×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Interpolation

thread575-331133

Interpolation

Interpolation

(OP)
Hello everyone,
I need to interpolate a trajectory.
The trajectory is an array with the X and Y coordinates. The problem is that, since it is not a function, there are more that one Y value for each X and vicecersa.
For example:
Trajectory:
[1 4
2 5
3 6
4 8
5 10
6 11
7 12
9 11
10 9
9 8
8 7
7 6
7 5
8 5
9 4
11 4
12 4]
I tried to use the function interp1 but it gives me an error because my trajectory is not a function.
Since the position is stored with a frequency of 14 Hz, I have lost some information of the path. This is why I need an interpolation.
Moreover I have also multiple X for the same Y. It means that transpose the X with the Y doesn't help.
How can I do it?
There is a function that interpolates trajectory and not only function?
Is there any function in Matlab that allows me to interpolate vectors?
Thanks in advance to everyone
Andrea
Replies continue below

Recommended for you

RE: Interpolation

Your biggest issue is going to be that linear interpolation will suck at accurately predicting the estimated trajectory. Your data shows lots of turns, which I assume were originally smooth changes in direction?

Are these points sufficiently accurate to use for a spline fit?

TTFN
FAQ731-376: Eng-Tips.com Forum Policies

RE: Interpolation

Interesting issue that surprisingly doesn't seem solved in the various forums. Would seem to me to be a FAQ when using interp1. Anyway, after a bit of playing I have a solution.

As you say, interp1 and friends won't do non-functions, so you need to generate an equivalent function by parameterising. By using a simple parameterisation on both the X and Y points, you get two functions that can be independently interpolated. De-parameterisation will then give you the interpolation of the original non-function.

CODE --> matlab

XY = <paste data from original post>;
X = XY(:, 1);
Y = XY(:, 2);
t = 0:0.1:17;
X1 = interp1(1:17,X,t);
Y1 = interp1(1:17,Y,t);
plot(X,Y,'o', X1,Y1,'-')

Now as IRstuff goes on to say, maybe a linear interpolation is not ideal. Good news is that other interpolation functions slot right in:

CODE --> matlab

X1 = pchip(1:17,X,t);
Y1 = pchip(1:17,Y,t);
plot(X,Y,'o', X1,Y1,'-')

CODE --> matlab

X1 = spline(1:17,X,t);
Y1 = spline(1:17,Y,t);
plot(X,Y,'o', X1,Y1,'-')

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


News
Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close