nrbdegelev.m

强大的nurbs的工具箱 nurbs曲线

function inurbs = nrbdegelev(nurbs, ntimes)
% 
% Function Name:
% 
%   nrbdegelev - Elevate the degree of the NURBS curve or surface.
% 
% Calling Sequence:
% 
%   ecrv = nrbdegelev(crv,utimes);
%   esrf = nrbdegelev(srf,{utimes,vtimes});
% 
% Parameters:
% 
%   crv		: NURBS curve, see nrbmak.
% 
%   srf		: NURBS surface, see nrbmak.
% 
%   utimes	: Increase the degree along U direction utimes.
% 
%   vtimes	: Increase the degree along V direction vtimes.
% 
%   ecrv	: new NURBS structure for a curve with degree elevated.
% 
%   esrf        : new NURBS structure for a surface with degree elevated.
% 
% 
% Description:
% 
%   Degree elevates the NURBS curve or surface. This function uses the
%   B-Spline function bspdegelev, which interface to an internal 'C'
%   routine.
% 
% Examples:
% 
%   Increase the NURBS surface twice along the V direction.
%   esrf = nrbdegelev(srf, 0, 1); 
% 
% See:
% 
%   bspdegelev

%  D.M. Spink
%  Copyright (c) 2000.

if nargin < 2
  error('Input argument must include the NURBS and degree increment.');
end

if ~isstruct(nurbs)
  error('NURBS representation is not structure!');
end

if ~strcmp(nurbs.form,'B-NURBS')
  error('Not a recognised NURBS representation');
end

degree = nurbs.order-1;

if iscell(nurbs.knots)
  % NURBS represents a surface
  [dim,num1,num2] = size(nurbs.coefs);

  % Degree elevate along the v direction
  if ntimes(2) == 0
    coefs = nurbs.coefs;
    knots{2} = nurbs.knots{2};
  else
    coefs = reshape(nurbs.coefs,4*num1,num2);
    [coefs,knots{2}] = bspdegelev(degree(2),coefs,nurbs.knots{2},ntimes(2));
    num2 = size(coefs,2);
    coefs = reshape(coefs,[4 num1 num2]);
  end

  % Degree elevate along the u direction
  if ntimes(1) == 0
    knots{1} = nurbs.knots{1};
  else
    coefs = permute(coefs,[1 3 2]);
    coefs = reshape(coefs,4*num2,num1);
    [coefs,knots{1}] = bspdegelev(degree(1),coefs,nurbs.knots{1},ntimes(1));
    coefs = reshape(coefs,[4 num2 size(coefs,2)]);
    coefs = permute(coefs,[1 3 2]);
  end 
  
else

  % NURBS represents a curve
  if isempty(ntimes)
    coefs = nurbs.coefs;
    knots = nurbs.knots;
  else
    [coefs,knots] = bspdegelev(degree,nurbs.coefs,nurbs.knots,ntimes);
  end
  
end

% construct new NURBS
inurbs = nrbmak(coefs,knots);