<html><head></head><body><div style="color:#000; background-color:#fff; font-family:verdana, helvetica, sans-serif;font-size:16px"><div id="yui_3_16_0_1_1445152949648_19212"><span id="yui_3_16_0_1_1445152949648_19214">Not a QGIS (or GRASS) based solution, but GMT (Generic Mapping Tools) has some excellent gridding tools, and for the same price :-)</span></div><div id="yui_3_16_0_1_1445152949648_19298"><span id="yui_3_16_0_1_1445152949648_19214"><br></span></div><div dir="ltr" id="yui_3_16_0_1_1445152949648_19276"><span id="yui_3_16_0_1_1445152949648_19214"> xyz2grd <a id="yui_3_16_0_1_1445152949648_19357" href="http://gmt.soest.hawaii.edu/doc/5.1.0/xyz2grd.html">http://gmt.soest.hawaii.edu/doc/5.1.0/xyz2grd.html</a></span></div><div dir="ltr" id="yui_3_16_0_1_1445152949648_19277"><span id="yui_3_16_0_1_1445152949648_19214">surface (very powerful & configureable) <a id="yui_3_16_0_1_1445152949648_19542" href="http://gmt.soest.hawaii.edu/doc/5.1.0/surface.html">http://gmt.soest.hawaii.edu/doc/5.1.0/surface.html</a><br></span></div><div dir="ltr" id="yui_3_16_0_1_1445152949648_19356"><span id="yui_3_16_0_1_1445152949648_19214">greenspline <a id="yui_3_16_0_1_1445152949648_19609" href="http://gmt.soest.hawaii.edu/doc/5.1.0/greenspline.html">http://gmt.soest.hawaii.edu/doc/5.1.0/greenspline.html</a><br></span></div><div id="yui_3_16_0_1_1445152949648_19474" dir="ltr"><span id="yui_3_16_0_1_1445152949648_19214">triangulate <a id="yui_3_16_0_1_1445152949648_19689" href="http://gmt.soest.hawaii.edu/doc/5.1.0/triangulate.html">http://gmt.soest.hawaii.edu/doc/5.1.0/triangulate.html</a></span></div><div id="yui_3_16_0_1_1445152949648_19851" dir="ltr"><span id="yui_3_16_0_1_1445152949648_19214">sphtriangulate <a id="yui_3_16_0_1_1445152949648_19852" href="http://gmt.soest.hawaii.edu/doc/5.1.0/sphtriangulate.html">http://gmt.soest.hawaii.edu/doc/5.1.0/sphtriangulate.html</a></span></div><div dir="ltr" id="yui_3_16_0_1_1445152949648_19695">nearneighbour <a id="yui_3_16_0_1_1445152949648_19759" href="http://gmt.soest.hawaii.edu/doc/5.1.0/nearneighbor.html">http://gmt.soest.hawaii.edu/doc/5.1.0/nearneighbor.html</a><br></div><div id="yui_3_16_0_1_1445152949648_19757"><br></div><div id="yui_3_16_0_1_1445152949648_19761">Surface in particular - as you increase the surface tension parameter, you will get a model which gets smoother - removing artifacts but also real spikes. Triangulation fits a surface touching each datapoint, with no smoothing, so tends to create ridges or valleys on the lines between points.</div><div id="yui_3_16_0_1_1445152949648_20316"><br></div><div id="yui_3_16_0_1_1445152949648_20317">Whatever tool you use, no one algorithm fits all datasets well, which is why there are so many of them! You may need to experiment with the algorithm (command) and parameters (including grid increment size) which give the "best" result - ie: the one you like most :-)</div><div id="yui_3_16_0_1_1445152949648_20342"><br></div><div id="yui_3_16_0_1_1445152949648_20344">Cheers,</div><div id="yui_3_16_0_1_1445152949648_20345"><br></div><div id="yui_3_16_0_1_1445152949648_20346"> Brent Wood<br> </div><div id="yui_3_16_0_1_1445152949648_19185" style="font-family: verdana, helvetica, sans-serif; font-size: 16px;"> <div id="yui_3_16_0_1_1445152949648_19184" style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div id="yui_3_16_0_1_1445152949648_19183" dir="ltr"> <hr id="yui_3_16_0_1_1445152949648_19211" size="1"> <font id="yui_3_16_0_1_1445152949648_19210" face="Arial" size="2"> <b><span style="font-weight:bold;">From:</span></b> Nicolas Cadieux <nicolas.cadieux@archeotec.ca><br> <b><span style="font-weight: bold;">To:</span></b> qgis-user@lists.osgeo.org <br> <b><span style="font-weight: bold;">Sent:</span></b> Monday, October 19, 2015 4:19 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> Re: [Qgis-user] Removing artifacts in a created DEM<br> </font> </div> <div id="yui_3_16_0_1_1445152949648_19186" class="y_msg_container"><br><div id="yiv4050465564"><div id="yui_3_16_0_1_1445152949648_19187" dir="ltr">Hi,<br>
