Code covered by the BSD License

# geom3d

### David Legland (view profile)

19 Jun 2009 (Updated )

Library to handle 3D geometric primitives: create, intersect, display, and make basic computations

### Editor's Notes:

This file was selected as MATLAB Central Pick of the Week

angleSort3d(pts, varargin)
```function varargout = angleSort3d(pts, varargin)
%ANGLESORT3D Sort 3D coplanar points according to their angles in plane
%
%   PTS2 = angleSort3d(PTS);
%   Considers all points are located on the same plane, and sort them
%   according to the angle on plane. PTS is a [Nx2] array. Note that the
%   result depend on plane orientation: points can be in reverse order
%   compared to expected. The reference plane is computed besed on the 3
%   first points.
%
%   PTS2 = angleSort3d(PTS, PTS0);
%   Computes angles between each point of PTS and PT0. By default, uses
%   centroid of points.
%
%   PTS2 = angleSort3d(PTS, PTS0, PTS1);
%   Specifies the point which will be used as a start.
%
%   [PTS2, I] = angleSort3d(...);
%   Also return in I the indices of PTS, such that PTS2 = PTS(I, :);
%
%   points3d, angles3d, angleSort
%
% ------
% Author: David Legland
% e-mail: david.legland@grignon.inra.fr
% Created: 2005-11-24
% Copyright 2005 INRA - CEPIA Nantes - MIAJ (Jouy-en-Josas).

%   HISTORY :
%   04/01/2007: remove unused variables

% default values
pt0     = mean(pts, 1);
pt1     = pts(1,:);

if length(varargin)==1
pt0 = varargin{1};
elseif length(varargin)==2
pt0 = varargin{1};
pt1 = varargin{2};
end

% create support plane
plane   = createPlane(pts(1:3, :));

% project points onto the plane
pts2d   = planePosition(pts, plane);
pt0     = planePosition(pt0, plane);
pt1     = planePosition(pt1, plane);

% compute origin angle
theta0  = atan2(pt1(2)-pt0(2), pt1(1)-pt0(1));
theta0  = mod(theta0 + 2*pi, 2*pi);

% translate to reference point
n       = size(pts, 1);
pts2d   = pts2d - repmat(pt0, [n 1]);

% compute angles
angle   = atan2(pts2d(:,2), pts2d(:,1));
angle   = mod(angle - theta0 + 4*pi, 2*pi);

% sort points according to angles
[angle, I] = sort(angle); %#ok<ASGLU>

% format output
if nargout<2
varargout{1} = pts(I, :);
elseif nargout==2
varargout{1} = pts(I, :);
varargout{2} = I;
end

```