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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>ST_Resize might be a better option<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'><a href="https://postgis.net/docs/RT_ST_Resize.html">https://postgis.net/docs/RT_ST_Resize.html</a><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'>ST_Resize takes in raster width/height similar to ST_Resample.<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 style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> Regina Obe [mailto:lr@pcorp.us] <br><b>Sent:</b> Tuesday, December 6, 2022 2:53 PM<br><b>To:</b> 'PostGIS Users Discussion' <postgis-users@lists.osgeo.org><br><b>Cc:</b> 'liglio.pessoal@nexxa.com.br' <liglio.pessoal@nexxa.com.br><br><b>Subject:</b> RE: [postgis-users] RES: Clipping a raster and a polygon using ST_Intersection<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='color:#1F497D'>> </span>Each pixel is associated with a value in the original raster, and when you do resample, what value is associated to the pixels (in the docs “New pixel values are computed using the NearestNeighbor”). <o:p></o:p></p><p class=MsoNormal>So in your example x5, only one pixel has the original pixel value and the others 24 pixels has zero or nodata ? If I do colored scale of values it not seems right.<o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Hmm that is not what I was expecting. Then again I always use the function to reduce resolution, and not for this particular purpose. I had assumed it would apply the value to the next neighboring and keep on applying that way. But sounds like I was wrong about that.<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 think I was confusing that with ST_Rescale. Try using ST_Rescale instead and see if that gives expected results.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Note ST_Rescale takes as input pixel sizes. In your case you want to reduce the size of each pixel. The below reduces the pixel size by 20%<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'><a href="https://postgis.net/docs/RT_ST_Rescale.html">https://postgis.net/docs/RT_ST_Rescale.html</a><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal>SELECT ST_Clip( <span style='color:#1F497D'>ST_Rescale(rast, ST_PixelWidth(rast)*0.2, ST_PixelHeight(rast)*0.2 ) , c.</span> area_country<span style='color:#1F497D'>) <o:p></o:p></span></p><p class=MsoNormal style='text-indent:.5in'>FROM country AS c<o:p></o:p></p><p class=MsoNormal style='margin-left:.5in;text-indent:.5in'>INNER JOIN tb_densitysurface AS d <o:p></o:p></p><p class=MsoNormal style='margin-left:1.0in;text-indent:.5in'>ON ( ST_Intersects(d.rast, c.area_country) )<o:p></o:p></p><p class=MsoNormal>WHERE c.gid = 19<span lang=PT-BR>;</span><o:p></o:p></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>Another question: I do a retangular matrix larger than the country (creating an empty raster and dumping each pixel as polygon, and counting lightining inside each sqare). So I have a lot of squares to compute, and 20 years of lightining (about 2 billions). <o:p></o:p></p><p class=MsoNormal>It will be more efficient/faster if my empty raster has the shape of my country, so It will have less squares to compute. It is possible ?<o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Yes it would be more efficient both in space and time for computing. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Just clip your raster by the country boundaries kind of like you were doing.<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'>So something like<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'>CREATE TABLE </span>tb_densitysurface _country_clip AS <o:p></o:p></p><p class=MsoNormal>SELECT s.rid, ST_Clip(s.rast, geom) AS rast<o:p></o:p></p><p class=MsoNormal>FROM tb_densitysurface AS s CROSS JOIN (SELECT ST_Union(area_country) AS geom FROM country_boundaries) AS c;<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I recall you said you had just one raster, if you have multiple, then you should change the above an INNER JOIN <o:p></o:p></p><p class=MsoNormal>ST_Intersects(s.rast, c.geom). If you only care about one country, you can clip to that one country.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The only reason I am unioning is so you don’t end up with duplicate rasters at country boundaries.