[GIS] Get the intersection of a polygon with a generated buffer in postgis

postgis

I have two tables. One has points in EPSG:4326 and the other one has polygons also in EPSG:4326.
I loaded these two as layers in geoserver and show them using openlayers (as shown in image)

Now I want to write a query in postgis in which I find the intersection area of each green point (buffered by 200 meters) with the polygons.

I have written this query:

SELECT c.name, d.name FROM points c, polygons d WHERE ST_INTERSECTS(d.geom, ST_BUFFER(c.geom,500))

But I get no results. If I increase the buffer size to 5000000 then I get results.

  1. So the question is if there is a better way to do this without using a Buffer.
  2. If there is projection issue in which I am missing.

EDIT

I followed the advice of @HimBromBeere and transformed my geometries to EPSG: 2100 (which is in metres).
The problem still remains as executing this query I get as a result 0, which doesnt make any sense.

SELECT ST_AREA(
      ST_INTERSECTION(ST_Buffer
      (ST_Transform(ST_SetSRID(c.geom, 4326),2100),200),
      ST_Transform(ST_SetSRID(d.geom, 4326),2100))) 
      FROM categoriesdata c, dimoi d

enter image description here

Best Answer

ST_Buffer will consider your spatial reference. So as you have geographic coordinates you have to provide your buffer-size in degrees as well.

Alternativly you may transform your geometries into a metric spatial-refrence first as proposed here:

SELECT ST_Buffer(
    ST_Transform(
        ST_SetSRID(ST_MakePoint(-71.063526, 42.35785), 4326),
        myNewReferenceSystem), 
    200); // buffer by 200m
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