difference between st_accum and st_collect

Question

Can anyone please tell me the difference between ST_Accum and ST_Collect of PostGIS. https://postgis.net/docs/ST_Accum.html

https://postgis.net/docs/ST_Collect.html

Answer 1

The ST_Accum function creates an array of input geometries, while ST_Collect creates a Geometry collection.

Think of it this way. If your inputs are a Bunch of Points, ST_Accum will return an array of points, while ST_Collect will return a Multi-Point.

If the inputs were lines, the ST_Collect would return a Multi-Line and so on.

Answer 2

The role of ST_accum and ST_Collect are different :

• The ST_Accum functions creates an array of input geometries (doc),
• while ST_Collect function create a geometry from an input array (doc).

So, you can use the output of ST_Accum as the input of ST_Collect.

The inverse will create an array with one element.