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Hope that helps,<o:p></o:p></p><p class=MsoNormal>Regina <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 style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> <a href="mailto:liglio.pessoal@nexxa.com.br">liglio.pessoal@nexxa.com.br</a> [<a href="mailto:liglio.pessoal@nexxa.com.br">mailto:liglio.pessoal@nexxa.com.br</a>] <br><b>Sent:</b> Tuesday, December 6, 2022 2:20 PM<br><b>To:</b> 'Regina Obe' <<a href="mailto:lr@pcorp.us">lr@pcorp.us</a>><br><b>Subject:</b> RES: [postgis-users] RES: Clipping a raster and a polygon using ST_Intersection<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=PT-BR>Regina,<o:p></o:p></span></p><p class=MsoNormal><span lang=PT-BR><o:p> </o:p></span></p><p class=MsoNormal>Thank you very much for your reply, and by the way congratulations for your book “PostGis in action” third edition, I bought and it is very good.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='color:#1F497D'>Just occurred to me that the ST_Intersection I gave you earlier probably does much the same as ST_Clip</span><o:p></o:p></p><p class=MsoNormal>R: Yes is pretty much the same. The result image is the same.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Each pixel is associated with a value in the original raster, and when you do resample, what value is associated to the pixels (in the docs “New pixel values are computed using the NearestNeighbor”). <o:p></o:p></p><p class=MsoNormal>So in your example x5, only one pixel has the original pixel value and the others 24 pixels has zero or nodata ? If I do colored scale of values it not seems right.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Another question: I do a retangular matrix larger than the country (creating an empty raster and dumping each pixel as polygon, and counting lightining inside each sqare). So I have a lot of squares to compute, and 20 years of lightining (about 2 billions). <o:p></o:p></p><p class=MsoNormal>It will be more efficient/faster if my empty raster has the shape of my country, so It will have less squares to compute. It is possible ?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>Regards,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=PT-BR>Liglio<o:p></o:p></span></p></div><p class=MsoNormal><span lang=PT-BR><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><b><span lang=PT-BR>De:</span></b><span lang=PT-BR> Regina Obe <<a href="mailto:lr@pcorp.us">lr@pcorp.us</a>> <br><b>Enviada em:</b> segunda-feira, 5 de dezembro de 2022 13:25<br><b>Para:</b> 'PostGIS Users Discussion' <<a href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a>><br><b>Cc:</b> <a href="mailto:liglio.pessoal@nexxa.com.br">liglio.pessoal@nexxa.com.br</a><br><b>Assunto:</b> RE: [postgis-users] RES: Clipping a raster and a polygon using ST_Intersection<o:p></o:p></span></p></div></div><p class=MsoNormal><span lang=PT-BR><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Just occurred to me that the ST_Intersection I gave you earlier probably does much the same as ST_Clip.<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'>That said, you should be able to achieve a less choppy result using ST_Resample and ST_Clip in unison.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Increase the 5 to as much as you need to get the less choppy effect you are looking for.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal>SELECT ST_Clip( <span style='color:#1F497D'>ST_Resample(rast, ST_Width(rast)*5, ST_Height(rast)*5 ) , c.</span> area_country<span style='color:#1F497D'>) <o:p></o:p></span></p><p class=MsoNormal style='text-indent:.5in'>FROM country AS c<o:p></o:p></p><p class=MsoNormal style='margin-left:.5in;text-indent:.5in'>INNER JOIN tb_densitysurface AS d <o:p></o:p></p><p class=MsoNormal style='margin-left:1.0in;text-indent:.5in'>ON ( ST_Intersects(d.rast, c.area_country) )<o:p></o:p></p><p class=MsoNormal>WHERE c.gid = 19<span lang=PT-BR>;</span><o:p></o:p></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 style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> Regina Obe [<a href="mailto:lr@pcorp.us">mailto:lr@pcorp.us</a>] <br><b>Sent:</b> Sunday, December 4, 2022 12:10 PM<br><b>To:</b> 'PostGIS Users Discussion' <<a href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a>><br><b>Cc:</b> 'liglio.pessoal@nexxa.com.br' <<a href="mailto:liglio.pessoal@nexxa.com.br">liglio.pessoal@nexxa.com.br</a>><br><b>Subject:</b> RE: [postgis-users] RES: Clipping a raster and a polygon using ST_Intersection<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='color:#1F497D'>Liglio,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>b1 being choppier than b2, is because the rasterized polygon takes on the pixel size of your low res polygon.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I’d try resampling your </span>tb_densitysurface to lower pixel size before you do the operation with ST_Resample.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='color:#1F497D'><a href="https://postgis.net/docs/RT_ST_Resample.html">https://postgis.net/docs/RT_ST_Resample.html</a><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'>The width and height are measured in pixels. The idea is you want your tb_densitysurface to have more pixels than it does now so that the size of each pixel is smaller.