How can I find the intersection points of two vectors that do not (necessarily) contain the value at the intersection point?

Hi,

I have a vector of angular velocity data sampled at 128Hz (and a corresponding time vector) and I am trying to find out how many times the velocity crosses a specific velocity threshold (e.g., +/-30 deg/s). Importantly, the vector of velocity data may not contain the exact value of the threshold (i.e., it may contain 29.5 and 31 degs/s but not 30 deg/s).

Additionally, I want to impose a minimum distance of 100ms (about 13 samples) between consecutive intersection points. The final objective is to then plot the intersection points onto the velocity as a function of time and obtain the number of times it crossed the threshold.

Thanks in advance for any answers!

[darova]

Do you have data?

[Gian-Luca Gubler]

Absolutely. I have attached a data file with a velocity and time vector.

Answer 1

[KSSV]

Try this:

https://in.mathworks.com/matlabcentral/fileexchange/22441-curve-intersections?focused=5165138&tab=function

[Gian-Luca Gubler]

Thank you, this works great!

[Gian-Luca Gubler]

Since you answered the main question outlined in my title, I accepted your answer. However, I am still unsure how to impose a minimum distance between consecutive intersection points. I now have the (x,y) coordinates of all intersection points and want to ensure that all consecutive intersection points are separated by at least 0.1 along the x-axis, i.e., delete points from the array that do not meet this criterion.

The problem I am facing is that removing points from the array changes the distances between consecutive points. For example, three intersection points might be too close together (0ms, 50ms, 100ms) but removing the middle point results in a distance between the two remaining points that is sufficient.

Should I post a new question for this?

[KSSV]

You have (x,y) points......so create your desired x with required spacing and use interpolation.

[Gian-Luca Gubler]

How exactly would I go about doing this?

Let's say I have

P = [30,7.78;30,9.30;-30,10.20;-30,11.60;30,12.00;30,12.033;30,12.066;30,12.1]

Rows (intersection points) 6 and 7 should be removed from the array because they are too close in time (2nd column). However, rows 5 and 8 should remain in the array because the distance between those two is 0.1 once rows 6 and 7 are removed.

[KSSV]

Interpolation will not work.....you need to get the distance set a condition and remove the elements.

[Gian-Luca Gubler]

Exactly. Could you show me how you would do that?