function [checkPt, onEnd] = checkPointOnSegment(segment, C, delta1, delta2)

% Check if a point C lies on a line segment
% Vipul Lugade
% Matlabgeeks.com
% 9/9/2018

% e.g. segment = [P1_X, P1_Y; P2_X, P2_Y]; C = [CX, CY];

%% initialize outputs
checkPt = false;
onEnd = false;

%% Error check
if any(size(segment) ~=2) || numel(C) ~= 2
    error('Point/segment arguments not properly defined.');
end

%% Perform cross product to see if the vectors formed by both endpoints
% and the point in question are collinear
A = segment(1,:);
B = segment(2,:);

% form vectors for the line segment (AB) and the point to one endpoint of
% segment
AB = B - A;
AC = C - A;

% if not collinear then return false as point cannot be on segment
if abs(cross(AB, AC)) < delta1
    % calculate the dotproduct of (AB, AC) and (AB, AB) to see point is now
    % on the segment
    dotAB = dot(AB, AB);
    dotAC = dot(AB, AC);
    % on end points of segment
    if abs(dotAC) < delta2 || abs(dotAC - dotAB) < delta2
        onEnd = true;
        checkPt = true;
    % on segment
    elseif dotAC > delta2 && dotAC < dotAB
        checkPt = true;
    end
end

%% plot the results
% if plotResults
%     figure; hold on;
%     plot(segment(:,1), segment(:,2), 'ro-');
%     plot(C(1), C(2), 'bs');
%     legend('segment', 'point');
%     if checkPt
%         text(C(1)+0.1, C(2)+0.1, 'Point on Segment');
%     else
%         text(C(1)+0.1, C(2)+0.1, 'Point Not on Segment');
%     end
% end

%% Cross product returning z value
function z = cross(a, b)
    z = a(1)*b(2) - a(2)*b(1);