Good day.<div><br></div><div>I am doing some benchmarking trying to find out the most optimal way to calculate vegetation indexes. For example I am calculating NDVI index where the size of NIR and RED bands are 2.2 GB each and I get the following results on same hardware.</div>
<div><br></div><div><ul><li>using <a href="http://i.vi" target="_blank">i.vi</a> </li></ul>Calculation takes <font color="#cc0000">14m 24s</font></div><div><br></div><div><ul><li>using r.mapcalc (it is compiled with --with-pthread option)</li>
</ul>Calculation takes <font color="#cc0000">6m 30s</font> (<b>huge difference - same result!!!</b>)</div><div><br></div><div><ul><li>using i.vi.mpi within 1 node with 8 cores</li></ul>Number of CPU | Calculation time</div>
<div>2 CPU | <font color="#cc0000">12m 14s</font></div><div>3 CPU | <font color="#cc0000">12m 8s</font></div><div>4 CPU | <font color="#cc0000">11m 59s</font></div>
<div><font color="#cc0000"><br></font></div><div>And when I am trying to submit this job on cluster, on a several nods (e.g. 6 nods with 8 CPU on each - 48 CPU), I am getting <b>VERY BAD</b> result - <font color="#cc0000">more than 90 minutes</font> , for a calculation which r.mapcalc did in just <font color="#cc0000">6m30s.</font></div>
<div><font color="#cc0000"><br></font></div><div>So now I really cannot understand the meaning of <a href="http://i.vi">i.vi</a> or i.vi.mpi.</div><div><br></div><div>Can anyone explain, what purposes these modules developed for? Which kind of tasks they do better than r.mapcalc? What can I try to see the usefulness of <a href="http://i.vi">i.vi</a> or i.vi.mpi?</div>
<div>Where can I find some documentation explaining the inner structure of these modules and understand the differences between <a href="http://i.vi">i.vi</a> and r.mapcalc (because actually, as I found out, r.mapcalc can do everything that <a href="http://i.vi">i.vi</a> do, but more that 2 times faster.) ?</div>
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