Draw a cube

Simple function to draw a voxel (cube, cuboid) in a specific position of specific dimensions in a 3-D plot. Transparency of the voxel can also be specified.

Many voxels can be aggregated to form a different shapes (a simple 3-D "+" is shown in the screenshot).

Written by Joel Suresh

function voxel(i,d,c,alpha);

%VOXEL function to draw a 3-D voxel in a 3-D plot
%
%Usage
%   voxel(start,size,color,alpha);
%
%   will draw a voxel at 'start' of size 'size' of color 'color' and
%   transparency alpha (1 for opaque, 0 for transparent)
%   Default size is 1
%   Default color is blue
%   Default alpha value is 1
%
%   start is a three element vector [x,y,z]
%   size the a three element vector [dx,dy,dz]
%   color is a character string to specify color
%       (type 'help plot' to see list of valid colors)
%
%
%   voxel([2 3 4],[1 2 3],'r',0.7);
%   axis([0 10 0 10 0 10]);
%

%   Suresh Joel Apr 15,2003
%           Updated Feb 25, 2004

switch(nargin),
case 0
    disp('Too few arguements for voxel');
    return;
case 1
    l=1;    %default length of side of voxel is 1
    c='b';  %default color of voxel is blue
case 2,
    c='b';
case 3,
    alpha=1;
case 4,
    %do nothing
otherwise
    disp('Too many arguements for voxel');
end;

x=[i(1)+[0 0 0 0 d(1) d(1) d(1) d(1)]; ...
        i(2)+[0 0 d(2) d(2) 0 0 d(2) d(2)]; ...
        i(3)+[0 d(3) 0 d(3) 0 d(3) 0 d(3)]]';

for n=1:3
    if n==3,
        x=sortrows(x,[n,1]);
    else
        x=sortrows(x,[n n+1]);
    end;
    temp=x(3,:);
    x(3,:)=x(4,:);
    x(4,:)=temp;
    h=patch(x(1:4,1),x(1:4,2),x(1:4,3),c);
    set(h,'FaceAlpha',alpha);
    temp=x(7,:);
    x(7,:)=x(8,:);
    x(8,:)=temp;
    h=patch(x(5:8,1),x(5:8,2),x(5:8,3),c);
    set(h,'FaceAlpha',alpha);
end

Draw a circle

I track visitors to my site using google analytics and I noticed I had 8 visitors to my site last week looking for how to draw a circle. However I didn't have any circle drawing snippets. So I have borrowed some code from the Mathworks file exchange.

This code is courtesy of Zhenhai Wang.

function H=circle(center,radius,NOP,style)
%-----------------------------------------------------
% H=CIRCLE(CENTER,RADIUS,NOP,STYLE)
% This routine draws a circle with center defined as
% a vector CENTER, radius as a scaler RADIS. NOP is
% the number of points on the circle. As to STYLE,
% use it the same way as you use the rountine PLOT.
% Since the handle of the object is returned, you
% use routine SET to get the best result.
%
%   Usage Examples,
%
%   circle([1,3],3,1000,':');
%   circle([2,4],2,1000,'--');
%
%   Zhenhai Wang <zhenhai@ieee.org>
%   Version 1.00
%   December, 2002
%-----------------------------------------------------

if (nargin <3),
 error('Please see help for INPUT DATA.');
elseif (nargin==3)
    style='b-';
end;
THETA=linspace(0,2*pi,NOP);
RHO=ones(1,NOP)*radius;
[X,Y] = pol2cart(THETA,RHO);
X=X+center(1);
Y=Y+center(2);
H=plot(X,Y,style);
axis square;