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

fillSphericalTriangle(sphere, p1, p2, p3, varargin)
```function varargout = fillSphericalTriangle(sphere, p1, p2, p3, varargin)
%FILLSPHERICALTRIANGLE Fill a triangle on a sphere
%
%   fillSphericalTriangle(SPHERE, PT1, PT2, PT3);
%
%
%   See also
%   fillSphericalPolygon, drawSphericalTriangle, drawSphere
%
%   ---------
%   author : David Legland
%   INRA - TPV URPOI - BIA IMASTE
%   created the 22/02/2005
%

%   HISTORY
%   27/06/2007 manage spheres other than origin
%   30/10/2008 replace intersectPlaneLine by intersectLinePlane
%   2012-02-09 rename as fillSphericalTriangle

% extract data of the sphere
ori = sphere(:, 1:3);
r   = sphere(4);

% extract direction vectors for each point
v1  = normalizeVector3d(p1 - ori);
v2  = normalizeVector3d(p2 - ori);
v3  = normalizeVector3d(p3 - ori);

% create a plane tangent to the sphere containing first point
plane = createPlane(v1, v1);

% position on the plane of the direction vectors
pp2 = planePosition(intersectLinePlane([ori v2], plane), plane);
pp3 = planePosition(intersectLinePlane([ori v3], plane), plane);

% create rough parametrization with 2 variables
nTri = 5;
s  = linspace(0, 1, nTri);
t  = linspace(0, 1, nTri);
ns = length(s);
nt = length(t);
s  = repmat(s, [nt, 1]);
t  = repmat(t', [1, ns]);

% convert to plane coordinates
xp = s * pp2(1) + t .* (1-s) * pp3(1);
yp = s * pp2(2) + t .* (1-s) * pp3(2);

% convert to 3D coordinates (still on the 3D plane)
x  = plane(1) * ones(size(xp)) + plane(4) * xp + plane(7) * yp - ori(1);
y  = plane(2) * ones(size(xp)) + plane(5) * xp + plane(8) * yp - ori(2);
z  = plane(3) * ones(size(xp)) + plane(6) * xp + plane(9) * yp - ori(3);

% project on the sphere
norm = hypot(hypot(x, y), z);
xn = x ./ norm * r + ori(1);
yn = y ./ norm * r + ori(2);
zn = z ./ norm * r + ori(3);

if nargout == 0
% simply display the patch
surf(xn, yn, zn, 'FaceColor', 'g', 'EdgeColor', 'none', varargin{:});

elseif nargout == 1
% display the patch and return a handle
h = surf(xn, yn, zn, 'FaceColor', 'g', 'EdgeColor', 'none', varargin{:});
varargout = {h};

elseif nargout == 3
% If 3 outputs are required, return patch vertex coordinates
varargout = {x, y, z};
end
```

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