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<div class="moz-cite-prefix">On 11/23/2015 12:41 PM, Darrel Maddy
wrote:<br>
</div>
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<p class="MsoNormal"><span
style="color:#1F497D;mso-fareast-language:EN-US">Dear
Pierre,<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 was not
looking for a total solution and I am grateful for the
suggestion.
<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">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></p>
</div>
</blockquote>
<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 style="color:#1F497D">SELECT ST_MapAlgebra(deposition.rast,
concentrated.rast, 'IF concentrated > 6 THEN deposition ELSE
NULL ENDIF ' ) <br>
</span>as rast<br>
<p class="MsoNormal"><span style="color:#1F497D"> FROM
mymodel.deposition, mymodel.concentrated<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"> WHERE
ST_UpperleftX(mymodel.deposition.rast) =
ST_UpperleftX(mymodel.concentrated.rast) AND
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"> ST_UpperleftY(mymodel.deposition.rast)
= ST_UpperleftY(mymodel.deposition.rast)<br>
</span></p>
<p class="MsoNormal"><span style="color:#1F497D"><br>
</span></p>
<p class="MsoNormal">Roxanne</p>
<br>
<blockquote
cite="mid:DB3PR07MB0730E799EBA70B872003E512C1070@DB3PR07MB0730.eurprd07.prod.outlook.com"
type="cite">
<div class="WordSection1">
<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">I will try
not to bother you again.<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>
<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">From:</span></b><span
lang="EN-US"> postgis-users
[<a class="moz-txt-link-freetext" 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 class="moz-txt-link-rfc2396E" href="mailto:postgis-users@lists.osgeo.org"><postgis-users@lists.osgeo.org></a><br>
<b>Subject:</b> Re: [postgis-users] Help with SQL query?<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">The
expression has to stay as it was: 'IF [rast2] > threshold
THEN [rast1] ELSE NULL ENDIF '<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Just
replace the threshold value as you did.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Do
not try to replace the [rast2] and [rast1]. They refer to
the first and second raster pixel values. Read the
ST_Mapalgebra doc…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">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”…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Pierre<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<div style="border:none;border-left:solid blue 1.5pt;padding:0cm
0cm 0cm 4.0pt">
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<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma",sans-serif"
lang="EN-US">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma",sans-serif"
lang="EN-US"> postgis-users [<a moz-do-not-send="true"
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?<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">OK I spoke
too soon.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I tried this:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">SELECT
(ST_SummaryStats(ST_Union(rast))).sum sum<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">FROM (SELECT
ST_MapAlgebra(deposition.rast, concentrated.rast, 'IF
concentrated > 6 THEN deposition ELSE NULL ENDIF ' )<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">
FROM mymodel.deposition, mymodel.concentrated<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">
WHERE ST_UpperleftX(mymodel.deposition.rast) =
ST_UpperleftX(mymodel.concentrated.rast) AND
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"> ST_UpperleftY(mymodel.deposition.rast)
= ST_UpperleftY(mymodel.deposition.rast) ) foo;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">And all I get
is rast does not exist.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></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><span
style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Darrel<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span
lang="EN-US"> postgis-users [<a moz-do-not-send="true"
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
moz-do-not-send="true"
href="mailto:postgis-users@lists.osgeo.org"><a class="moz-txt-link-abbreviated" href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a></a>><br>
<b>Subject:</b> Re: [postgis-users] Help with SQL
query?<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">Dear Pierre
and Rasmus,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Many thanks
for trying to help.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></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><span
style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Hopefully I
can put this to work later tonight.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Best wishes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Darrel<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span
lang="EN-US"> postgis-users [<a moz-do-not-send="true"
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
moz-do-not-send="true"
href="mailto:postgis-users@lists.osgeo.org"><a class="moz-txt-link-abbreviated" href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a></a>><br>
<b>Subject:</b> Re: [postgis-users] Help with SQL
query?<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Darrel,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt"><span
style="color:#1F497D" lang="EN-US">1)</span><span
style="font-size:7.0pt;font-family:"Times New
Roman",serif;color:#1F497D" lang="EN-US">
</span><span style="color:#1F497D" lang="EN-US">Create a new
raster selecting the right pixels with
ST_MapAlgebra(raster, raster)<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt"><span
style="color:#1F497D" lang="EN-US">2)</span><span
style="font-size:7.0pt;font-family:"Times New
Roman",serif;color:#1F497D" lang="EN-US">
</span><span style="color:#1F497D" lang="EN-US">Make sure
only intersecting rasters are processed by using their
upper left corner X and Y coordinates (with
ST_UpperLeftX() and UpperLeftY())<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt"><span
style="color:#1F497D" lang="EN-US">3)</span><span
style="font-size:7.0pt;font-family:"Times New
Roman",serif;color:#1F497D" lang="EN-US">
</span><span style="color:#1F497D" lang="EN-US">Sum the
selected pixels with ST_SummaryStats(rast)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">All
in all a global query should look like this:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">SELECT
(ST_SummaryStats(ST_Union(rast))).sum sum<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">FFOM
(SELECT ST_MapAlgebra(tableA.rast, tableB.rast, 'IF
[rast2] > threshold THEN [rast1] ELSE NULL</span><span
lang="EN-US"> ENDIF
<span style="color:#1F497D">' )<o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
FROM tableA, tableB<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
WHERE ST_UpperleftX(tableA.rast) =
ST_UpperleftX(tableB.rast) AND
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"> ST_UpperleftY(tableA.rast)
= ST_UpperleftY(tableB.rast) AND
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"> maybe
some other condition here if you get time series e.g.
tableA.year = tableB.year AND tableA.month = tableB.month)
foo<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">You
could also just use WHERE ST_Intersects(tableA.rast,
tableB.rast) instead…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Pierre<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma",sans-serif"
lang="EN-US">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma",sans-serif"
lang="EN-US"> postgis-users [<a
moz-do-not-send="true"
href="mailto:postgis-users-bounces@lists.osgeo.org"><a class="moz-txt-link-freetext" href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a></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?<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></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 class="moz-signature" cols="72">--
[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.
Donald Knuth</pre>
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