Detect abrupt change in trajectory (coordinates)

I have a trajectory (cartesian) on a timeline (frames) and I need to find abrupt changes in trajectory, i.e. almost 180º. I found this: https://uk.mathworks.com/matlabcentral/answers/177523-detecting-path-trajectory-turns-in-tracking-data

but that script example doesn't seem to work very well for me (select frames in a straight line...) and I don't understand it well enough to fix it.

I have attached a example dataset with 3 columns: x, y (coordinates), frame nb (time). On this example, the first abrupt chang of trajectory should be found at around frame # 37.

I would be very grateful for any help!

Many thanks

[darova]

I plotted your data

But i don't see any abrupt data like 180 degree

[Butterflyfish]

Did you plot (x,y)? This is how the trajectory should look:

d = load('sampletrajectory.mat');
plot(d.trajectories1.pos_x, d.trajectories1.pos_y)

Answer 1

[darova]

What about this? Just diff and atan2d

load sampletrajectory.mat
tr = table2array(trajectories1);        % convert to array
x = tr(:,2);                            % x coord
y = tr(:,3);                            % y coord
t = atan2d(diff(y),diff(x));            % angle of each line
dt = wrapTo180(diff(t));                % angle between lines
ix = find(abs(dt)>150);                 % find angle
cla
plot(x(ix+1),y(ix+1),'or')              % plot the angle
line(x,y)                               % plot the data
hold on
for i = 1:length(ix)
    text(x(ix(i)+1),y(ix(i)+1),num2str(dt(ix(i))))
end
hold off

[Butterflyfish]

This is working like a treat! Thank you so much!

Would you be able to explain to me in more details what atan2d and wrapTo180 do in this context? It is just so that I can understand fully what that script is doing! Thanks again for your help.

[darova]

• what atan2d and wrapTo180 do in this context?

Those functions do exactly as i wrote in comments:

t = atan2d(diff(y),diff(x));            % angle of each line
dt = wrapTo180(diff(t));                % angle between lines

aran2d calculates angle ( )

diff calculates difference between angles

wrapTo180 wraps angle to 0.. 180 degree range (if angle is 350 degree the function returns 10)

[Butterflyfish]

Great, many thanks!