我有一系列的矩形,知道它们各自4个角的确切位置。我想绘制它们并通过它们中的每一个来创建类似于矩形横截面的3D管道。这些点也不应限于遵循直轴。它应该灵活地采取偏差。我还希望两个端点被修补关闭。
我在你的网站上看到了一个类似的问题:“如何用椭圆形放置在MATLAB或Python中创建一个3d空心管道?”。答案给我留下了深刻的印象,但对于省略号和圆圈来说却很遗憾。我试图让它与矩形一起工作,但无法弄清楚所需的逻辑。我也尝试将所有东西拼凑起来,但这导致产生锋利的边缘,这是我不想要的。我的代码看起来像这样:
A = importdata(filename);
[size_A, ~] = size(A.data);
axis vis3d;
for i=1:12:size_A-12
X1 = A.data(i+1); X2 = A.data(i+4); X3 = A.data (i+7); X4= A.data (i+10);
Y1 = A.data(i+2); Y2 = A.data(i+5); Y3 = A.data(i+8); Y4 = A.data(i+11);
Z1 = A.data(i+3); Z2 = A.data(i+6); Z3 = A.data(i+9); Z4 = A.data(i+12);
X= [X1;X2;X3;X4];
Y= [Y1;Y2;Y3;Y4];
Z= [Z1;Z2;Z3;Z4];
plot3(X, Y, Z)
patch(X, Y, Z, 'g'); %% for the particular planes
if(i>1) %% for the patching between two planes
A1= [ X1 X1 X2 X4; a1 X4 a2 X3; a2 a4 a3 a3; X2 a1 X3 a4];
B1= [ Y1 Y1 Y2 Y4; b1 Y4 b2 Y3; b2 b4 b3 b3; Y2 b1 Y3 b4];
C1= [ Z1 Z1 Z2 Z4; c1 Z4 c2 Z3; c2 c4 c3 c3; Z2 c1 Z3 c4];
plot3(A1, B1, C1)
patch(A1, B1, C1, 'g');
end
a1=X1; a2=X2; a3=X3; a4=X4;
b1=Y1; b2=Y2; b3=Y3; b4=Y4;
c1=Z1; c2=Z2; c3=Z3; c4=Z4;
figure(1)
grid on
axis equal
hold on
xlabel('x');
ylabel('y');
zlabel('z');
end
最终结果应该像一个非常弯曲的管道,矩形横截面。不应该有任何尖角。
PS:MATLAB文件正在导入记事本.txt文档,其中坐标输入如下所示 -
Number_of_sections= 7
X_coordinate= 60.00
Y_coordinate= 13.00
Z_coordinate= -7.50
X_coordinate= 60.00
Y_coordinate= -13.00
Z_coordinate= -7.50
X_coordinate= 60.00
Y_coordinate= -13.00
Z_coordinate= -12.50
X_coordinate= 60.00
Y_coordinate= 13.00
Z_coordinate= -12.50
X_coordinate= 95.00
Y_coordinate= 13.00
Z_coordinate= -7.50
X_coordinate= 95.00
Y_coordinate= -13.00
Z_coordinate= -7.50
X_coordinate= 95.00
Y_coordinate= -13.00
Z_coordinate= -12.50
X_coordinate= 95.00
Y_coordinate= 13.00
Z_coordinate= -12.50
X_coordinate= 95.50
Y_coordinate= 13.50
Z_coordinate= -7.50
X_coordinate= 95.50
Y_coordinate= -13.50
Z_coordinate= -7.50
X_coordinate= 95.50
Y_coordinate= -13.50
Z_coordinate= -12.50
X_coordinate= 95.50
Y_coordinate= 13.50
Z_coordinate= -12.50
X_coordinate= 96.00
Y_coordinate= 14.00
Z_coordinate= -7.50
X_coordinate= 96.00
Y_coordinate= -14.00
Z_coordinate= -7.50
X_coordinate= 96.00
Y_coordinate= -14.00
Z_coordinate= -12.50
X_coordinate= 96.00
Y_coordinate= 14.00
Z_coordinate= -12.50
X_coordinate= 96.50
Y_coordinate= 14.50
Z_coordinate= -7.50
X_coordinate= 96.50
Y_coordinate= -14.50
Z_coordinate= -7.50
X_coordinate= 96.50
Y_coordinate= -14.50
Z_coordinate= -12.50
X_coordinate= 96.50
Y_coordinate= 14.50
Z_coordinate= -12.50
X_coordinate= 97.00
Y_coordinate= 15.00
Z_coordinate= -7.50
X_coordinate= 97.00
Y_coordinate= -15.00
Z_coordinate= -7.50
X_coordinate= 97.00
Y_coordinate= -15.00
Z_coordinate= -12.50
X_coordinate= 97.00
Y_coordinate= 15.00
Z_coordinate= -12.50
X_coordinate= 99.00
Y_coordinate= 15.00
Z_coordinate= -7.50
X_coordinate= 99.00