I would go with the TIN if your points are far apart. That will not create the bumps that you see. IDW is good but you may have to change the IDW weights from 2 (1\2, the typical gravity model) to 3 or 4 to smooth thing out. Be careful and make sure you original values don't shift too much. NN is very good if you have a very high density of sampling points (like LiDAR), at least in regards to the way it is implemented by GDAL.</div>
<div id="yui_3_16_0_1_1445152949648_19190" dir="ltr">Nicolas Cadieux M.Sc.<br>
Les Entreprises Archéotec inc. <br>
8548, rue Saint-Denis Montréal H2P 2H2<br>
Téléphone: 514.381.5112 Fax: 514.381.4995<br>
www.archeotec.ca</div>
<div id="yui_3_16_0_1_1445152949648_19192" class="yiv4050465564gmail_quote">On Oct 17, 2015 03:29, "Andreas Neumann [via OSGeo.org] " <<a href="" rel="nofollow">[hidden email]</a>> wrote:<br><blockquote id="yui_3_16_0_1_1445152949648_19191" style="border-left:2px solid #CCCCCC;padding:0 1em;" class="yiv4050465564quote">
Hi Hernan,<br>
<br>
I think neither of the methods you used give good results for
interpolating terrain data (or most other interpolations).<br>
<br>
I had good results with v.surf.rst (available in the Processing
toolbox in the GRASS section). There are tons of options with the
v.surf.rst - but the defaults probably work for most options. You
also don't have to output all the raster results - just the
interpolated surface.<br>
<br>
One of the other options is the "Interpolation plugin" which comes
with QGIS (but you have to enable it in QGIS). It appears in the
raster menu in as "Interpolation". It offers a TIN interpolation and
IDW. I think the TIN method is the more interesting one.<br>
<br>
Hope this helps,<br>
Andreas<br>
<br>
<div>On 17.10.2015 00:21, hersala wrote:<br>
</div>
<blockquote id="yui_3_16_0_1_1445152949648_19198" style="border-left:2px solid #CCCCCC;padding:0 1em;">
<div id="yui_3_16_0_1_1445152949648_19197" dir="ltr">
<div>Hello,<br>
</div>
<div id="yui_3_16_0_1_1445152949648_19196"><br>
</div>
<div id="yui_3_16_0_1_1445152949648_19199">I'm working with a bundle of N-S and E-W distributed DGPS
point transects on gentle glacier slope. With these points I
created a shp file and then I obtained several DEMs (.tif
files) using the tool Raster/Analysis/Grid (Interpolation).</div>
<div id="yui_3_16_0_1_1445152949648_19200">I've used Nearest Neighbor, Runing Means and Inverse
Distance with several argument values. Inverse Distance
produces the best results, but there are some artifacts that
persists and makes the output unusable. They give the
impression as if the glacial slope has bumps, but on the
contrary, it is quite gentle.</div>
<div id="yui_3_16_0_1_1445152949648_19202"><br>
</div>
<div id="yui_3_16_0_1_1445152949648_19203">Can anyone give any advice in how to proceed to reduce such
artifacts.</div>
<div id="yui_3_16_0_1_1445152949648_19204"><br>
</div>
<div id="yui_3_16_0_1_1445152949648_19205">I'm using QGIS 2.8.2-Wien in MS-Windows.</div>
<div id="yui_3_16_0_1_1445152949648_19206"><br>
</div>
<div>Thanks in advance.</div>
<div><br>
</div>
<div>Hernan</div>
<div><br>
</div>
</div>
<br>
<fieldset></fieldset>
<br>
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