Spline interpolation and alternative interpolation

[DonRoth]

Hi Folks:

I don't know if the last post made it so I am resubmitting.

The attached code with test.vi as the main VI shows spline interpolation of an irregularly-spaced 1d array. In sparsely-populated data areas, unwanted peaks and/or valleys result that do not follow the form of the original data. Short of doing curve fitting (which has its own problems), is there a modification or variation of spline interpolation that might truly follow the form of the original data?

Thanks,

Don

[DonRoth]

The message board does not seem to want to let me post the LLB so I would like to email it to those interested in this post....Don

[DonRoth]

Looks like the attachment made it this last time.....Don

[Matt_F]

Hello DonRoth,

The behavior we are seeing with the Spline Interpolation is intrinsic of the operation and therefore expected when we have sparsely populated areas of data.

While LabVIEW currently does not have other types of spline interpolations, it can call external code to perform the operation. A search of Google will probably yield publicly available implementations of cubic or B-Splines that may be more appropriate in this application.

Please let me know if you have any more questions about this.

Regards,

Matt F

[Bob_Y.]

I don't know the answer to the problem asked, but I have found a different problem using the VIs that show the spline problem (see the second post in the link below). The input graph on test.vi is totally messed up. The data is obviously stored correctly as the VI runs, but the front panel control is not at all right. There is no grid and there is no data. In fact, there is no data display area. If I grab the right or left edges, it immediately extends them off the screen. It is weird.

I just updated to LabVIEW 7.1.1 and I was wondering if that was the problem, but a co-worker opened it in 7.1 and he saw the same thing.

Anyone know what happened to this graph? Is this a bug of some sort?

Thanks,
Bob Young

[DonRoth]

Here is what it looks like when I open it (looks fine)...Don

[DonRoth]

Again seem to be having trouble posting attachments. Trying again right now....Don

[Ben]

I beleive thre was an issue with attaching a doc and then doing a spell check.

Check that your attachment is correct just before you hit "submt Post".

Ben

[Matt_F]

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@BOB Y. wrote:
I don't know the answer to the problem asked, but I have found a different problem using the VIs that show the spline problem (see the second post in the link below). The input graph on test.vi is totally messed up. The data is obviously stored correctly as the VI runs, but the front panel control is not at all right. There is no grid and there is no data. In fact, there is no data display area. If I grab the right or left edges, it immediately extends them off the screen. It is weird.

---

I saw the same behavior on my system and was able to format it properly by right clicking on the graph and selecting Advanced >> Reset Scale Layout. Attached below is the VI with the proper formatting.

I do not know why this is occurring and it appears to be an isolated case. Please let me know if you are able to reproduce this behavior.

Regards,

Matt F

[Gurdas]

Hi Matt,

We are observing similar problem and I wanted to know if things have improved since your post.

What we observe is that if the points are spaced equidistant, the spline comes OK. In other cases there is distortion.

Thanks,

Gurdas