to accept the answer.

[phuah yun]

thank you so much~