Overpass API developpement

[Roland Olbricht <>]

Hello,

Although late, I would like to provide the promised follow-up.

First of all, thank you to all who have given feedback. The evaluator 
_is_num_ is now renamed to _is_number_ to be in line with _number_ and 
_date_ and _is_date_.

A still open point is the syntax for tag evaulation.
I agree that pure brackets might confuse users. And that syntax does not 
exist in any way in JavaScript or similar languages. I'm wondering 
whether an approach with a single letter, like

  t[name]
  v[name]

or so would make to tag evaulator more intuitively. I would like to 
stick with the brackets, because people know that as syntax of 
dictionaries. And the tags of an element constitute a dictionary.

That there is close-call syntax with a different meaning in the XAPI 
legacy is admittedly a pity. But we should not throw out that syntax 
just for the sake of purity, not now and not next year. Giving people a 
migration path to the more versatile present and future syntax is more 
important.

But now the promised further examples:


The filter for date ranges is actually a full fledged less than, and 
variants for less-equal, greater-than and greater-equal exist as well:

Find fast roads:
http://overpass-turbo.eu/s/lcg

Look for roads with non-number values:
http://overpass-turbo.eu/s/lch

Or objects that have only a name tag:
http://overpass-turbo.eu/s/lci

Beside this, one can find all objects with similar (or related) properties:
http://overpass-turbo.eu/s/lcj

Enhanced version, this one also gets nodes with level:
http://overpass-turbo.eu/s/lck

Even more, we could get one level up:
http://overpass-turbo.eu/s/lcl

Beside filter, the make statement allows to create objects as desired.
The simplest case is to output where useful a marker:
http://overpass-turbo.eu/s/lcm

This also contains a generalisation of the count.
You could list all values of a tag that exist in a result in addition to 
counting:
http://overpass-turbo.eu/s/lcn

The full list of aggregators, like _set_ and _count_ used here, can be 
found in the specification (TODO).


This version also brings a possibility to rewrite tags lists of objects.
If you do want objects with lots of tags in the result but only need 
some tags
then you can use an approach like this:
http://overpass-turbo.eu/s/lco

This has already been possible with the special output mode [out:csv].
But now you can feed this into your toolchain regardless whether you 
need XML or JSON as well.

Or just combine names:
http://overpass-turbo.eu/s/lcp

In some cases, you only want to knock out one or two tags:
http://overpass-turbo.eu/s/lcq


Finally, this allows to generate is_in-tags on the fly:

  node({{bbox}})[place=village];
  foreach(
    is_in->.a;
    ( convert node ::=::,is_in=a.set([name]); .result; )->.result;
  );
  .result out;

(note: currently no areas on the dev instance, hence no link)

Although it is not fast, it generalizes to other relationships:
http://overpass-turbo.eu/s/lcr

Cheers,

Roland