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geom2d

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geom2d

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13 Jun 2005 (Updated )

Geometry library for matlab. Performs geometric computations on points, lines, circles, polygons...

parametrize(varargin)
function par = parametrize(varargin)
%PARAMETRIZE Parametrization of a polyline, based on edges lengths
%
%   PAR = parametrize(POLY);
%   Returns a parametrization of the curve defined by the serie of points,
%   based on euclidean distance between two consecutive points. 
%   POLY is a N-by-2 array, representing coordinates of vertices. The
%   result PAR is N-by-1, and contains the cumulative length of edges until
%   corresponding vertex.
%
%   PAR = parametrize(PX, PY);
%   is the same, but specify points coordinates in separate column vectors.
%
%   PAR = parametrize(..., 'normalize', 1);
%   PAR = parametrize(..., 'normalize', true);
%   Rescales the result such that the last element of PAR is 1.
% 
%   Example
%     % Parametrize a circle approximation
%     poly = circleToPolygon([0 0 1], 200);
%     p = parametrize(poly);
%     p(end)
%     ans = 
%         6.2829
%
%   See also:
%   polygons2d, polylineLength
%
%   ---------
%   author : David Legland 
%   INRA - TPV URPOI - BIA IMASTE
%   created the 06/04/2003.
%


%% Process inputs

% extract vertex coordinates
if size(varargin{1}, 2) > 1
    % vertices in a single array
    pts = varargin{1};
    varargin(1) = [];
    
elseif length(varargin) == 2
    % points as separate arrays
    pts = [varargin{1} varargin{2}];
    varargin(1:2) = [];
    
end

% by default, do not normalize
normalize = false;

% extract options
while length(varargin) > 1
    param = varargin{1};
    switch lower(param)
        case 'normalize'
            normalize = varargin{2};
        otherwise
            error('Unknown parameter name: %s', param);
    end
    varargin(1:2) = [];
end


%% Parametrize polyline

% compute cumulative sum of euclidean distances between consecutive
% vertices, setting distance of first vertex to 0.
if size(pts, 2) == 2
    % process points in 2D
    par = [0 ; cumsum(hypot(diff(pts(:,1)), diff(pts(:,2))))];
else
    % process points in arbitrary dimension
    par = [0 ; cumsum(sqrt(sum(diff(pts).^2, 2)))];
end

% eventually rescale between 0 and 1
if normalize
    par = par / par(end);
end

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