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--></style></head><body bgcolor=white lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'>Hi Rémi,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'>Thanks for the suggestion. I tiled the raster and added a ST_Intersects, and the whole operation finished in just a couple of minutes (the previous version hadn’t completed when I left it running overnight). The command I used was this:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'>UPDATE hourly_positions hp SET landform = <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'> (SELECT ST_Value(rast,hp.geom4326) FROM landforms4326_128 lf where (lf.rast && hp.geom4326) AND ST_Intersects(lf.rast,hp.geom4326))<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'>So, I don’t mean to sound critical of PostGIS, because I love the program and I have the utmost respect for everyone who works on it, but it appears to me that ST_Value is a “dumb” function; i.e., it doesn’t know how to find pixels in a raster with any reasonable speed. Is there any technical reason that its speed couldn’t be improved? As I mentioned in my original question, this operation (finding pixel values at many individual points) is commonly needed for certain classes of problems.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'>Thanks again for saving my bacon!<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'>John<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:Calibri'><o:p> </o:p></span></p><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-family:Calibri;color:black'>From: </span></b><span style='font-family:Calibri;color:black'>postgis-users <postgis-users-bounces@lists.osgeo.org> on behalf of Rémi Cura <remi.cura@gmail.com><br><b>Reply-To: </b>PostGIS Users Discussion <postgis-users@lists.osgeo.org><br><b>Date: </b>Saturday, February 4, 2017 at 3:01 AM<br><b>To: </b>PostGIS Users Discussion <postgis-users@lists.osgeo.org><br><b>Subject: </b>Re: [postgis-users] ST_value slow<o:p></o:p></span></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><div><p class=MsoNormal><span style='font-family:Courier'>Hey,<o:p></o:p></span></p></div><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-family:Courier'>I suppose your raster is correctly cut into small pieces.<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:Courier'>You should first try to clock one point value retrieval.<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:Courier'>It should be < 50ms (or you have an index issue)<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:Courier'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-family:Courier'>Then you could force the use of index by writting a function <br>update_one_point(point) $$ update XXX set XXX WHERE ST_Intersects(rast,point);$$<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:Courier'><o:p> </o:p></span></p></div><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-family:Courier'>You would then call your function on all points:<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:Courier'>SELECT update_one_point(hp.geom4326)<o:p></o:p></span></p></div><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-family:Courier'>FROM hp<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:Courier'>Cheers<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:Courier'>Rémi-C<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-family:Courier'> <o:p></o:p></span></p></div></div><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>2017-02-04 6:44 GMT+01:00 J Payne <<a href="mailto:jcpayne@uw.edu" target="_blank">jcpayne@uw.edu</a>>:<o:p></o:p></p><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in'><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt'>Hello. I have an animal track that wanders around on a landscape, and I want to extract the pixel values for each location on the track. This kind of operation is very common for animal studies. The landscape is represented by a one-row raster map (“landforms4326”), and the GPS positions are in a table called “hourly_positions”. I am using a recent version of PostGIS and a very simple query to find the pixel values:</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt'>UPDATE hourly_positions hp SET landform = (SELECT ST_Value(rast,hp.geom4326) FROM landforms4326)</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt'>I have about 450,000 points, and both the landscape raster and the point geometries are indexed. For some reason, the operation is *<b>incredibly</b>* slow (it’s already been running for more than 8 hours on a nearly new Macbook Pro, and still isn’t finished). Am I missing something? I can’t for the life of me imagine why it would be so slow, since PostGIS is very fast with all sorts of other operations on the same data (intersections, etc.).</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt'>Thanks,</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt'>John</span><o:p></o:p></p></div></div><p class=MsoNormal><br>_______________________________________________<br>postgis-users mailing list<br><a href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a><br><a href="https://lists.osgeo.org/mailman/listinfo/postgis-users" target="_blank">https://lists.osgeo.org/mailman/listinfo/postgis-users</a><o:p></o:p></p></blockquote></div><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal>_______________________________________________ postgis-users mailing list postgis-users@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/postgis-users<o:p></o:p></p></div></body></html>