Y_coordinate= -15.00
Z_coordinate= -7.50
X_coordinate= 99.00
Y_coordinate= -15.00
Z_coordinate= -12.50
X_coordinate= 99.00
Y_coordinate= 15.00
Z_coordinate= -12.50
X_coordinate= 99.250
Y_coordinate= 14.7500
Z_coordinate= -7.50
X_coordinate= 99.250
Y_coordinate= -15.2500
Z_coordinate= -7.50
X_coordinate= 99.250
Y_coordinate= -15.2500
Z_coordinate= -12.50
X_coordinate= 99.250
Y_coordinate= 14.7500
Z_coordinate= -12.50
X_coordinate= 99.50
Y_coordinate= 14.50
Z_coordinate= -7.50
X_coordinate= 99.50
Y_coordinate= -15.500
Z_coordinate= -7.50
X_coordinate= 99.50
Y_coordinate= -15.500
Z_coordinate= -12.50
X_coordinate= 99.50
Y_coordinate= 14.50
Z_coordinate= -12.50
X_coordinate= 100.0
Y_coordinate= 14.00
Z_coordinate= -7.50
X_coordinate= 100.0
Y_coordinate= -15.750
Z_coordinate= -7.50
X_coordinate= 100.0
Y_coordinate= -15.750
Z_coordinate= -12.50
X_coordinate= 100.0
Y_coordinate= 14.00
Z_coordinate= -12.50
X_coordinate= 110.0
Y_coordinate= 14.00
Z_coordinate= -7.50
X_coordinate= 110.0
Y_coordinate= -15.750
Z_coordinate= -7.50
X_coordinate= 110.0
Y_coordinate= -15.750
Z_coordinate= -12.50
X_coordinate= 110.0
Y_coordinate= 14.00
Z_coordinate= -12.50
X_coordinate= 110.0
Y_coordinate= 14.00
Z_coordinate= -7.50
X_coordinate= 110.0
Y_coordinate= -15.750
Z_coordinate= -7.50
X_coordinate= 120.0
Y_coordinate= -15.750
Z_coordinate= -12.50
X_coordinate= 120.0
Y_coordinate= 14.00
Z_coordinate= -12.50
X_coordinate= 110.0
Y_coordinate= 14.00
Z_coordinate= -5.50
X_coordinate= 110.0
Y_coordinate= -15.750
Z_coordinate= -5.50
X_coordinate= 120.0
Y_coordinate= -15.750
Z_coordinate= -7.50
X_coordinate= 120.0
Y_coordinate= 14.00
Z_coordinate= -7.50
X_coordinate= 80.0
Y_coordinate= 14.00
Z_coordinate= -5.50
X_coordinate= 80.0
Y_coordinate= -15.750
Z_coordinate= -5.50
X_coordinate= 80.0
Y_coordinate= -15.750
Z_coordinate= -7.50
X_coordinate= 80.0
Y_coordinate= 14.00
Z_coordinate= -7.50
X_coordinate= 70.0
Y_coordinate= 14.00
Z_coordinate= -5.50
X_coordinate= 70.0
Y_coordinate= -15.750
Z_coordinate= -5.50
X_coordinate= 80.0
Y_coordinate= -15.750
Z_coordinate= -5.50
X_coordinate= 80.0
Y_coordinate= 14.00
Z_coordinate= -5.50
X_coordinate= 70.0
Y_coordinate= 14.00
Z_coordinate= -2.50
X_coordinate= 70.0
Y_coordinate= -15.750
Z_coordinate= -2.50
X_coordinate= 80.0
Y_coordinate= -15.750
Z_coordinate= -2.50
X_coordinate= 80.0
Y_coordinate= 14.00
Z_coordinate= -2.50
期望的方向变化图2
图3中方向所需变化的更详细表示
这个答案最初发布在我的第一个答案中,但第一个答案太拥挤,难以追踪。因此,我现在将这个答案分开给第二个答案。这也是解决问题的另一种不同方法。
如果你有一组具有良好密度的点,你可以使用MATLAB的内置插值函数interp1
。
首先,您需要参数化点。和弦长度在这里足够好:
clear
filename = 'datafile.txt';
A = importdata(filename);
vertices = A.data(2:end);
vertices = reshape(vertices, 12, [])';
for i = 1:4
% take a set of vertices that will form an edge of the lofted body.
