NURBS

Converted NURBS toolbox

Description

The NURBS toolbox, created by Mark Spink, is a very useful tool. However, some of the routines were written in C. This is not necessarily a bad thing as long as you know how to compile them to mex files for your machine. If you don't want to mess with mex files, or you want to be able to edit the code and don't know anything about C, I've rewritten the C code in MATLAB. You can find the original toolbox at
http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=312&objectType=file

The included files replace the following mex files with the m-file equivalent.

basisfun
bspeval
bspdegelev
bspderiv
bspkntins
findspan

In addition, I've included the translated C code in the comments, line for line.

This does not include every file in the NURBS toolbox, just the mex files. You will still want to download the toolbox and replace the mex files with the included files.

• MATLAB release: MATLAB 7.3 (R2006b)
• Other requirements: NURBS Toolbox http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=312&objectType=file
• Other Files: bspderiv.m, ; bspeval.m, ; bspkntins.m, ; findspan.m, ; basisfun.m, ; bspdegelev.m

[Aslak Grinsted]

I was thinking of doing just what you have done only last friday.. Excellent to find that it already has been done. thanks

[Van Brackin]

THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU

I was having a conniption when I couldn't get Mark Spinks' programs to run compiled.

[Andre Lutz]

Very good!

But there is a mistake in nrbcoons:
If you add

hold on
nrbplot(crv1,48);
nrbplot(crv2,48);
nrbplot(crv3,48);
nrbplot(crv4,48);

before the nrbcoons command in democoons, you will see that the coons surface does not match the curves.
Fix it with replacing line 82 in nrbcoons with:

t = nrb4surf(u1.coefs(:,1), u2.coefs(:,1), u1.coefs(:,end), u2.coefs(:,end));

[Martin Lo]

This is great! Thank you so much!!! I just wasted 3 hours trying to compile the c files to mex files. The Matlab mex function is very buggy. Thanks so much!

[Richard li]

great job! Thanks

[sheethal]

I am finding several problems with this code:
1. When we increase the weights, the curve should get pulled toward the control point. But, it is moving away from the curve and vice versa

2. democurve.m hangs and MATLAB crashes. Just running it without any modification does so.

[Jesper]

I've had the same problems with the weights and fixed it in this way:
In bspeval.m between line 45 and 46, I've inserted:
for i=0:d
   N(i+1) = N(i+1)*c(4,tmp1+i);
end
N = N / sum(N);

This code applies the weights, but there is still a problem with nrbplot.m, but this is fixed by changing line 101 from
p = nrbeval(nurbs,linspace(0.0,1.0,subd));
to
[p, ggg] = nrbeval(nurbs,linspace(0.0,1.0,subd));

Where ggg is some variable, which isnt used afterwards.

Besides these small errors, this code is great. Maybe there are more error, but this works for me for now.

[haidi]

The link to the original NURBS library no longer works.
http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=312&objectType=file

Could anyone could upload it again? Thanks

[Di Xiao]

Cannot find the original NURBS Toolbox

[Eric Trautmann]

I found a copy of the NURBS toolbox (for 2006b) here:

http://webscripts.softpedia.com/script/Scientific-Engineering-Ruby/Mathematics/nurbs-33691.html

Does anyone know if there's a newer version of this?

[Ocean Yang]

Great work!

However, I find a problem in computing the first derivatives for B-spline curves/surfaces with inner multiple-knots, e.g., [0 0 0 0.5 0.5 1 1 1].

When I evaluate the first derivatives at u=0.5, it seems wrong.