How to calculate the length of each way in a set in Overpass - use of foreach and sum(length())

Question

I need help understanding the correct use of foreach and sum(length()) in an Overpass query. I've written a query for extracting all relations and ways of a given type within a bounding box, and then, if it finds any, filtering out the ones that don't have ways with highway=footway tags within them (it also extracts parks, but maybe not relevant to the question, apart from explaining why I've named all the sets).

way(8.97266,-79.58028,9.01195,-79.53501)[leisure=park][natural!=wood]->.parks;
(
  rel(8.97266,-79.58028,9.01195,-79.53501)[natural=wood];
  way(8.97266,-79.58028,9.01195,-79.53501)[natural=wood];
)->.tempOther;
if (tempOther.count(ways) != 0)
{
  .tempOther map_to_area->.aOther;
  way(area.aOther)[highway=footway]->.fOther;
  foreach {
    (.fOther; .fOther >;);
    is_in;
    (
      rel(pivot)[natural=wood]->.rOther;
      way(pivot)[natural=wood]->.wOther;
    )->.other;
  }
}
(
  .parks;
  .other;
 );
out geom;

I would further like to exclude relations and ways that only contain short footways, for example, less than 1000 m. I've tried using if (sum(length()) > 1000) {...} (and tried fOther.sum(length())) within the foreach loop, but these fail to do what I think they should do... calculate the length of each individual way (as far as I can tell, it's calculating the total length of all the ways in the set).

Having read the Overpass Language reference and guide, I'm probably still misunderstanding how foreach and/or sum(length()) work.

How do I use them correctly in this situation?

Answer 1

I think I found the solution thanks to the answer to another question here: https://help.openstreetmap.org/questions/62730/overpass-query-to-find-multipolygon-relations-with-just-one-member

In my case, I added an if filter and length() evaluator to the line of code above my foreach loop. So way(area.aOther)[highway=footway]->.fOther; becomes

way(area.aOther)[highway=footway](if: length() > 1000 )->.fOther;

and I get what I needed (i.e. relations and ways containing footways longer than x meters).