| Re: Interpolating Irregular 2D Data [message #8606] |
Wed, 26 March 1997 00:00 |
peter
Messages: 80
Registered: February 1994
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Member |
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Achim Hein (hein@nv.et-inf.uni-siegen.de) wrote:
: Bijan Pesaran wrote:
: >
: > I have z=(x,y) data on a spiral and I want to sample it on a
: > grid for further manipulations, specifically kernel smoothing.
: >
: But I think the faster way is to interpolate the irregular data down to
: equidistant twodimensional axis - simultaneously, you smooth your data
: because of the interpolating.
Achim's suggestion is a good way to go -- the data on the spiral can be
placed onto a grid and smoothed at the same time by the procedure known
as gridding (essentially, convolving the non-rectilinear data with a
smoothing kernel onto the grid points). Very hard to do fast in IDL,
due to required (?) nested loops, since potentially every data point
lies at unique distances from its surrounding grid points, and thus
requires calculation of the interpolation weights; I've used a
call_external program to do it rapidly (and, in fact, to do spiral to
rectilinear conversion).
Peter
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| Re: Interpolating Irregular 2D Data [message #8648 is a reply to message #8606] |
Fri, 21 March 1997 00:00  |
Achim Hein
Messages: 42
Registered: February 1996
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Member |
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Bijan Pesaran wrote:
>
> Hi,
>
> I have z=(x,y) data on a spiral and I want to sample it on a
> grid for further manipulations, specifically kernel smoothing.
>
> I don't see how to use interpolate or bilinear to do this. They both
> seem to require the input data to be on a grid already ...
>
I think there are two possibilities of soluting this problem:
First, you can oversample your signal by zero padding in the frequency
domain to get higher resolution in the time domain. If you take the
oversampling factor big enough, you can sample your data down to the
grid.
But I think the faster way is to interpolate the irregular data down to
equidistant twodimensional axis - simultaneously, you smooth your data
because of the interpolating.
Cheers
Achim
--
_______________________________________________
Dipl.-Ing. A. Hein
PB2 / ZESS - Uni-GH-Siegen
Paul-Bonatz Str. 9-11
57068 Siegen
Phone: 0271/740-3362
Fax: 0271/740-2336
Mail: Hein@nv.et-inf.uni-siegen.de
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Please have a look at our Web-Sites:
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