how to get one shape out of multiple shapes
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Asliddin Komilov
am 13 Dez. 2023
Kommentiert: Asliddin Komilov
am 22 Dez. 2023
Hi,
I have multiple shapes I need to merge into a single shape, because I have sets of shapes those I have to merge and compare with each other (put into a one plot).
the set of data is attached and I can plot it like this:
plot(X(:, [1:end 1])', Y(:, [1:end 1])')
let me know, if you know how to do it, thanks.
I got this shape using patch, but it generated a Patch file that I cannot use.
Ideally, I would like my data was interpolated so the final shape will not have sharp edges but be smooth and go down to Y=0.
Help me handle that too if you can. thanks
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1567734/image.png)
1 Kommentar
Dyuman Joshi
am 13 Dez. 2023
"I got this shape using patch, but it generated a Patch file that I cannot use."
You can't use the patch object or you can't use the output generated?
What is the expected output? It will be helpful if you can show an illustration.
Akzeptierte Antwort
DGM
am 13 Dez. 2023
patch() doesn't create a file. If you created a file somehow, nobody knows how you did it.
I'm not sure where this is going, but here's a guess.
% loads X,Y
load data.mat
% get rid of NaNs
xhasnans = any(isnan(X),2);
yhasnans = any(isnan(Y),2);
goodrows = ~(xhasnans | yhasnans);
X = X(goodrows,:);
Y = Y(goodrows,:);
% find convex hull
K = convhull(double(X),double(Y));
Xh = X(K);
Yh = Y(K);
% plot the convex hull, show the curve endpoint
plot(Xh,Yh); hold on
plot(X(1),Yh(1),'o')
% get rid of the base of the curve
Xh = Xh(3:end-1);
Yh = Yh(3:end-1);
% extrapolate to Y=0 from last 10 datapoints
Np = 10; % number of points to use
% the right-hand part of the curve
Yhr = Yh(1:Np);
Xhr = Xh(1:Np);
Yexr = [0;Yhr];
Xexr = interp1(Yhr,Xhr,Yexr,'linear','extrap');
% the left-hand part of the curve
Yhl = Yh(end-Np+1:end);
Xhl = Xh(end-Np+1:end);
Yexl = [Yhl;0];
Xexl = interp1(Yhl,Xhl,Yexl,'linear','extrap');
% put them back together
Xex = [Xexr; Xh(Np+1:end-Np); Xexl];
Yex = [Yexr; Yh(Np+1:end-Np); Yexl];
% close the curve (if needed
Xex = Xex([1:end 1]);
Yex = Yex([1:end 1]);
% plot the extraploated curve, show the endpoint
plot(Xex,Yex,'--')
plot(Xex(1),Yex(1),'*')
3 Kommentare
DGM
am 14 Dez. 2023
I wouldn't call it a guess. I picked it manually based on the given hull. For a different set of polygons, I don't know that it would be consistently correct.
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Mathieu NOE
am 13 Dez. 2023
hello
try this
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1568324/image.png)
x = double(X(:));
y = double(Y(:));
% remove nan
id = isnan(x) & isnan(y);
x(id) = [];
y(id) = [];
% k = boundary(___,s) specifies shrink factor s using any of the previous syntaxes.
% s is a scalar between 0 and 1. Setting s to 0 gives the convex hull,
% and setting s to 1 gives a compact boundary that envelops the points.
% The default shrink factor is 0.5.
s = 0.1;
k = boundary(x,y,s);
x_out = x(k);
y_out = y(k);
% find lower left "corner" point to make extrapolation towards Y = 0
[mx,ix1] = min(x_out);
my = y_out(ix1);
ind = find(x_out<(mx+1));
slope = mean(diff(y_out(ind))./diff(x_out(ind)));
x_lower_left = mx - my/slope;
% find lower right "corner" point to make extrapolation towards Y = 0
[mx,ix2] = max(x_out);
my = y_out(ix2);
ind = find(x_out>(mx-1));
slope = mean(diff(y_out(ind))./diff(x_out(ind)));
x_lower_right = mx - my/slope;
% add those two new points to x_out and y_out
x_out2 = [x_out(1:ix2-1); x_lower_right; x_out(ix2:ix1); x_lower_left; x_out(ix1+1:end) ] ;
y_out2 = [y_out(1:ix2-1); 0 ; y_out(ix2:ix1); 0 ; y_out(ix1+1:end) ] ;
plot(x,y, '*', x_out, y_out, '-*r', x_out2, y_out2, '-g')
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