ishift = (i-1) * 3 + 1;
p = vertices(:,ishift:ishift+2);
%calculate distance between two neighbouring points.
dp = sqrt(sum(diff(p).^2,2));
u = [0; cumsum(dp)/sum(dp)];
% do more later
end
然后生成一组新的u值来计算拟合点:
unew = unique([u; linspace(0,1,500)']);
然后与interp1
交换点:
pnew = interp1(u, p, unew, 'spline');
figure; hold on;
plot3(pnew(:,1), pnew(:,2), pnew(:,3));
plot3(p(:,1), p(:,2), p(:,3),'o');
axis equal;
总结一下for
循环现在是:
for i = 1:4
ishift = (i-1) * 3 + 1;
p = vertices(:,ishift:ishift+2);
dp = sqrt(sum(diff(p).^2,2));
u = [0; cumsum(dp)/sum(dp)];
unew = unique([u; linspace(0,1,500)']);
pnew = interp1(u, p, unew, 'spline');
x(:,i) = pnew(:,1);
y(:,i) = pnew(:,2);
z(:,i) = pnew(:,3);
end
但是,由于每条边只有10个点,因此您将获得如下结果:
采取其中一条边缘曲线:
V1和V2之间的巨大曲率显然是不可取的。但是,由于V1和V2之间的变化只需要是线性的,因此可以人为地在它们之间添加点。例如,添加两点:
p = vertices(:,ishift:ishift+2);
insertedP = (p(2,:) - p(1,:)).*(0.33; 0.66);
insertedP = insertedP + repmat(p(1,:),size(insertedP,1),1);
p = [p(1,:); insertedP; p(2:end,:)];
然后进行相同的计算,得到:
如果你添加更多:
insertedP = (p(2,:) - p(1,:)).*(0.02:0.02:0.98)';
但它并不完美,因为你会在V2处获得可见的振荡,这是不可避免的因为连续性:
但是,可以通过删除或添加接近V2的点来控制它:
insertedP = (p(2,:) - p(1,:)).*(0.02:0.02:0.68)';
请注意,您也可以使用另一个答案中公布的B样条方法获得此类振荡,但通过将第二个控制点移近或更接近V2,它更易于控制和预测。
使用interp1
方法生成的放样体如下:
总而言之,下面给出了重现上述图像的完整代码:
clear
filename = 'datafile.txt';
A = importdata(filename);
vertices = A.data(2:end);
vertices = reshape(vertices, 12, [])';
for i = 1:4
ishift = (i-1) * 3 + 1;
p = vertices(:,ishift:ishift+2);
insertedP = (p(2,:) - p(1,:)).*(0.02:0.02:0.98)';
insertedP = insertedP + repmat(p(1,:),size(insertedP,1),1);
p = [p(1,:); insertedP; p(2:end,:)];
dp = sqrt(sum(diff(p).^2,2));
u = [0; cumsum(dp)/sum(dp)];
unew = unique([u; linspace(0,1,500)']);
pnew = interp1(u, p, unew, 'spline');
x(:,i) = pnew(:,1);
y(:,i) = pnew(:,2);
z(:,i) = pnew(:,3);
end
c = repmat(1:numel(x)/4,4,1)';
xx=[x;flipud(x(:,[2,3,4,1]))];
yy=[y;flipud(y(:,[2,3,4,1]))];
zz=[z;flipud(z(:,[2,3,4,1]))];
cc=[c;flipud(c)];
figure; patch(xx,yy,zz,cc);
如果你有更多的点来约束插值,你可以删除涉及insertP
的行:
insertedP = (p(2,:) - p(1,:)).*(0.02:0.02:0.98)';
insertedP = insertedP + repmat(p(1,:),size(insertedP,1),1);
p = [p(1,:); insertedP; p(2:end,:)];
通过数据文件中的点插值无法轻松完成。我建议设计B样条曲线来插值平面1和2以及平面6和7之间的点。平面2和平面6,平面7和平面10之间的空间看起来非常线性:
clear
filename = 'datafile.txt';
A = importdata(filename);
vertices = A.data(2:end);
vertices = reshape(vertices, 12, [])';
vx = vertices(:, 1:3:10);
