<div dir="ltr">Hello Cesar<div><br></div><div>I wouldn't expect pixel resolution to play a role here. The statistics must be carried out over the values. </div><div>The raster(s) I'm testing are rectangular, without null values. So reprojecting will change the pixel size (from a square to a rectangle), but it will (should) not change the number of pixels.</div><div><br></div><div>I'll try in another GRASS version and post the results.</div><div><br></div><div>best</div><div><br></div><div>Carlos</div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Nov 16, 2015 at 4:48 PM, César Augusto Ramírez Franco <span dir="ltr"><<a href="mailto:caesarivs@gmail.com" target="_blank">caesarivs@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">Hello Carlos,</p>
<p dir="ltr">Maybe it has something to do with the pixel resolution? I would certainly expect the same results, but with a very similar region (i.e. same number of rows and columns, or at least very close and a similar number of pixels)</p>
<p dir="ltr">Maybe when projecting the raster, the length of the array is varying but I wouldn't expect to vary very much, are you getting the same results in a previous version of GRASS? (7.0 or even 6.4?)</p>
<p dir="ltr">Greetings</p>
<div class="gmail_quote"><div><div class="h5">El nov. 16, 2015 11:35 AM, "Carlos Grohmann" <<a href="mailto:carlos.grohmann@gmail.com" target="_blank">carlos.grohmann@gmail.com</a>> escribió:<br type="attribution"></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5"><div dir="ltr">Hi all.<div><br></div><div>I'm analyzing some global-scale DEMs, like ETOPO1/2, SRTM30_PLUS, etc.</div><div><br></div><div>I'm getting the statistics for the whole dataset with r.univar, but today I noticed that the results differ if I use different projections. (GRASS 7.1)</div><div><br></div><div>For example, ETOPO2:</div><div><br></div><div>Using a latlong pseudo-projection (plate carré)</div><div><br></div><div><br></div><div>min:<span style="white-space:pre-wrap"> </span><span style="white-space:pre-wrap"> </span>-10791<span style="white-space:pre-wrap"> </span></div><div>max:<span style="white-space:pre-wrap"> </span>8440</div><div>mean:<span style="white-space:pre-wrap"> </span>-<a href="tel:1888.6480792" value="+18886480792" target="_blank">1888.6480792</a></div><div>median:<span style="white-space:pre-wrap"> </span>-2457<span style="white-space:pre-wrap"> </span></div><div>stddev:<span style="white-space:pre-wrap"> </span>2650.01922839<span style="white-space:pre-wrap"> </span></div><div>p25:<span style="white-space:pre-wrap"> </span><span style="white-space:pre-wrap"> </span>-4273</div><div>p75:<span style="white-space:pre-wrap"> </span><span style="white-space:pre-wrap"> </span>216<span style="white-space:pre-wrap"> </span></div><div><br></div><div><br></div><div><div>And using equal-area cylindrical:</div><div><br></div><div>min:<span style="white-space:pre-wrap"> </span><span style="white-space:pre-wrap"> </span>-10791<span style="white-space:pre-wrap"> </span></div><div>max:<span style="white-space:pre-wrap"> </span>8440</div><div>mean:<span style="white-space:pre-wrap"> </span>-2379.78247747 </div><div>median:<span style="white-space:pre-wrap"> </span>-3291 <span style="white-space:pre-wrap"> </span></div><div>stddev:<span style="white-space:pre-wrap"> </span>2507.89668617 </div><div>p25:<span style="white-space:pre-wrap"> </span><span style="white-space:pre-wrap"> </span>-4541</div><div>p75:<span style="white-space:pre-wrap"> </span><span style="white-space:pre-wrap"> </span>94<span style="white-space:pre-wrap"> </span></div><div><br></div></div><div><br></div><div><br></div><div>Are these differences expected? I would think that they should be the same, regardless of projection (I'm thinking on the elevation values as an array of values). </div><div><br></div><div>thanks</div><div><br></div><div>Carlos</div><div><br></div><div><br></div><div><br></div><div><br clear="all"><div><br></div>-- <br><div><div dir="ltr">Prof. Carlos Henrique Grohmann<br>Institute of Energy and Environment - Univ. of São Paulo, Brazil<div>- Digital Terrain Analysis | GIS | Remote Sensing - </div><div><br></div><div><a href="http://carlosgrohmann.com/" target="_blank">http://carlosgrohmann.com</a></div><div><a href="http://orcid.org/0000-0001-5073-5572" style="font-size:13px;color:rgb(17,85,204);font-family:arial,sans-serif;background-color:rgb(255,255,255)" target="_blank">http://orcid.org/0000-0001-5073-5572</a><br><div>________________<br>Can’t stop the signal.</div></div></div></div>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div dir="ltr">Prof. Carlos Henrique Grohmann<br>Institute of Energy and Environment - Univ. of São Paulo, Brazil<div>- Digital Terrain Analysis | GIS | Remote Sensing - </div><div><br></div><div><a href="http://carlosgrohmann.com/" target="_blank">http://carlosgrohmann.com</a></div><div><a href="http://orcid.org/0000-0001-5073-5572" style="font-size:13px;color:rgb(17,85,204);font-family:arial,sans-serif;background-color:rgb(255,255,255)" target="_blank">http://orcid.org/0000-0001-5073-5572</a><br><div>________________<br>Can’t stop the signal.</div></div></div></div>
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