圆柱体

1.绘制圆柱体，计算圆柱体表面某一点的法向量。

 1 r=5;
 2 h=10;
 3 n=100;%分点数
 4 radius = 1.0;%搜索半径
 5 min_neighbors = 8;
 6 %-------------------------------
 7 n_h= floor(h/(r*2*pi/n));
 8 X=zeros(n,n_h);
 9 Y=zeros(n,n_h);
10 Z=zeros(n,n_h);
11 for j=1:n_h
12 for i=1:n
13     X(i,j)=r*cos(i*2*pi/n);
14     Y(i,j)=r*sin(i*2*pi/n);
15     Z(i,j)=j*r*2*pi/n;
16 end
17 end
18 
19 data=zeros(n*n_h,3);
20 data(:,1)=reshape(X,[n*n_h,1]);
21 data(:,2)=reshape(Y,[n*n_h,1]);
22 data(:,3)=reshape(Z,[n*n_h,1]);
23 tree=KDTreeSearcher(data);
24 query=[X(50,20),Y(50,20),Z(50,20)];
25 hold on
26 plot3(X,Y,Z,'r.','MarkerSize',1)
27 plot3(query(:,1),query(:,2),query(:,3),'b.','MarkerSize',4)
28 idx = rangesearch(tree, query, radius);                                                  
29 idxs = idx{1};
30 neighbors = [data(idxs(:),1) data(idxs(:),2) data(idxs(:),3)];
31 if size(neighbors) < min_neighbors
32     normal = {1};
33     return;
34 end
35 C = cov(neighbors);% 计算协方差矩阵
36 [v, lambda] = eig(C);
37 [~, i_min] = min(diag(lambda));
38 [~, i_max] = max(diag(lambda));
39 normal = v(:,i_min) ./ norm(v(:,i_min));
40 normal_max = v(:,i_max) ./ norm(v(:,i_max));
41 query1=[normal(1,1)+ query(1,1),normal(2,1)+ query(1,2),normal(3,1)+ query(1,3)];
42 query2=[normal_max(1,1)+ query(1,1),normal_max(2,1)+ query(1,2),normal_max(3,1)+ query(1,3)];
43 plot3([query1(1,1) query(1,1)],[query1(1,2) query(1,2)],[query1(1,3) query(1,3)],'LineWidth',1);
44 plot3([query2(1,1) query(1,1)],[query2(1,2) query(1,2)],[query2(1,3) query(1,3)],'LineWidth',1);
45 
46 
47 hold off
48 axis equal