<div dir="ltr"><div>Thanks, Florian,</div><div><br></div><div>Both of those alternatives take ~1 min 20 sec.</div><div><br></div><div>Below are the execution plans for the queries I previously shared. Let me know if there's anything else that would be helpful.</div><div><br></div><div>Best,</div><div>Mike<br></div><div><br></div><div>------Raster/Vector Overlay<br></div><div>explain select<br>(foo.geomval).val,<br>sum(st_area((geomval).geom)) as area_ft2<br>from (<br> select (st_intersection(a.rast, b.geom_2263)) as geomval<br> from base_rasters.landcover6in_2017 a<br> join scratch.smallsample b<br> on st_intersects(a.rast, b.geom_2263)) as foo<br>group by val;</div><div><br></div><div>HashAggregate (cost=3904551.46..3904553.46 rows=200 width=16)<br> Group Key: (foo.geomval).val<br> -> Subquery Scan on foo (cost=0.41..456301.46 rows=26525000 width=40)<br> -> ProjectSet (cost=0.41..191051.46 rows=26525000 width=32)<br> -> Nested Loop (cost=0.41..51662.59 rows=26525 width=803)<br> -> Seq Scan on smallsample b (cost=0.00..1.28 rows=28 width=32)<br> -> Index Scan using landcover6in_2017_st_convexhull_idx on landcover6in_2017 a (cost=0.41..1844.10 rows=95 width=771)<br> Index Cond: ((rast)::geometry && b.geom_2263)<br> Filter: _st_intersects(b.geom_2263, rast, NULL::integer)</div><div><br></div><div><br></div><div><br></div><div>--Polygonized Raster/Vector Overlay<br></div><div>explain select lc_2017_value,<br>sum(st_area(st_intersection(a.geom_2263, b.geom_2263))) as area_ft2<br>from base_rasters.landcover6in_2017_polygons a<br>join scratch.smallsample b<br>on st_intersects(a.geom_2263, b.geom_2263)<br>group by lc_2017_value;</div><div><br></div><div>HashAggregate (cost=12518962.15..12518962.23 rows=8 width=16)<br> Group Key: a.lc_2017_value<br> -> Nested Loop (cost=0.42..1295125.12 rows=446631 width=1388)<br> -> Seq Scan on smallsample b (cost=0.00..1.28 rows=28 width=32)<br> -> Index Scan using landcover6in_2017_polygons_geom_idx on landcover6in_2017_polygons a (cost=0.42..46238.47 rows=1595 width=1356)<br> Index Cond: (geom_2263 && b.geom_2263)<br> Filter: st_intersects(geom_2263, b.geom_2263)</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Jan 31, 2022 at 2:42 AM Florian Nadler <<a href="mailto:florian.nadler@cybertec.at" target="_blank">florian.nadler@cybertec.at</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<p>Hi,</p>
<p>can you provide execution plans for both queries?</p>
<p>In the meantime, please try the following variants:</p>
<pre style="background-color:rgb(255,255,255);color:rgb(8,8,8);font-family:"JetBrains Mono",monospace"><span style="color:rgb(0,51,179)">select
</span>(<span style="color:rgb(0,0,0)">foo</span>.<span style="color:rgb(0,0,0)">geomval</span>).val,
<span style="font-style:italic">sum</span>(<span style="color:rgb(0,98,122);font-style:italic">st_area</span>((<span style="color:rgb(0,0,0)">geomval</span>).geom)) <span style="color:rgb(0,51,179)">as </span><span style="color:rgb(0,0,0)">area_ft2
</span><span style="color:rgb(0,51,179)">from </span>(
<span style="color:rgb(0,51,179)">select </span>(<span style="color:rgb(0,98,122);font-style:italic">st_intersection</span>(<span style="color:rgb(0,0,0)">a</span>.<span style="font-style:italic">rast</span>, <span style="color:rgb(0,0,0)">b</span>.<span style="font-style:italic">geom_2263</span>)) <span style="color:rgb(0,51,179)">as </span><span style="color:rgb(0,0,0)">geomval
</span><span style="color:rgb(0,0,0)"> </span><span style="color:rgb(0,51,179)">from </span>base_rasters.landcover6in_2017 <span style="color:rgb(0,0,0)">a
</span><span style="color:rgb(0,0,0)"> </span><span style="color:rgb(0,51,179)">join </span>scratch.smallsample <span style="color:rgb(0,0,0)">b
</span><span style="color:rgb(0,0,0)"> </span><span style="color:rgb(0,51,179)">on </span><span style="color:rgb(0,98,122);font-style:italic">st_intersects</span>(<span style="color:rgb(0,0,0)">a</span>.<span style="font-style:italic">rast</span>::<span style="color:rgb(0,51,179)">geometry</span>, <span style="color:rgb(0,0,0)">b</span>.<span style="font-style:italic">geom_2263</span>)) <span style="color:rgb(0,51,179)">as </span><span style="color:rgb(0,0,0)">foo
