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<span style="font-family: Calibri, Helvetica, sans-serif;">Hello, </span></div>
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<span style="font-family: Calibri, Helvetica, sans-serif;">I am trying to simplify a polygon by reducing the precision using ST_Union with the gridSize parameter ( I am using postgis 3.1 and GEOS 3.9.1). I have read that it is possible to do that by a union
of a geometry with an empty geometry (http://blog.cleverelephant.ca/2020/12/waiting-postgis-31-3.html). However, does not works for me ( maybe is my fault because I am new with postgis). I have tried as follows:</span></div>
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<div><i>CREATE TABLE public.error_union_empty</i></div>
<div><i>(</i></div>
<div><i> geom geometry(MultiPolygon),</i></div>
<div><i> gid integer NOT NULL DEFAULT nextval('fallo_gid_seq'::regclass),</i></div>
<div><i> CONSTRAINT error_union_empty_pkey PRIMARY KEY (gid)</i></div>
<div><i>);</i></div>
<div><i>INSERT INTO error_union_empty</i></div>
<div><i>(SELECT ST_union(geom,ST_GeomFromText('POLYGON EMPTY'), 0.001152) geom</i></div>
<div><i>FROM f_polygon);</i></div>
<div><br>
</div>
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<div><span style="font-family: calibri, helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgba(0, 0, 0, 0);">But the result is an empty table.</span></div>
<div><span style="font-family: calibri, helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgba(0, 0, 0, 0);">Then I tried to do the same but by doing the union with the polygon himself, and this approach seems to work ok.</span></div>
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</span></div>
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<div><i>CREATE TABLE public.error_union_empty2</i></div>
<div><i>(</i></div>
<div><i> geom geometry(MultiPolygon),</i></div>
<div><i> gid integer NOT NULL DEFAULT nextval('fallo_gid_seq'::regclass),</i></div>
<div><i> CONSTRAINT error_union_empty2_pkey PRIMARY KEY (gid)</i></div>
<div><i>);</i></div>
<div><i>insert into error_union_empty2</i></div>
<div><i>select ST_CollectionExtract(ST_union(f_polygon.geom,f_polygon.geom, 0.001152)) geom
</i></div>
<div><i>from f_polygon;</i></div>
<div><br>
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<div>Why is not working the first approach? Have I missed something in the query?</div>
<div>Any help or comments are welcome. </div>
<div>Does anyone knows if is expected to have a simplify with gridsize in the future?</div>
<div><br>
</div>
<div>Thanks!</div>
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