Aggregating geometry features on geometry simplification using PostGIS?

Question

PostGIS has ST_Simplify functionality which gets one multiline as input and returns one output multiline where the general shape of lines are retained while eliminating unnecessary detail.

Instead of one multiline, I have a table with a LineString geometry column (street segment) and an integer column (traffic velocity of that street). I can create a single multiline out of that LineString column and simplify it, but I need to know traffic velocity of simplified geometries too. Is there any tool to aggregate data of integer column into simplified lines?

Answer 1

If I understood your question right you should get started with a simple sql query

select velocity, st_simplify(geom, 0.1) as geom from lines;

Are you sure you want to aggregate lines to one single giant multiline?
If you really need that then you could GROUP BY your velocity column.

select
  velocity,
  st_simplify(st_collect(geom), 0.1)
from lines
group by velocity;