drawellipse

 function h = drawellipse(x,y,ang,sd1,sd2,theta0,theta1,linestyle,granularity)

 <x> is x-position of ellipse center
 <y> is y-position of ellipse center
 <ang> is the orientation in [0,2*pi).  0 means major axis is parallel to x-axis.
 <sd1> is the std dev along the major axis
 <sd2> is the std dev along the minor axis
 <theta0> (optional) is the starting angle in [0,2*pi).  default: 0.
 <theta1> (optional) is the ending angle in [0,2*pi].  default: 2*pi.
 <linestyle> (optional) is like 'r-'.  default: 'r-'.
   special case is {C} where C is a color char, scalar, or vector.
   in this case, a patch object is created instead of a line object.
 <granularity> (optional) is how many points in a complete revolution.  default: 360.

 draw a complete or partial ellipse on the current figure.  the ellipse corresponds 
 to +/- 1 standard deviation along the major and minor axes.  we proceed CCW from 
 <theta0> to <theta1>.  return the handle to the line object that we create.

 example:
 figure; drawellipse(3,1,pi/6,3,1,0,3*pi/2,'ro-',50); axis equal;

0001 function h = drawellipse(x,y,ang,sd1,sd2,theta0,theta1,linestyle,granularity)
0002 
0003 % function h = drawellipse(x,y,ang,sd1,sd2,theta0,theta1,linestyle,granularity)
0004 %
0005 % <x> is x-position of ellipse center
0006 % <y> is y-position of ellipse center
0007 % <ang> is the orientation in [0,2*pi).  0 means major axis is parallel to x-axis.
0008 % <sd1> is the std dev along the major axis
0009 % <sd2> is the std dev along the minor axis
0010 % <theta0> (optional) is the starting angle in [0,2*pi).  default: 0.
0011 % <theta1> (optional) is the ending angle in [0,2*pi].  default: 2*pi.
0012 % <linestyle> (optional) is like 'r-'.  default: 'r-'.
0013 %   special case is {C} where C is a color char, scalar, or vector.
0014 %   in this case, a patch object is created instead of a line object.
0015 % <granularity> (optional) is how many points in a complete revolution.  default: 360.
0016 %
0017 % draw a complete or partial ellipse on the current figure.  the ellipse corresponds
0018 % to +/- 1 standard deviation along the major and minor axes.  we proceed CCW from
0019 % <theta0> to <theta1>.  return the handle to the line object that we create.
0020 %
0021 % example:
0022 % figure; drawellipse(3,1,pi/6,3,1,0,3*pi/2,'ro-',50); axis equal;
0023 
0024 % input
0025 if ~exist('theta0','var') || isempty(theta0)
0026   theta0 = 0;
0027 end
0028 if ~exist('theta1','var') || isempty(theta1)
0029   theta1 = 2*pi;
0030 end
0031 if ~exist('linestyle','var') || isempty(linestyle)
0032   linestyle = 'r-';
0033 end
0034 if ~exist('granularity','var') || isempty(granularity)
0035   granularity = 360;
0036 end
0037 
0038 % deal with thetas for wrap-around case
0039 if theta1 < theta0
0040   theta1 = theta1 + 2*pi;
0041 end
0042 
0043 % prep figure
0044 hold on;
0045 
0046 % figure out thetas that we want
0047 thetas = linspace(theta0,theta1,ceil((theta1-theta0)/(2*pi) * (granularity+1)));
0048 
0049 % figure out the base coordinates
0050 [X,Y] = pol2cart(thetas,1);
0051 coord = [X; Y];
0052 
0053 % scale
0054 coord = diag([sd1 sd2]) * coord;
0055 
0056 % rotate   [cos(ang) sin(ang); -sin(ang) cos(ang)] rotates CW
0057 coord = [cos(-ang) sin(-ang); -sin(-ang) cos(-ang)]*coord;
0058 
0059 % translate     [TODO: TRANSFORMATIONS SHOULD BE CLEANED UP AND MADE INTO FUNCTIONS!]
0060 coord(1,:) = coord(1,:) + x;
0061 coord(2,:) = coord(2,:) + y;
0062 
0063 % do it
0064 if iscell(linestyle)
0065   h = patch(coord(1,:),coord(2,:),linestyle{1});
0066 else
0067   h = plot(coord(1,:),coord(2,:),linestyle);
0068 end