Finding intersection point for polygon with hole

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Kayra Dernek
Kayra Dernek 2022-3-30
评论： Matt J 2022-3-30
I am trying to find intersection points of polygons with holes and lines. However linexlines2d function finds in an unexpected intersection point in x=0.1, y = 0.1 as seen in the figure. Is there a way to prevent this. By the way I am trying to find intersection points so that I can discretisize the boundry with additional nodes with linspace function. Then I will use delauneyTriangulation to mesh the surface. So my main goal is to be able to mesh any polygon. I would really appreciate any other recomendation to achive this result.
Thanks
clc
clear
clf
polyOut=polyshape([0 0; 1 0; 0 1]); %Create triangular polyshape with hole
polyIn=polyOut.scale(0.5,[1/3,1/3]);
poly=polyOut.subtract(polyIn);
plot(poly)
hold on
for i=0:0.1:1
[x1,y1,x2,y2]=deal(-1,i,2,i); %line from (0,0) to (1,1)
out=linexlines2D(poly,[x1,y1],[x2,y2]);
%Visualize
col=[0.6400 0.0800 0.1800];
plot([x1,x2],[y1,y2],'--','Color',col);
plot(out(1,:),out(2,:),'o','MarkerFaceColor','r');
end
  2 个评论
Torsten
Torsten 2022-3-30
编辑：Torsten 2022-3-30
@Kayra Dernek
If the aim is to create a boundary mesh, why don't you use the parametric form of the boundary to create points on it ?
E.g. a circle is given by (R*cos(t),R*sin(t)) for 0<=t<2*pi.
Now just use
R = 1;
f = @(t) [R*cos(t);R*sin(t)];
t = linspace(0,2*pi,10);
S = f(t);
plot (S(1,:),S(2,:))
Matt J
Matt J 2022-3-30
However linexlines2d function finds in an unexpected intersection point in x=0.1, y = 0.1 as seen in the figure.
A debugged version of the File Exchange file linexlines2D has now been uploaded.

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回答（1 个）

Matt J
Matt J 2022-3-30
编辑：Matt J 2022-3-30
Ran in:
By the way I am trying to find intersection points so that I can discretisize the boundry with additional nodes with linspace function
Here's an easier way to add more edge samples:
polyOut=polyshape([0 0; 1 0; 0 1]); %Create triangular polyshape with hole
polyIn=polyOut.scale(0.5,[1/3,1/3]);
V=[morepoints(polyOut,15);morepoints(polyIn,10)];
plot(V(:,1),V(:,2),'or','MarkerFace','r'); axis equal; axis padded
hold on; plot(subtract(polyOut,polyIn),'FaceColor','b') ; hold off
function V=morepoints(poly,N)
%Create a list of points along polyshape edges, N per side.
t=linspace(0,1,N)'; t(end)=[];
V=poly.Vertices;
V=kron(V,t)+kron(V([2:end,1],:), 1-t);
end

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