How can I discretize a smooth curve?

If I have a smooth curve and I want to discretize this curve in some steps how can I do it? I saw some funtion in matlab but is does not work in my curve. See the image below.

[Lazaros Christoforidis]

so lets say you want to plot(x,y)

x,y are known matrices

try this:

for i=1:length(x)-1
    X(2*(i-1)+1)=x(i);
    Y(2*(i-1)+1)=y(i);
    
    X(2*i)=x(i);
    Y(2*i)=y(i+1);
end
plot(x,y,X,Y) % to see the difference

[KSSV]

If (x,y) is your data and you want to skip by a step

xi = x(1:step:end) ;
yi = y(1:step:end) ; 

[David Wilson]

Sample your curve at the required spacing, then use interp1 with the 'nearest' option.

[Tay]

Thank you all !! It really worked...I'm glad for the help !! :D

Possible to take internal values

Thanks again !!!

[ChrizzzlP]

You could just move the array of yvalues: y = y[2:end,end], may not be a pretty solution but it would work to get the internal values

[Lazaros Christoforidis]

for i=1:length(x)-1
    X(2*(i-1)+1)=x(i);
    Y(2*(i-1)+1)=y(i);
    
    X(2*i)=x(i+1);      %Change this 2 lines
    Y(2*i)=y(i);        %
end
plot(x,y,X,Y) % to see the difference

[Tay]

Lazaros Christoforidis, it is possible to change the step in your code? It is discretized very well, thank you. And now I'm getting the internal values !!! :))

I was wondering if I want to change the number of steps should I change the multiplyers in your code? There are too many steps and I can see if I zoom in the graph XD...

Thanks anyway

[Lazaros Christoforidis]

np, you could rescale your x, y values

[Stephen23]

https://web.archive.org/web/20211124063238/https://www.mathworks.com/matlabcentral/answers/523679-how-can-i-discretize-a-smooth-curve

Answer 1

[Cris LaPierre]

Try using the discretize function

y=linspace(3.5,3.4965);
x=linspace(0,1000);

plot(x,y)

% discretize
[Y,E] = discretize(y,20);

hold on
plot(x,E(Y),'--r')
hold off

Also, consider looking into the stairstep graph, though that seems to put the steps outside the curve again.

[Tay]

Thank you, Cris !! Now I can change my steps :))

Cris, it is possible to save the discrezed curve in a file txt?

[Lazaros Christoforidis]

M(:,1)=x; M(:,2)=y;
writematrix(M,'FileName.txt')

[Cris LaPierre]

I'm partial to tables, so I would recommend writetable:

% assume you have the previous code creating the necessary variables
ySteps = Y(E);

data = table(x,ySteps);
writetable(data,'filename.txt');

You can change the file extension to get different types of files.

• .txt, .dat, or .csv for delimited text files
• .xls, .xlsm, or .xlsx for Excel® spreadsheet files
• .xlsb for Excel spreadsheet files supported on systems with Excel for Windows®

[Lazaros Christoforidis]

yeah thats smooth

[Tay]

Thanks guys !! It's perfectly working !! :D :)