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

intersectLinePlane(line, plane, varargin)
function point = intersectLinePlane(line, plane, varargin)
%INTERSECTLINEPLANE Intersection point between a 3D line and a plane
%
%   PT = intersectLinePlane(LINE, PLANE)
%   Returns the intersection point of the given line and the given plane.
%   LINE:  [x0 y0 z0 dx dy dz]
%   PLANE: [x0 y0 z0 dx1 dy1 dz1 dx2 dy2 dz2]
%   PT:    [xi yi zi]
%   If LINE and PLANE are parallel, return [NaN NaN NaN].
%   If LINE (or PLANE) is a matrix with 6 (or 9) columns and N rows, result
%   is an array of points with N rows and 3 columns.
%
%   PT = intersectLinePlane(LINE, PLANE, TOL)
%   Specifies the tolerance factor to test if a line is parallel to a
%   plane. Default is 1e-14.
%
%   Example
%     % define horizontal plane through origin
%     plane = [0 0 0   1 0 0   0 1 0];
%     % intersection with a vertical line
%     line = [2 3 4  0 0 1];
%     intersectLinePlane(line, plane)
%     ans =
%        2   3   0
%     % intersection with a line "parallel" to plane
%     line = [2 3 4  1 2 0];
%     intersectLinePlane(line, plane)
%     ans =
%       NaN  NaN  NaN
%
%   lines3d, planes3d, points3d, clipLine3d
%
%   ---------
%   author : David Legland
%   INRA - TPV URPOI - BIA IMASTE
%   created the 17/02/2005.
%

%   HISTORY
%   24/11/2005 add support for multiple input
%   23/06/2006 correction from Songbai Ji allowing different number of
%       lines or plane if other input has one row
%   14/12/2006 correction for parallel lines and plane normals
%   05/01/2007 fixup for parallel lines and plane normals
%   24/04/2007 rename as 'intersectLinePlane'
%   11/19/2010 Added bsxfun functionality for improved speed (Sven Holcombe)
%   01/02/2011 code cleanup, add option for tolerance, update doc

% extract tolerance if needed
tol = 1e-14;
if nargin > 2
tol = varargin{1};
end

% unify sizes of data
nLines  = size(line, 1);
nPlanes = size(plane, 1);

% N planes and M lines not allowed
if nLines ~= nPlanes && min(nLines, nPlanes) > 1
error('MatGeom:geom3d:intersectLinePlane', ...
'Input must have same number of rows, or one must be 1');
end

% plane normal
n = vectorCross3d(plane(:,4:6), plane(:,7:9));

% difference between origins of plane and line
dp = bsxfun(@minus, plane(:, 1:3), line(:, 1:3));

% dot product of line direction with plane normal
denom = sum(bsxfun(@times, n, line(:,4:6)), 2);

% relative position of intersection point on line (can be inf in case of a
% line parallel to the plane)
t = sum(bsxfun(@times, n, dp),2) ./ denom;

% compute coord of intersection point
point = bsxfun(@plus, line(:,1:3),  bsxfun(@times, [t t t], line(:,4:6)));

% set indices of line and plane which are parallel to NaN
par = abs(denom) < tol;
point(par,:) = NaN;