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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I would offer a slightly different take on inverse distance weighting. All inverse distance weighting is proportional to inverse distance to a power, so there
is never a case where an individual farther away point has more influence than an individual near point. It’s just that as the power approaches 0 then then the weights approach 1, so all points in the search radius approach being equally weighted, and if there
are more far points than near, then they will have the stronger influence as a group.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">In the case of large powers, as the power approaches infinity, the weight of the nearest point becomes much, much greater than any others and inverse distance
weighting interpolations becomes equivalent to a nearest neighbor approach. This is essentially what the previous response was saying as well.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Cheers,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">--Kenton Ross<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext"> Qgis-user <qgis-user-bounces@lists.osgeo.org>
<b>On Behalf Of </b>J.O.Williams<br>
<b>Sent:</b> Tuesday, September 17, 2019 1:24 PM<br>
<b>To:</b> qgis-user@lists.osgeo.org<br>
<b>Subject:</b> [EXTERNAL] Re: [Qgis-user] Question about Weighting Power value when running Grid-Inverse Distance to a Power<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p>A power of 1 is a linear interpolation among all points in the search radius.<o:p></o:p></p>
<p><o:p> </o:p></p>
<p>A power of 2 causes the "closest point" in the search radius to have a slightly higher weight.<o:p></o:p></p>
<p><o:p> </o:p></p>
<p>A power of 4, 6 and especially 10 causes the closest point to behave like a polygonal or theissen polygon.<o:p></o:p></p>
<p><o:p> </o:p></p>
<p>A power of 0.5 causes the farther away points to have a larger influence than closer points....<o:p></o:p></p>
<p><o:p> </o:p></p>
<p>The equations used only depend on the distance the points are from each other. NOT the value of any of the points. Though David has a section on how the variogram can be applied to IDS.<o:p></o:p></p>
<p><o:p> </o:p></p>
<p>All the power IDS theory (if there is one) came out of the mining industry in the early 1960's because it was simple.<o:p></o:p></p>
<p><o:p> </o:p></p>
<p>Hope this helps.<o:p></o:p></p>
<p>J.O. Williams<o:p></o:p></p>
<p><o:p> </o:p></p>
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<p class="MsoNormal">On 9/17/19 4:00 AM, Daniel Zepeda Rivas wrote:<o:p></o:p></p>
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<p style="margin-bottom:4.5pt;background:white"><span style="font-size:10.5pt;font-family:"Helvetica",sans-serif;color:#1D2129">When using the Raster -> Analysis -> Grid (Inverse Distance to a Power)<o:p></o:p></span></p>
<p style="mso-margin-top-alt:4.5pt;margin-right:0in;margin-bottom:4.5pt;margin-left:0in;background:white">
<span style="font-size:10.5pt;font-family:"Helvetica",sans-serif;color:#1D2129">At the menu just before pressing run, can somebody please explain me the effect of the "Weighting power" option in the interpolation process?<o:p></o:p></span></p>
<p style="margin-top:4.5pt;background:white"><span style="font-size:10.5pt;font-family:"Helvetica",sans-serif;color:#1D2129">I'm trying to make a temperature map based on points representing each weather station, containing the yearly averages values of temperature,
and when moving the number from the 2 (set it by default) to 4, 6 or 10, the map changes significantly<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<pre>_______________________________________________<o:p></o:p></pre>
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