<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'>If you do something like <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'>CREATE TABLE tb_densitysurface_x5 AS <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>SELECT rid, ST_Resample(rast, ST_Width(rast)*5, ST_Height(rast)*5 ) AS rast<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>FROM tb_densitysurface;<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'>That should give you the same spatial ref sys, but the pixels will be smaller in size.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>You can then use this to rerun the ST_Intersection in raster space. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I think it will be a little slower though, because the more pixels you have the slower things get.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Just keep on increasing that number 5 until you get something that meets your choppiness criteria.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>As you get less choppy, operations will get slower, so you need to find a sweet spot there.<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'>Regarding: </span>There is a way to export this image and associate a value for each square (polygon) to be colored accordingly ?<o:p></o:p></p><p class=MsoNormal>Was that to resolve the above issue, or you just want to know.<o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Well there is ST_PixelAsPolygons which will convert each pixel to a square polygon. <a href="https://postgis.net/docs/RT_ST_PixelAsPolygons.html">https://postgis.net/docs/RT_ST_PixelAsPolygons.html</a><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'>There is also ST_DumpAsPolygons <a href="https://postgis.net/docs/RT_ST_DumpAsPolygons.html">https://postgis.net/docs/RT_ST_DumpAsPolygons.html</a> which tries to aggregate nearby pixels with the same value into a polygon.<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'>Both return geomval rows similar to the ST_Intersection of raster, geom. As I recall I think those were completely rewritten in C so should still be faster than ST_Intersection(geometry,raster).<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> postgis-users [<a href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>] <b>On Behalf Of </b><a href="mailto:liglio.pessoal@nexxa.com.br">liglio.pessoal@nexxa.com.br</a><br><b>Sent:</b> Wednesday, November 30, 2022 9:37 AM<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> [postgis-users] RES: Clipping a raster and a polygon using ST_Intersection<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=PT-BR>Regina,<o:p></o:p></span></p><p class=MsoNormal><span lang=PT-BR><o:p> </o:p></span></p><p class=MsoNormal>Thanks for your replay. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Your solution is fast like using ST_Clip, but I still have the problem that my pixels are 25km square (low definition) and the image look like this: (image b1.jpg)<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>And I want to produce something like this: (image b2.jpg)<o:p></o:p></p><p class=MsoNormal><b><o:p> </o:p></b></p><p class=MsoNormal>I know that the second image cannot be reproduced as just raster with big pixels, the pixels cannot be cutted.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>There is a way to export this image and associate a value for each square (polygon) to be colored accordingly ?<o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Regards,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Liglio<o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span lang=PT-BR>De:</span></b><span lang=PT-BR> postgis-users <<a href="mailto:postgis-users-bounces@lists.osgeo.org">postgis-users-bounces@lists.osgeo.org</a>> <b>Em nome de </b>Regina Obe<br><b>Enviada em:</b> quinta-feira, 24 de novembro de 2022 12:19<br><b>Para:</b> 'PostGIS Users Discussion' <<a href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a>><br><b>Assunto:</b> Re: [postgis-users] Clipping a raster and a polygon using ST_Intersection<o:p></o:p></span></p></div></div><p class=MsoNormal><span lang=PT-BR><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I’m not quite sure what you mean by edges aren’t smooth. Rasters are never really smooth. Vectors are smooth. Rasters may look smooth at the edges, but that’s more because pixels are square and the pixels in each tile line up with the pixels.<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'>If you want it to look a little smoother, maybe expand your envelop ever so slightly so it lines up with a pixel in a raster. So each edge pixel is guaranteed to be fully inside the raster and no edge partly outside the raster or do the operation in raster space which I will explain shortly.