Hello, I'm following up on this blog post to see if there is a fast way to join points to rasters. http://blog.cleverelephant.ca/2018/09/postgis-external-storage.html
I'm attempting to do a dasymetric mapping process, which is assigning areal unit values to raster pixels. For this example, I have created two tables. Table 1, mn_smokers has are geom (x,y) coordinates and spatial indices on 4326 and 26915. The resulting raster will be stored in mn_dasymetric and it also has indices at 4326 and 26915. When running the explain query it seems that index isn't really being used. CREATE INDEX mn_smokers_gist_4326 ON mn_smokers USING GIST (geom); CREATE INDEX mn_smokers_gist_26915 ON mn_smokers USING GIST (ST_Transform(geom,26915)); CREATE INDEX mn_dasymetric_gist_4326 ON mn_dasymetric USING GIST (ST_Transform(ST_Envelope(rast),4326)); CREATE INDEX mn_dasymetric_gist_26915 ON mn_dasymetric USING GIST (ST_Transform(ST_Envelope(rast),26915)); Type: Nested Loop (Inner); ; Cost: 6.22 - 1594516.11 Type: Limit; ; Cost: 5.11 - 6.22 Type: Nested Loop (Inner); ; Cost: 5.11 - 471.95 Type: Seq Scan; Rel: minnesota_counties ; Cost: 0.00 - 34.09 Type: Bitmap Heap Scan; Rel: mn_smokers ; Cost: 5.11 - 437.50 Type: Bitmap Index Scan; Rel: mn_smokers_gist_4326 ; Cost: 0.00 - 5.10 Type: CTE Scan; Rel: points ; Cost: 0.00 - 4.00 Type: Materialize; ; Cost: 0.00 - 59.57 Type: Seq Scan; Rel: mn_dasymetric ; Cost: 0.00 - 47.38 with points as ( select sp_id as point_id, smoker as point_value, ms.geom from mn_smokers ms inner join minnesota_counties mc on ST_Intersects(ms.geom, mc.geom) ) , point_raster_agg as ( select geom, count(point_id) as pixel_point_value from points group by geom ) , output_rast as ( select r.rid, pixel_point_value, ST_SetValue(rast, ST_Transform(p.geom, 26915), pixel_point_value ) as setrast ,rast, geom from point_raster_agg p inner join mn_dasymetric r on ST_intersects(r.rast, ST_Transform(p.geom, 26915))
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