vy = vertices(:,2:3:11);
vz = vertices(:,3:3:12);
figure; patch(vx',vy',vz',1); axis equal;
没有简单的方法来进行这种插值,因为您希望确保沿曲线至少保持C1连续性以避免任何尖锐边缘。 B样条曲线在这里很有用,但是如果你不熟悉它,你将很难编程。幸运的是,我参与了一个需要曲面和曲线拟合的项目,我手头有代码:
function [x,y,z] = bspline(u, ctrlp, k, knots)
U = bspbasis(u, numel(ctrlp(:,1)), k, knots);
x=U*ctrlp(:,1);
y=U*ctrlp(:,2);
z=U*ctrlp(:,3);
end
function U = bspbasis(u, nctrlp, K, knots)
nu = numel(u);
umax = max(u);
index = 1:nctrlp;
% preallocating variables
U = zeros(nu,nctrlp);
N = zeros(nctrlp+1,K);
% Calculate the denominators for basis functions (k>2). -may be useful when
% the size of point data is substantial, so the calculation is not repeated.
d1 = zeros(nctrlp,K);
d2 = d1;
for m=2:K
d1(:,m) = knots(index+m-1) - knots(index);
d2(:,m) = knots(index+m) - knots(index+1);
end
knots = knots(:);
knots1 = knots(1:nctrlp+1);
knots2 = knots(2:nctrlp+2);
knotSize = size(knots1);
knotc1 = knots(nctrlp+1);
knotc2 = knots(nctrlp+2);
for ui = 1:nu
% k = 1
u_ = u(ui)*ones(knotSize);
NA = u_>=knots1 & u_<knots2;
if u(ui) == umax && knotc1 == umax && knotc2 == umax
NA(1:nctrlp+1) = 0;
NA(end-1,1) = 1;
end
N(:,1) = NA;
% k > 2
for k = 2:K
p1 = (u(ui) - knots(index)) ./ d1(:,k) .* N(index,k-1);
p1(isnan(p1)) = 0;
p2 = (knots(index+k) - u(ui)) ./ d2(:,k) .* N(index+1,k-1);
p2(isnan(p2)) = 0;
N(index,k) = p1 + p2;
end
U(ui,:)=N(1:end-1,k);
end
end
如果您想了解上述代码,可以阅读B-spline Wikipedia。 Youtube上还有许多教程和this one等互动工具。
下面的代码将三阶B样条拟合到四组角顶点中的每一个。
u = linspace(0,1,500);
k = 3;
for i = 1:4
ishift = (i-1) * 3 + 1;
p = vertices(:,ishift:ishift+2);
ctrlp = [p(1,:); [0 0 0]; p(2:3,:); p(5:6,:); zeros(2,3); p(7,:); p(8,:)];
ctrlp(2,:) = 5*ctrlp(3,:) - 4*ctrlp(4,:);
ctrlp(7,:) = 2*ctrlp(6,:) - ctrlp(5,:);
ctrlp(8,:) = 4*ctrlp(9,:) - 3*ctrlp(10,:);
knots = getknots(ctrlp, k);
[x_,y_,z_] = bspline(u, ctrlp, k, knots);
x(:,i) = [p(:,1); x_];
y(:,i) = [p(:,2); y_];
z(:,i) = [p(:,3); z_];
[~,I] = sort(x(:,i));
x(:,i) = x(I,i);
y(:,i) = y(I,i);
z(:,i) = z(I,i);
end
c = repmat(1:numel(x)/4,4,1)';
xx=[x;flipud(x(:,[2,3,4,1]))];
yy=[y;flipud(y(:,[2,3,4,1]))];
zz=[z;flipud(z(:,[2,3,4,1]))];
cc=[c;flipud(c)];
figure; patch(xx,yy,zz,cc);
结果是平滑的放样表面:
我想向你解释代码是如何工作的,但是在我努力了一个小时之后,我放弃了......相反,我提供了以下一些关键点的摘要。
在摘要中,使用以下符号:C1,C2,...,C10是B样条曲线的控制点,V1,V2,...,V10是用于计算B样条曲线的顶点。下图显示了用于计算第一个B样条曲线的控制点和顶点。
u
中的值的数量决定了最终曲线上的点数。C1 = V1
和C10 = V10
。C2 - V2 = d*(V2-V3)
和C3 = V2
。C3 = V2; C4 = V3; C5 = V5; C6 = V6
