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

planePosition(point, plane)
```function pos = planePosition(point, plane)
%PLANEPOSITION Compute position of a point on a plane
%
%   PT2 = planePosition(POINT, PLANE)
%   POINT has format [X Y Z], and plane has format
%   [X0 Y0 Z0  DX1 DY1 DZ1  DX2 DY2 DZ2], where :
%   - (X0, Y0, Z0) is a point belonging to the plane
%   - (DX1, DY1, DZ1) is a first direction vector
%   - (DX2, DY2, DZ2) is a second direction vector
%
%   Result PT2 has the form [XP YP], with [XP YP] coordinate of the point
%   in the coordinate system of the plane.
%
%
%   CAUTION:
%   WORKS ONLY FOR PLANES WITH ORTHOGONAL DIRECTION VECTORS
%
%   Example
%     plane = [10 20 30  1 0 0  0 1 0];
%     point = [13 24 35];
%     pos = planePosition(point, plane)
%     pos =
%         3   4
%
%   See also:
%   geom3d, planes3d, points3d, planePoint

%   ---------
%   author : David Legland
%   INRA - TPV URPOI - BIA IMASTE
%   created the 21/02/2005.
%

%   HISTORY
%   24/11/2005 add support for multiple inputs

% size of input arguments
npl = size(plane, 1);
npt = size(point, 1);

% check inputs have compatible sizes
if npl ~= npt && npl > 1 && npt > 1
error('geom3d:planePoint:inputSize', ...
'plane and point should have same size, or one of them must have 1 row');
end

% origin and direction vectors of the plane
p0 = plane(:, 1:3);
d1 = plane(:, 4:6);
d2 = plane(:, 7:9);

% Compute dot products with direction vectors of the plane
if npl > 1 || npt == 1
s = dot(bsxfun(@minus, point, p0), d1, 2) ./ vectorNorm3d(d1);
t = dot(bsxfun(@minus, point, p0), d2, 2) ./ vectorNorm3d(d2);
else
% we have npl == 1 and npt > 1
d1 = d1 / vectorNorm3d(d1);
d2 = d2 / vectorNorm3d(d2);
inds = ones(npt,1);
s = dot(bsxfun(@minus, point, p0), d1(inds, :), 2);
t = dot(bsxfun(@minus, point, p0), d2(inds, :), 2);
end

% % old version:
% s = dot(point-p0, d1, 2) ./ vectorNorm3d(d1);
% t = dot(point-p0, d2, 2) ./ vectorNorm3d(d2);

pos = [s t];

```

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