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<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Dear Birgit,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Very many thanks. The query is now running – so it is no longer giving an error. I will not know for a few hours whether it is calculating the necessary values but it seems progress
is being made.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">I have a book coming on SQL – I clearly need to do my homework more thoroughly
</span><span style="font-family:Wingdings;color:#1F497D;mso-fareast-language:EN-US">J</span><span style="color:#1F497D;mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">I will confirm when it stops!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Best wishes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Darrel<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="color:windowtext">From:</span></b><span lang="EN-US" style="color:windowtext"> postgis-users [mailto:postgis-users-bounces@lists.osgeo.org]
<b>On Behalf Of </b>Birgit Laggner<br>
<b>Sent:</b> 24 November 2015 12:19<br>
<b>To:</b> postgis-users@lists.osgeo.org<br>
<b>Subject:</b> Re: [postgis-users] Help with SQL query?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Hi Darrel,<br>
<br>
my PostGIS version is too old for testing, but if I read the documentation right, then your expression has to be SQL. And IF THEN ELSE etc. is not SQL as far as I know - SQL has CASE WHEN.<br>
<br>
So, I would assume, you would need to write your expression like this:<br>
<br>
'CASE WHEN [rast2] > 0.0 THEN [rast1] ELSE NULL END'<br>
<br>
I am curious if this helps with your error...<br>
<br>
Regards,<br>
<br>
Birgit<br>
<br>
<span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal">Am 24.11.2015 um 10:09 schrieb Darrel Maddy:<o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Dear Roxanne,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Many thanks. I did pickup that issue shortly after my last post and it cured the first problem.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">There is still an SQL issue with the expression however.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">I tried ‘IF [rast2]>0.0 THEN [rast1] ELSE NULL ENDIF’</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">This produces an error at $2. I can remove that problem by doing this</span><o:p></o:p></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="color:#1F497D;mso-fareast-language:EN-US">‘IF ([rast2]>0.0) THEN [rast1] ELSE NULL ENDIF’</span></a><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">But then I get the error at THEN</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Curiously ‘[rast2]+[rast1]’ works as intended so somehow the conditional is being specified incorrectly.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Unfortunately there is nothing in the documentation which helps me with this variant.
</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">I will keep trying.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Darrel</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="color:windowtext">From:</span></b><span lang="EN-US" style="color:windowtext"> postgis-users [<a href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>]
<b>On Behalf Of </b>Roxanne Reid-Bennett<br>
<b>Sent:</b> 24 November, 2015 12:46 AM<br>
<b>To:</b> <a href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a><br>
<b>Subject:</b> Re: [postgis-users] Help with SQL query?</span><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
<div>
<p class="MsoNormal">On 11/23/2015 12:41 PM, Darrel Maddy wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Dear Pierre,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">I was not looking for a total solution and I am grateful for the suggestion.
</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Although it may not look like it, I did consult the documentation and also I have Regina’s book beside me. Unfortunately, for me at least, both documents assume some knowledge of SQL
– which I do not have. I am also trying to do this simultaneously with a large number of other things that are new to me. I do not find the errors reported at all informative and consider the query I am trying to perform to be relatively trivial and hence
I had hoped the structure of the query might have been more intuitive. For others it may be.</span><o:p></o:p></p>
</blockquote>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman ,serif",serif"><br>
FWIW - I don't play with rasters, but this appears to be a pure SQL thing... add "as rast" like below and try again.<br>
<br>
<br>
</span><span style="font-size:12.0pt">SELECT ST_MapAlgebra(deposition.rast, concentrated.rast, 'IF concentrated > 6 THEN deposition ELSE NULL ENDIF ' )
<br>
</span><span style="font-size:12.0pt;font-family:"Times New Roman ,serif",serif">as rast</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> FROM mymodel.deposition, mymodel.concentrated</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> WHERE ST_UpperleftX(mymodel.deposition.rast) = ST_UpperleftX(mymodel.concentrated.rast) AND
</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> ST_UpperleftY(mymodel.deposition.rast) = ST_UpperleftY(mymodel.deposition.rast)</span><o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Roxanne<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman ,serif",serif"><br>
<br>
<br>
</span><o:p></o:p></p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">I will try not to bother you again.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US">Darrel</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:EN-US"> </span><o:p></o:p></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> postgis-users [<a href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>]
<b>On Behalf Of </b>Pierre Racine<br>
<b>Sent:</b> 23 November 2015 20:30<br>
<b>To:</b> PostGIS Users Discussion <a href="mailto:postgis-users@lists.osgeo.org">
<postgis-users@lists.osgeo.org></a><br>
<b>Subject:</b> Re: [postgis-users] Help with SQL query?</span><o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">The expression has to stay as it was: 'IF [rast2] > threshold THEN [rast1] ELSE NULL ENDIF '</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Just replace the threshold value as you did.</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Do not try to replace the [rast2] and [rast1]. They refer to the first and second raster pixel values. Read the ST_Mapalgebra doc…</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Don’t expect our suggestions to work blindly. I did not test this query. I’m not in your context. I expect you read the doc about all the mentioned functions and adjust for your specific context.
