Fitting spline to outline

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John Fullerton
John Fullerton 2019-8-7
评论： Mehri Mehrnia 2022-6-20
I have been trying to write a code (shown below) that will identify the outline of an object and then fit a spline to it.
I can identify the edge (using a ball for example below, image 1), but it picks up multiple points around the edge for each x and y value (image 2). So, I've tried to clean it up be removing some of the points.
However, the final spline doubles back on itself (image 4). How do I stop that from happening and just plot a smooth line connecting all the points?
% Get outline
BW = edge(Image, 'Canny', 0.6);
B = bwboundaries(BW);
J = num2cell(cell2mat(B),1);
F(:,1) = J{1,1};
F(:,2) = J{1,2};
%Show image and outline points
figure
imshow(I)
hold on
scatter(F(:,1),F(:,2), 'r0')
%Reduce number of points
for q = 20:20:(numel(F)/2)
F1((q/20),:) = F(q,:);
end
% Fit spline
x = F1(:,1);
y = F1(:,2);
pointspline = [x'; y'];
values = cscvn(pointspline);
sp = fn2fm(values,'B-')
%Show reduced points and spline
figure
scatter(F1(:,1),F1(:,2), 'r')
hold on
fnplt(sp)
1.
Sphere_Edge.png
2.
Sphere_Edge_Close.png
3.
Ball_Spline.png
4.
Spline_Close.png
  2 个评论
darova
darova 2019-8-8
If the curve double back can you just use a half of data?
%Reduce number of points
% for q = 20:20:(numel(F)/2)
% F1((q/20),:) = F(q,:);
% end
% can be written as:
F1 = F(1:20:end/2,:);
Mehri Mehrnia
Mehri Mehrnia 2022-6-20
something is wrong with this code, I used it for a boundary of image. it shifts it 90 degrees.

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回答（1 个）

Pujitha Narra
Pujitha Narra 2019-8-19
Hi John,
There is a similar example here:
https://in.mathworks.com/help/images/boundary-tracing-in-images.html
Hope this helps.

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