Hi Mark.
I've noticed the same thing and have just learned to live with it. I assumed
it was some sort of limitation of the filter software and the ratio between
the number of points you are filtering and the size of the filter. I can
sometimes get a better result by using a none-linear filter instead of a low
pass filter.
DougO.
[EMAIL PROTECTED]
W- 613-996-6371
> ----------
> From: Marc Pelletier[SMTP:[EMAIL PROTECTED]]
> Reply To: [EMAIL PROTECTED]
> Sent: Thursday, June 29, 2000 1:07 PM
> To: [EMAIL PROTECTED]
> Subject: [geonet]: Stupid filter question
>
> Hello all,
>
> I am doing some tie line levelling. In order to create a smooth correction
> function to apply to my data I use a combination of a binary spline and a
> low pass filter on my intersection errors. My question is about the low
> pass filter. It seems that there is a very definite limit on the useful
> length of it. I've uploaded an example to
> http://www.datadonkey.com/filter.htm. In this case the line length is
> about 3000 fids and the green dots (intersection errors) are about 50 fids
> apart. The purple line is the result of the binary spline (settings of .76
> and .9) The last grey line, which you can barely see, is the filtered
> result of the purple line. In this example the low pass cutoff is set at
> 500. I expected the data to get pretty much whacked at that length. I've
> tried varying the length from 50 to 5000(!) and the results are always the
> same. The difference is in the second decimal place.
>
> Now, I'm not looking for filtering or levelling advice here. It just seems
> to me that the cutoffs don't work the way I would expect on low pass
> filtering. Can anyone comment?
>
> Thanks
>
> Marc Pelletier
>
> --------------------------------------------------------------------------
> -
> Data Donkey - Geophysical Data Processing, Consulting and Software
> Development
> Creator of the POWER TOOLBOX utilities for OASIS montaj
> contact: mailto:[EMAIL PROTECTED] tel (306) 931-6853 or
> http://www.datadonkey.com
>
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