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<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">Hey
everyone,</span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">I am writing
my Bachelor Thesis on going for a case study to check out performance and
usability of the new Postgis raster module for storing huge amount of climate
data.</span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">The data is
stored in alpha-numeric data in postgres tables at the moment. My task is to
create PostGIS-rasters from this data. Therefor I created empty rasters of 650
x 860 pixels and used following statement to update raster cells with value
from the original data:</span><br/></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">UPDATE
target_tbl SET rast = ST_SetValue(rast, 1, COL, ROW, CLIMATE_VALUE) WHERE EXTRACT(DOY
FROM datum) = CURRENT_DAY;</span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">The problem
is that updating each cell, using the ST_SetValue-function takes too much time.
See list below:</span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB"> </span></p>
<p class="MsoNormal">10 updates: </p>
<p class="MsoNormal">2.451 ms = 2,4 sek</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">100 updates:</p>
<p class="MsoNormal">22.468 ms = 22,4 sek</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">1000 updates:</p>
<p class="MsoNormal">226.671 ms = 226,7 sek = ca. 3,8 min</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">10000 updates:</p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">2.269.674
ms = 2.269 sek = ca. 38 min</span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">To generate
rasters from the complete original data I would have to run about 295 billion
updates. So… this would simple take too much time!!! ;)</span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">Now, my
question! </span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">Is there
any other way to create rasters from the original data than updating an empty
raster cell by cell? </span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB"> </span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">I really
would appreciate your help and ideas.</span></p>
<p class="MsoNormal"><span lang="EN-GB" style="mso-ansi-language:EN-GB">Daniel</span></p>
</div><div><br/></div></div> <br><br><table cellpadding="0" cellspacing="0" border="0"><tr><td style="font-family:verdana; font-size:12px; line-height:17px;border-top:1px solid #000000">SMS schreiben mit WEB.DE FreeMail - einfach, schnell und <br>kostenguenstig. Jetzt gleich testen! <a href="http://f.web.de/?mc=021192"><b>http://f.web.de/?mc=021192</b></a></td></tr></table>
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