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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>I think what you are looking for is ST_Union (.. SUM) note this has union types – FIRST, MIN, MAX, COUNT, SUM, MEAN, RANGE<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><a href="http://postgis.net/docs/manual-2.4/RT_ST_Union.html">http://postgis.net/docs/manual-2.4/RT_ST_Union.html</a><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal style='margin-left:.5in'><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> postgis-users [mailto:postgis-users-bounces@lists.osgeo.org] <b>On Behalf Of </b>David M. Kaplan<br><b>Sent:</b> Monday, March 05, 2018 10:03 AM<br><b>To:</b> postgis-users@lists.osgeo.org<br><b>Subject:</b> [postgis-users] Aggregating rasters by adding and other confusions<o:p></o:p></span></p></div></div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p><div><p class=MsoNormal style='margin-left:.5in'>Hi,<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>I have recently started working with the postgis raster functionality. In general, I have found this really useful and have been able to do some neat things fairly simply with this raster functionality. Nevertheless, there are a few basic things that I am confused about and I was hoping someone could give me a hand.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>(1) First of all, I have a table with a bunch of rasters that have the same extent, alignment, scale, etc. and I want to aggregate them together into a single raster using pixel-by-pixel addition. It seems like there should be a function to do this, but I can't find one. Is there an aggregate "ST_MapAlgebra" function? <o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Given that I couldn't find one, I defined an aggregate function as follows:<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><pre style='margin-left:.5in'>CREATE OR REPLACE FUNCTION AddRasters(r1 raster, r2 raster)<o:p></o:p></pre><pre style='margin-left:.5in'> RETURNS raster AS<o:p></o:p></pre><pre style='margin-left:.5in'>$BODY$<o:p></o:p></pre><pre style='margin-left:.5in'>SELECT ST_MapAlgebra($1,$2,'[rast1]+[rast2]');<o:p></o:p></pre><pre style='margin-left:.5in'>$BODY$ LANGUAGE 'sql' IMMUTABLE STRICT;<o:p></o:p></pre><pre style='margin-left:.5in'><o:p> </o:p></pre><pre style='margin-left:.5in'>CREATE AGGREGATE sum (raster)<o:p></o:p></pre><pre style='margin-left:.5in'>(<o:p></o:p></pre><pre style='margin-left:.5in'> sfunc = AddRasters,<o:p></o:p></pre><pre style='margin-left:.5in'> stype = raster<o:p></o:p></pre><pre style='margin-left:.5in'>);<o:p></o:p></pre><pre style='margin-left:.5in'><o:p> </o:p></pre><div><p class=MsoNormal style='margin-left:.5in'>(2) This seems to work, but it has the unexpected behavior that it replaces 0 values with NULL. In my case, this is fine, but I am wondering why it does this? I can't find anything that indicates that it should be replacing zeros with NULL. Here is the metadata associated with one of my rasters (the others are similar):<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><pre style='margin-left:.5in'># SELECT ST_BandMetadata(rast), ST_Metadata(rast), ST_SummaryStats(rast) FROM blah;<o:p></o:p></pre><pre style='margin-left:.5in'>-[ RECORD 1 ]---+-------------------------------------------------------<o:p></o:p></pre><pre style='margin-left:.5in'>st_bandmetadata | (16BUI,,f,)<o:p></o:p></pre><pre style='margin-left:.5in'>st_metadata | (-180,90,360,180,1,-1,0,0,4326,1)<o:p></o:p></pre><pre style='margin-left:.5in'>st_summarystats | (64800,417,0.00643518518518519,0.223617719977485,0,46)<o:p></o:p></pre><pre style='margin-left:.5in'><o:p> </o:p></pre><div><p class=MsoNormal style='margin-left:.5in'>I have not defined a nodataval for these layers and the original layers have no NULL values.<o:p></o:p></p></div><pre style='margin-left:.5in'><o:p> </o:p></pre><div><p class=MsoNormal style='margin-left:.5in'>(3) Is there a postgis command to turn all the NULL values back into zeros?<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>(4) I was also considering just defining the '+' operator for raster + raster to be pixel-by-pixel addition. Is there any reason that I wouldn't want to do this?<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>(5) Finally, I have been visualizing results with QGIS using the DB Manager. However, I don't see how to select a row from a raster table and incorporate just that row into the canvas. Is there a way to do this?<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Thanks for the assistance,<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>David<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><pre style='margin-left:.5in'>-- <o:p></o:p></pre><div><p class=MsoNormal style='margin-left:.5in'>**********************************<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>David M. Kaplan<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Charge de Recherche 1<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Institut de Recherche pour le Developpement (IRD)<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>UMR MARBEC (IRD/Ifremer/CNRS/UMII)<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>av. Jean Monnet<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>CS 30171<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>34203 Sete cedex<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>France<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Email: <a href="mailto:david.kaplan@ird.fr">david.kaplan@ird.fr</a><o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Phone: +33 (0)4 99 57 32 25<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Fax: +33 (0)4 99 57 32 95<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><a href="http://www.umr-marbec.fr/kaplan-david.html">http://www.umr-marbec.fr/kaplan-david.html</a><o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><a href="http://www.davidmkaplan.fr/">http://www.davidmkaplan.fr/</a><o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>**********************************<o:p></o:p></p></div></div></div></body></html>