<div dir="ltr">Hi Ed,<div><br></div><div>if you look at the filter weights example on the NCL website:</div><div><a href="http://www.ncl.ucar.edu/Document/Functions/Built-in/filwgts_lanczos.shtml">http://www.ncl.ucar.edu/Document/Functions/Built-in/filwgts_lanczos.shtml</a><br></div><div><br></div><div>you can see an example of how to compute the time fca value. You can do exactly the same for space.</div><div><br></div><div>time:</div><div><pre style="margin-top:0px;margin-bottom:0px;padding:0px;font-size:13px;line-height:12pt;font-family:courier;border-style:solid;border-width:0px 0px 15px;border-color:transparent;color:rgb(0,0,0)">dt = 3 days per time step
t1 = 50 days (low frequency cutoff, expressed in time domain)
t2 = 10 days (high frequency cutoff, expressed in time domain)
fca = dt/t1 = 3./50. = 0.06 time steps (low frequency cutoff)
fcb = dt/t2 = 3./10. = 0.30 time steps (high frequency cutoff)</pre><pre style="margin-top:0px;margin-bottom:0px;padding:0px;font-size:13px;line-height:12pt;font-family:courier;border-style:solid;border-width:0px 0px 15px;border-color:transparent;color:rgb(0,0,0)"><br></pre><pre style="margin-top:0px;margin-bottom:0px;padding:0px;font-size:13px;line-height:12pt;font-family:courier;border-style:solid;border-width:0px 0px 15px;border-color:transparent;color:rgb(0,0,0)"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;white-space:normal">space:</span><br></pre><pre style="margin-top:0px;margin-bottom:0px;padding:0px;line-height:12pt;border-style:solid;border-width:0px 0px 15px;border-color:transparent"><font face="arial, sans-serif"><span style="white-space:normal">dx = 100m, x1= 500m (high frequency cutoff), fca = dx/x1 = 100/500= 1/5 = 0.2 </span></font></pre><pre style="margin-top:0px;margin-bottom:0px;padding:0px;line-height:12pt;border-style:solid;border-width:0px 0px 15px;border-color:transparent"><font face="arial, sans-serif"><span style="white-space:normal"><br></span></font></pre><pre style="margin-top:0px;margin-bottom:0px;padding:0px;line-height:12pt;border-style:solid;border-width:0px 0px 15px;border-color:transparent"><font face="arial, sans-serif"><span style="white-space:normal">Hope this helps,</span></font></pre><pre style="margin-top:0px;margin-bottom:0px;padding:0px;line-height:12pt;border-style:solid;border-width:0px 0px 15px;border-color:transparent"><font face="arial, sans-serif"><span style="white-space:normal"><br></span></font></pre><pre style="margin-top:0px;margin-bottom:0px;padding:0px;line-height:12pt;border-style:solid;border-width:0px 0px 15px;border-color:transparent"><font face="arial, sans-serif"><span style="white-space:normal">Maria</span></font></pre><pre style="margin-top:0px;margin-bottom:0px;padding:0px;font-size:13px;line-height:12pt;font-family:courier;border-style:solid;border-width:0px 0px 15px;border-color:transparent;color:rgb(0,0,0)"><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;white-space:normal"><br></span></pre></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Oct 27, 2015 at 3:42 PM, yang yang <span dir="ltr"><<a href="mailto:yang.yang816@gmail.com" target="_blank">yang.yang816@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Hi Dennis:</div><div><br></div><div>Thanks for your help!</div><div><br></div><div><em>In </em>filwgts_lanczos a parameter, <em>fca</em> should be given. That is a scalar indicating the cut-off frequency of the ideal high or low-pass filter: (0.0 < <em>fca</em> < 0.5). In a 1-D spatial data, I want to filter out small scale or wavelength waves. For my case, I think that fca should be wavelength or wave numbers, instead of frequency. Suppose I have 300 data with regular 100 m spatial interval. I would to remove wavelength smaller than 500 m. How to set fca to do the filtering? Thanks!</div><div><br></div><div>Regards</div><div>Ed</div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Oct 28, 2015 at 10:20 AM, Dennis Shea <span dir="ltr"><<a href="mailto:shea@ucar.edu" target="_blank">shea@ucar.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">A filter has no idea whether the data is temporal or spatial. Most<br>
filters do assume constant spacing. If your spatial data is<br>
irregularly spaced, you will likely have to interpolate to equal<br>
spacing.<br>
<div><div><br>
On Tue, Oct 27, 2015 at 2:51 PM, yang yang <<a href="mailto:yang.yang816@gmail.com" target="_blank">yang.yang816@gmail.com</a>> wrote:<br>
> Dear Sir/Madam:<br>
><br>
> In NCL, examples of Filters using filwgts_lanczos are only in temporal<br>
> domain. Now I want to do low-pass for my 1-D spatial data such as dropsonde<br>
> data or flight-track data. Does NCL have a similar function as<br>
> filwgts_lanczos to do the work for 1-D spatial data? or How to apply<br>
> filwgts_lanczos in a 1-D spatial data? Thanks!<br>
><br>
> Regards<br>
> Ed<br>
><br>
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