。C7-V6 = d*(V6-V5)
。C8-V7 = d*(V7-V8); C9 = V7;
。C10 = V10
和C9 = V7
开始,曲线经过V8和V9。getknots
getknots
功能:
function knots = getknots(ctrlp, k)
d = sqrt(sum(diff(ctrlp).^2, 2));
ds = cumsum(d)./sum(d);
knots = [zeros(k,1); ds(k-1:end); ones(k,1)];
end
bspline
方法的所有代码:
clear
filename = 'datafile.txt';
A = importdata(filename);
vertices = A.data(2:end);
vertices = reshape(vertices, 12, [])';
u = linspace(0,1,500);
k = 3;
for i = 1:4
ishift = (i-1) * 3 + 1;
p = vertices(:,ishift:ishift+2);
ctrlp = [p(1,:); [0 0 0]; p(2:3,:); p(5:6,:); zeros(2,3); p(7,:); p(8,:)];
ctrlp(2,:) = 5*ctrlp(3,:) - 4*ctrlp(4,:);
ctrlp(7,:) = 2*ctrlp(6,:) - ctrlp(5,:);
ctrlp(8,:) = 4*ctrlp(9,:) - 3*ctrlp(10,:);
knots = getknots(ctrlp, k);
[x_,y_,z_] = bspline(u, ctrlp, k, knots);
x(:,i) = [p(:,1); x_];
y(:,i) = [p(:,2); y_];
z(:,i) = [p(:,3); z_];
[~,I] = sort(x(:,i));
x(:,i) = x(I,i);
y(:,i) = y(I,i);
z(:,i) = z(I,i);
end
c = repmat(1:numel(x)/4,4,1)';
xx=[x;flipud(x(:,[2,3,4,1]))];
yy=[y;flipud(y(:,[2,3,4,1]))];
zz=[z;flipud(z(:,[2,3,4,1]))];
cc=[c;flipud(c)];
figure; patch(xx,yy,zz,cc);
function [x,y,z] = bspline(u, ctrlp, k, knots)
U = bspbasis(u, numel(ctrlp(:,1)), k, knots);
x=U*ctrlp(:,1);
y=U*ctrlp(:,2);
z=U*ctrlp(:,3);
end
function U = bspbasis(u, nctrlp, K, knots)
nu = numel(u);
umax = max(u);
index = 1:nctrlp;
% preallocating variables
U = zeros(nu,nctrlp);
N = zeros(nctrlp+1,K);
% Calculate the denominators for basis functions (k>2). -may be useful when
% the size of point data is substantial, so the calculation is not repeated.
d1 = zeros(nctrlp,K);
d2 = d1;
for m=2:K
d1(:,m) = knots(index+m-1) - knots(index);
d2(:,m) = knots(index+m) - knots(index+1);
end
knots = knots(:);
knots1 = knots(1:nctrlp+1);
knots2 = knots(2:nctrlp+2);
knotSize = size(knots1);
knotc1 = knots(nctrlp+1);
knotc2 = knots(nctrlp+2);
for ui = 1:nu
% k = 1
u_ = u(ui)*ones(knotSize);
NA = u_>=knots1 & u_<knots2;
if u(ui) == umax && knotc1 == umax && knotc2 == umax
NA(1:nctrlp+1) = 0;
NA(end-1,1) = 1;
end
N(:,1) = NA;
% k > 2
for k = 2:K
p1 = (u(ui) - knots(index)) ./ d1(:,k) .* N(index,k-1);
p1(isnan(p1)) = 0;
p2 = (knots(index+k) - u(ui)) ./ d2(:,k) .* N(index+1,k-1);
p2(isnan(p2)) = 0;
N(index,k) = p1 + p2;
end
U(ui,:)=N(1:end-1,k);
end
end
function knots = getknots(ctrlp, k)
d = sqrt(sum(diff(ctrlp).^2, 2));
ds = cumsum(d)./sum(d);
knots = [zeros(k,1); ds(k-1:end); ones(k,1)];
end