13 Jun 2005
01 Apr 2014)
Geometry library for matlab. Performs geometric computations on points, lines, circles, polygons...
function point = projPointOnLine(point, line)
%PROJPOINTONLINE Project of a point orthogonally onto a line
% PT2 = projPointOnLine(PT, LINE).
% Computes the (orthogonal) projection of point PT onto the line LINE.
% Function works also for multiple points and lines. In this case, it
% returns multiple points.
% Point PT1 is a [N*2] array, and LINE is a [N*4] array (see createLine
% for details). Result PT2 is a [N*2] array, containing coordinates of
% orthogonal projections of PT1 onto lines LINE.
% line = [0 2 2 1];
% projPointOnLine([3 1], line)
% ans =
% 2 3
% See also:
% lines2d, points2d, isPointOnLine, linePosition
% author : David Legland
% INRA - TPV URPOI - BIA IMASTE
% created the 07/04/2005.
% 2005-08-06 correct bug when several points were passed as param.
% 2012-08-23 remove repmats
% direction vector of the line
vx = line(:, 3);
vy = line(:, 4);
% difference of point with line origin
dx = point(:,1) - line(:,1);
dy = point(:,2) - line(:,2);
% Position of projection on line, using dot product
tp = (dx .* vx + dy .* vy ) ./ (vx .* vx + vy .* vy);
% convert position on line to cartesian coordinates
point = [line(:,1) + tp .* vx, line(:,2) + tp .* vy];