</span><span style="color:rgb(0,51,179)">group by </span>val;</pre>
<pre style="background-color:rgb(255,255,255);color:rgb(8,8,8);font-family:"JetBrains Mono",monospace"><span style="color:rgb(0,51,179)">select
</span>(<span style="color:rgb(0,0,0)">foo</span>.<span style="color:rgb(0,0,0)">geomval</span>).val,
<span style="font-style:italic">sum</span>(<span style="color:rgb(0,98,122);font-style:italic">st_area</span>((<span style="color:rgb(0,0,0)">geomval</span>).geom)) <span style="color:rgb(0,51,179)">as </span><span style="color:rgb(0,0,0)">area_ft2
</span><span style="color:rgb(0,51,179)">from </span>(
<span style="color:rgb(0,51,179)">select </span>(<span style="color:rgb(0,98,122);font-style:italic">st_intersection</span>(<span style="color:rgb(0,0,0)">a</span>.<span style="font-style:italic">rast</span>, <span style="color:rgb(0,0,0)">b</span>.<span style="font-style:italic">geom_2263</span>)) <span style="color:rgb(0,51,179)">as </span><span style="color:rgb(0,0,0)">geomval
</span><span style="color:rgb(0,0,0)"> </span><span style="color:rgb(0,51,179)">from </span>base_rasters.landcover6in_2017 <span style="color:rgb(0,0,0)">a
</span><span style="color:rgb(0,0,0)"> </span><span style="color:rgb(0,51,179)">join </span>scratch.smallsample <span style="color:rgb(0,0,0)">b
</span><span style="color:rgb(0,0,0)"> </span><span style="color:rgb(0,51,179)">on </span><span style="color:rgb(0,98,122);font-style:italic">st_intersects</span>(<span style="color:rgb(0,0,0)">a</span>.<span style="font-style:italic">rast</span>, <span style="color:rgb(0,0,0)">b</span>.<span style="font-style:italic">geom_2263</span>) <span style="color:rgb(0,51,179)">where </span><span style="color:rgb(0,0,0)">a</span>.<span style="font-style:italic">rast </span><span style="color:rgb(0,0,0)">&& b</span>.<span style="font-style:italic">geom_2263</span>) <span style="color:rgb(0,51,179)">as </span><span style="color:rgb(0,0,0)">foo
</span><span style="color:rgb(0,51,179)">group by </span>val</pre>
<div>Am 31.01.2022 um 04:32 schrieb Mike
Treglia:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>Hi all,</div>
<div><br>
</div>
<div>I was exploring raster/vector overlays, basically to
calculate the area of each of several landcover classes (from
raster data) within an area or sets of areas (delineated in
polygon/multipolygon data). In the past, I had ended up
polygonizing the raster, making sure the polygonized layer had
a spatial index, and developing a query from there. <br>
</div>
<div><br>
</div>
<div>But I wanted to come back to the problem and see if I could
do it in what seemed like the more elegant way, using the
raster directly without an intermediate step of polygonizing
it. While I'm able to do it, at least on a small sample area,
it's at a huge performance cost. <br>
</div>
<div><br>
</div>
<div>I'm wondering if I'm just missing something I need to do to
make the raster-based version operate more efficiently. (For
what it's worth, rasters like this, are also slow to load into
QGIS and such [though once loaded, are fairly quick to
render], so I wonder if that's related at all and fixable.)<br>
</div>
<div><br>
</div>
<div>My test case is in New York City - I'm working with a
six-inch resolution landcover dataset for the entirety of NYC
(<a href="https://data.cityofnewyork.us/Environment/Land-Cover-Raster-Data-2017-6in-Resolution/he6d-2qns" target="_blank">https://data.cityofnewyork.us/Environment/Land-Cover-Raster-Data-2017-6in-Resolution/he6d-2qns</a>),
which I'm overlaying with a small subset of parcels in a small
geographic area. In this example, below, I'm just adding up
the area for each landcover class across the focal parcels for
simplicity. When using the polygonized landcover data, it