I said “your query should “look like” this”…</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Pierre</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma",sans-serif">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma",sans-serif"> postgis-users [<a href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>]
<b>On Behalf Of </b>Darrel Maddy<br>
<b>Sent:</b> Monday, November 23, 2015 2:47 PM<br>
<b>To:</b> PostGIS Users Discussion<br>
<b>Subject:</b> Re: [postgis-users] Help with SQL query?</span><o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">OK I spoke too soon.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">I tried this:</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">SELECT (ST_SummaryStats(ST_Union(rast))).sum sum</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">FROM (SELECT ST_MapAlgebra(deposition.rast, concentrated.rast, 'IF concentrated > 6 THEN deposition ELSE NULL ENDIF ' )</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> FROM mymodel.deposition, mymodel.concentrated</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> WHERE ST_UpperleftX(mymodel.deposition.rast) = ST_UpperleftX(mymodel.concentrated.rast) AND
</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> ST_UpperleftY(mymodel.deposition.rast) = ST_UpperleftY(mymodel.deposition.rast) ) foo;</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">And all I get is rast does not exist.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">I’m afraid the penny has not dropped yet
</span><span style="font-family:Wingdings;color:#1F497D">L</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Darrel</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> postgis-users [<a href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>]
<b>On Behalf Of </b>Darrel Maddy<br>
<b>Sent:</b> 23 November 2015 16:30<br>
<b>To:</b> PostGIS Users Discussion <<a href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a>><br>
<b>Subject:</b> Re: [postgis-users] Help with SQL query?</span><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Dear Pierre and Rasmus,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Many thanks for trying to help.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Rasmus: I am aware of GMT but I was looking for a solution in postgis so that I can keep all of the data extraction in one place.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Pierre: That is exactly what I was looking for and very many thanks for including the explanation. I am a little overwhelmed with the number of functions offered in postgis. It is certainly a remarkable tool.
Watching the queries plough through my datasets is a pleasure – albeit the results do not always please me
</span><span style="font-family:Wingdings;color:#1F497D">J</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Hopefully I can put this to work later tonight.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Best wishes</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Darrel</span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> postgis-users [<a href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>]
<b>On Behalf Of </b>Pierre Racine<br>
<b>Sent:</b> 23 November 2015 16:17<br>
<b>To:</b> PostGIS Users Discussion <<a href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a>><br>
<b>Subject:</b> Re: [postgis-users] Help with SQL query?</span><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Darrel,</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt"><span lang="EN-US" style="color:#1F497D">1)</span><span lang="EN-US" style="font-size:7.0pt">
</span><span lang="EN-US" style="color:#1F497D">Create a new raster selecting the right pixels with ST_MapAlgebra(raster, raster)</span><o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt"><span lang="EN-US" style="color:#1F497D">2)</span><span lang="EN-US" style="font-size:7.0pt">
</span><span lang="EN-US" style="color:#1F497D">Make sure only intersecting rasters are processed by using their upper left corner X and Y coordinates (with ST_UpperLeftX() and UpperLeftY())</span><o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt"><span lang="EN-US" style="color:#1F497D">3)</span><span lang="EN-US" style="font-size:7.0pt">
</span><span lang="EN-US" style="color:#1F497D">Sum the selected pixels with ST_SummaryStats(rast)</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">All in all a global query should look like this:</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">SELECT (ST_SummaryStats(ST_Union(rast))).sum sum</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">FFOM (SELECT ST_MapAlgebra(tableA.rast, tableB.rast, 'IF [rast2] > threshold THEN [rast1] ELSE NULL</span><span lang="EN-US"> ENDIF
</span><span lang="EN-US" style="color:#1F497D">' )</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> FROM tableA, tableB</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> WHERE ST_UpperleftX(tableA.rast) = ST_UpperleftX(tableB.rast) AND
</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> ST_UpperleftY(tableA.rast) = ST_UpperleftY(tableB.rast) AND
</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> maybe some other condition here if you get time series e.g. tableA.year = tableB.year AND tableA.month = tableB.month) foo</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">If you have millions of tile you could create indexes on ST_UpperleftX(tableA.rast), ST_UpperleftX(tableB.rast), ST_UpperleftY(tableA.rast) and ST_UpperleftY(tableB.rast) to make the query faster.</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">You could also just use WHERE ST_Intersects(tableA.rast, tableB.rast) instead…</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Pierre</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma",sans-serif">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma",sans-serif"> postgis-users [<a href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>]
<b>On Behalf Of </b>Darrel Maddy<br>
<b>Sent:</b> Monday, November 23, 2015 7:20 AM<br>
<b>To:</b> PostGIS Users Discussion<br>
<b>Subject:</b> [postgis-users] Help with SQL query?</span><o:p></o:p></p>
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<p class="MsoNormal"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal">Dear all,<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">As you know I am relatively new to postgis and SQL and therefore I have much to learn. However, I am facing a paper deadline and need to do some quick analysis of the data I have and I am struggling to figure out how best to pursue what
I need to do.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">I have a significant number of rasters which have double precision values. Without going into detail about what the rasters represent, I need to extract and sum values from one set of rasters in say table A based upon values in another
set of rasters in say table B where the pixel value in the raster from Table B exceeds a threshold. Both tables are the same size (rasters are tiled) but I also need to figure out how I make sure the correct rasters are compared. They have filenames like
this rastervariable_10.tif, rastervariable_100.tif , presumably I need to use a logical expression to strip the numerical value (in this case this represents the year) and then order on that basis?<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">I can do this in QGIS one at a time but that is a little clumsy and rather time consuming.
<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">If someone can just point me in the right direction I am sure I can figure out the rest for myself.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Apologies once more for asking what is probably a rather trivial question and yet again demonstrating my ignorance.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Many thanks<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Darrel<o:p></o:p></p>
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<pre>-- <o:p></o:p></pre>
<pre>[At other schools] I think the most common fault in general is to teach students how to pass exams instead of teaching them the science.<o:p></o:p></pre>
<pre>Donald Knuth<o:p></o:p></pre>
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