facing a PointLocation error while using ginput !

Hello! HELP PLEASE! I am using the PointLocation in my script but I keep getting this error 'Undefined function 'PointLocation' for input arguments of type double', knowing that the input is a point coordinates (x,y) obtained using 'ginput' function and a delaunay triangulation (DT) such that: T= PointLocation ( DT, x,y)

[Walter Roberson]

Are you creating the variable in one function and trying to use it in another function?

[Ano]

No, all in the same script. The only input whose type is double is the delaunay triangulation, could it be the source of the problem, if so any suggestions ?! thanks

[Adam]

What is PointLocation? You haven't filled in anything in the 'Products' box, but I don't see this function in base Matlab.

[Ano]

Yes, in my code it is with lower p but even though I still get the error !!

[Walter Roberson]

Please show how you construct DT and call pointLocation

Answer 1

[Walter Roberson]

Lowercase p

See the older https://www.mathworks.com/help/matlab/ref/delaunaytri.pointlocation.html and the newer https://www.mathworks.com/help/matlab/ref/triangulation.pointlocation.html

[Walter Roberson]

You have gotten confused between delaunay() and delaunayTriangulation() . The one you are using produces a numeric matrix, which cannot be used with pointPosition .

[Ano]

well it did prevent the error from appearing.Thank you ! Best regards!

[ABDUL REHMAN]

Dear Ano, How you get rid of the error.? 'Undefined function 'PointLocation' for input arguments of type double' I am getting same error. kindly suggest me a way.

Thanks

[Walter Roberson]

See my answer about the using delaunayTriangulation as the function name.

[ABDUL REHMAN]

Thanks, I have changed it to delaunayTriangulation. TRI = delaunayTriangulation(X,Y);

The error now saying

"Error using delaunayTriangulation
The input points must be specified in column-vector format."

I have changed it again to

TRI = delaunayTriangulation([X',Y']);

Now the error shifted to next line saying

"Error using delaunayTriangulation/subsasgn
Invalid arguments in indexing operation."

Error in...
"t(4,:)=0;"

This is the code.

TRI = delaunayTriangulation([X',Y']);
t=TRI';
t(4,:)=0;

[Walter Roberson]

The TRI returned from delaunayTriangulation is an object . You cannot index all columns of an object.

I am not sure what you are trying to do with that statement.

[ABDUL REHMAN]

Thanks, Actually I want to create mesh structure using delaunayTriangulation and then pick some triangles using graphical input, "ginput". When i used just "delaunay" it gives me indexing array. but when i use delaunayTriangulation it gives me object, which can't be used as an indexing operation.

[Walter Roberson]

ginput returns coordinates. Pass those as the second argument to pointLocation. The second output is the coordinates of the vertices if you need coordinates. The first output is the triangle ID. If for some reason the coordinates are not enough and you need to index by the triangle ID then use the CoordinatePositions method of the triangulation.

[ABDUL REHMAN]

Thnaks again for your help, I m posting here my code, still getting error.

h=0.01;
L=0.10;   
W=0.05;    
Nx=17;    
Ny=9;      

Number=3;

epsilon=1e-6;
M=1;
for i=1:Nx+1
    for j=1:Ny+1
        X(M)=-L/2+(i-1)/Nx*L;
        Y(M)=-W/2+(j-1)/Ny*W-epsilon*X(M);
        M=M+1;
    end
end

TRI = delaunayTriangulation([X',Y']);
t=TRI';
t(4,:)=0;
p=[X; Y; -h*ones(1,length(X))];
save plate p t

PatchNumber=[];
viewer plate; view(0,90); hold on
m=0;
while ~isempty(t)
    m=m+1;
    [xi,yi]=ginput;

      TriangleNumber = pointLocation(TRI,xi,yi);
      n=t(1:3,TriangleNumber);
      PatchNumber= [PatchNumber TriangleNumber];
      x= p(1,n);
      y= p(2,n);
      if isempty(xi|yi) break; end
      fill(x,y,Color4)
      clear xi yi
  end
  t(4,:)=3;
  t(4,PatchNumber)=2;
  save plate p t

with the delaunayTriangulation, the error is what I mentioned above.

"Error using delaunayTriangulation/subsasgn
Invalid arguments in indexing operation."
Error in...
"t(4,:)=0;"

When I use just delaunay it runs but gives error at pointLocation when I pick the points using ginput, with the input type double.

[Walter Roberson]

It is meaningless to set the 4th column of a triangulation object.

Answer 2

[Ano]

the DT was constructed as it follow:

    N=20;     %Discretization parameter 
    L=50;     % Length 
    for i=1:N+1 %descritisation
        for j=1:N+1
            X(i)=-L/2+(i-1)/N*L;
            Y(j)=-L/2+(j-1)/N*L;
        end
    end
    DT = delaunay(X,Y);
    DTt=DT';
    while ~isempty(DTt)
        [x,y]=ginput(1);
        T = pointLocation ( DT, x ,y);
    end