takes about 170ms. When using the raster landcover data, it
takes about 1 min 20 seconds. <br>
</div>
<div><br>
</div>
<div>Below are the queries, as well as the information about the
raster table in PostGIS, and the raster2pgsql code I used to
load the layer into the database. Curious to hear any thoughts
from folks on the list. Of course if there's anything else I
can share that would be helpful, let me know<br>
</div>
<div><br>
</div>
<div>Thanks so much! Best,</div>
<div>Mike<br>
</div>
<div><br>
</div>
<div>Here are the queries I'm running:</div>
<div>1) Original Raster over Polygons- ~1 min 20 sec<br>
</div>
<div>---------<br>
</div>
<div>select <br>
(foo.geomval).val, <br>
sum(st_area((geomval).geom)) as area_ft2 <br>
from (<br>
select (st_intersection(a.rast, b.geom_2263)) as geomval<br>
from base_rasters.landcover6in_2017 a <br>
join scratch.smallsample b<br>
on st_intersects(a.rast, b.geom_2263)) as foo<br>
group by val;<br>
<br>
2) Polygonized Raster over Polygons ~0.170 ms<br>
</div>
<div>---------<br>
</div>
<div>select lc_2017_value, <br>
sum(st_area(st_intersection(a.geom_2263, b.geom_2263))) as
area_ft2<br>
from base_rasters.landcover6in_2017_polygons a<br>
join scratch.smallsample b<br>
on st_intersects(a.geom_2263, b.geom_2263)<br>
group by lc_2017_value;</div>
<div><br>
</div>
<div><br>
</div>
<div>Here's the information for the raster table. (I had added a
second index in hopes it might help but no, it didn't).</div>
<div>---------</div>
<div> Table
"base_rasters.landcover6in_2017"<br>
Column | Type | Collation | Nullable |
Default<br>
--------+---------+-----------+----------+-------------------------------------------------------------<br>
rid | integer | | not null |
nextval('base_rasters.landcover6in_2017_rid_seq'::regclass)<br>
rast | raster | | |<br>
Indexes:<br>
"landcover6in_2017_pkey" PRIMARY KEY, btree (rid)<br>
"landcover6in_2017_envidx" gist (st_envelope(rast))<br>
"landcover6in_2017_st_convexhull_idx" gist
(st_convexhull(rast))<br>
Check constraints:<br>
"enforce_height_rast" CHECK (st_height(rast) = ANY
(ARRAY[128, 46]))<br>
"enforce_max_extent_rast" CHECK (st_envelope(rast) @
'0103000020D70800000100000005000000C3F528DC3DD72B41CCCCCCCCB46BFC40C3F528DC3DD72B413333333349B31041E27A14EE9E4930413333333349B31041E2<br>
7A14EE9E493041CCCCCCCCB46BFC40C3F528DC3DD72B41CCCCCCCCB46BFC40'::geometry)
NOT VALID<br>
"enforce_nodata_values_rast" CHECK
(_raster_constraint_nodata_values(rast) =
'{0.0000000000}'::numeric[])<br>
"enforce_num_bands_rast" CHECK (st_numbands(rast) = 1)<br>
"enforce_out_db_rast" CHECK
(_raster_constraint_out_db(rast) = '{f}'::boolean[])<br>
"enforce_pixel_types_rast" CHECK
(_raster_constraint_pixel_types(rast) = '{8BUI}'::text[])<br>
"enforce_same_alignment_rast" CHECK
(st_samealignment(rast,
'0100000000000000000000E03F000000000000E0BFC3F528DCBDB92E413333333349B3104100000000000000000000000000000000D708000001000100'::<br>
raster))<br>
"enforce_scalex_rast" CHECK
(round(st_scalex(rast)::numeric, 10) = round(0.5, 10))<br>
"enforce_scaley_rast" CHECK
(round(st_scaley(rast)::numeric, 10) = round(- 0.5, 10))<br>
"enforce_srid_rast" CHECK (st_srid(rast) = 2263)<br>
"enforce_width_rast" CHECK (st_width(rast) = 128)</div>
<div><br>
</div>
<div>Here's the raster2pgsql code I used to load the raster in
the first place:</div>
<div>-------<br>
</div>
<div>raster2pgsql -s 2263 -d -C -t 128x128 -M -I -l 4,16
"NYC_2017_LiDAR_LandCover.tif" base_rasters.landcover6in_2017
| psql -h localhost -U postgres -d nycdb -v ON_ERROR_STOP=1</div>
<div><br>
</div>
<div>Lastly - here's my PostGIS info (Running on Windows 10, 64
bit): <br>
</div>
<div>POSTGIS="3.1.1 3.1.1" [EXTENSION] PGSQL="130"
GEOS="3.9.0-CAPI-1.14.1" SFCGAL="1.3.8" PROJ="7.1.1"
GDAL="GDAL 3.2.1, released 2020/12/29" LIBXML="2.9.9"
LIBJSON="0.12" LIBPROTOBUF="1.2.1" WAGYU="0.5.0 (Internal)"
TOPOLOGY RASTER</div>
<div><br>
</div>
</div>
<br>
<fieldset></fieldset>
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