<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'>ST_Intersection yes is known to be very slow and as you noticed does not give you a raster back. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Is ST_Clip + ST_Intersects performance sufficient for your needs? <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'>ST_Clip really is ST_Intersection in raster space for raster/geometry. So you could do the intersection in pure raster space by converting your geometry to a raster (making sure to align your new raster with your reference raster). That should make the edges smooth.<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'>Like so – not tested so might have some syntax errors and also I haven’t used this in a very long time so may be wrong about what it returns.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal> SELECT ST_Intersection(r.rast, r2.rast) AS new_rast<o:p></o:p></p><p class=MsoNormal> FROM tb_densitysurface AS r, country, <o:p></o:p></p><p class=MsoNormal>-- create a raster to represent the country that has the same alignment as our density raster (pixels use the same grid)<o:p></o:p></p><p class=MsoNormal> ST_AsRaster( country.area_country, r.rast, <var><span style='font-family:"Calibri",sans-serif'>'1BB', 0</span></var>) AS r2(rast)<o:p></o:p></p><p class=MsoNormal> WHERE country.gid = 19 AND ST_Intersects(r.rast, r2.rast) <o:p></o:p></p><p class=MsoNormal><span lang=PT-BR>) As 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'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>As far as tiling goes, yah that would improve the smoothness of the inner tiles but not most outer ones.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>You’d also need to ST_Union them all up to get back to a single tile which will add perhaps more overhead than just keeping as single tile.<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'>If you want to tile your raster, you can use this function - <a href="https://postgis.net/docs/manual-2.5/RT_ST_Tile.html">https://postgis.net/docs/manual-2.5/RT_ST_Tile.html</a><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'>Hope that helps,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Regina<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><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> postgis-users [<a href="mailto:postgis-users-bounces@lists.osgeo.org">mailto:postgis-users-bounces@lists.osgeo.org</a>] <b>On Behalf Of </b><a href="mailto:liglio.pessoal@nexxa.com.br">liglio.pessoal@nexxa.com.br</a><br><b>Sent:</b> Tuesday, November 22, 2022 2:00 PM<br><b>To:</b> <a href="mailto:postgis-users@lists.osgeo.org">postgis-users@lists.osgeo.org</a><br><b>Subject:</b> [postgis-users] Clipping a raster and a polygon using ST_Intersection<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Hi,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I created a retangular raster representing number of lightnings in a square. So I have this matrix raster created using ST_MapAlgebraFct and ST_MakeEmptyRaster. <o:p></o:p></p><p class=MsoNormal>This raster is not a tiled raster (tb_densitysurface), and when I Clip this raster using a polygon, the query below, the performance is not good.<o:p></o:p></p><p class=MsoNormal>Maybe because the raster is not tiled. So how do I tile this raster ? And I want the result to be a raster (not gval) to be exported as a file, and then colored using GDAL.<o:p></o:p></p><p class=MsoNormal>It worked with a different query only using ST_Clip (this returns a rast column and is very fast), but the edges arenīt smooth as using ST_Insersection. I am using Postgis 2.5.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>SELECT<o:p></o:p></p><p class=MsoNormal> (gval).val<o:p></o:p></p><p class=MsoNormal> (gval).geom<o:p></o:p></p><p class=MsoNormal>FROM (<o:p></o:p></p><p class=MsoNormal> SELECT ST_Intersection(<o:p></o:p></p><p class=MsoNormal> ST_Clip(rast,ST_Envelope(area_country)),<o:p></o:p></p><p class=MsoNormal> 1,<o:p></o:p></p><p class=MsoNormal> area_country<o:p></o:p></p><p class=MsoNormal> ) As gval<o:p></o:p></p><p class=MsoNormal> FROM country, tb_densitysurface WHERE ST_Intersects(rast, area_country) and country.gid = 19<o:p></o:p></p><p class=MsoNormal><span lang=PT-BR>) As foo<o:p></o:p></span></p><p class=MsoNormal><span lang=PT-BR><o:p> </o:p></span></p><p class=MsoNormal><span lang=PT-BR><o:p> </o:p></span></p><p class=MsoNormal><span lang=PT-BR>Regards,<o:p></o:p></span></p><p class=MsoNormal><span lang=PT-BR><o:p> </o:p></span></p><p class=MsoNormal><span lang=PT-BR>Liglio<o:p></o:p></span></p><p class=MsoNormal><span lang=PT-BR><o:p> </o:p></span></p></div></div></div></div></div></div></body></html>