CQL support

OGC Common Query Language (CQL2) is a generic language designed to provide enhanced query and subset/filtering to (primarily) feature and record data.

Providers

CQL2 support is implemented in various pygeoapi feature and record providers. See the feature and metadata provider sections for current provider support.

Limitations

Support of CQL is limited to Basic CQL2 and thus it allows to query with the following predicates:

comparison predicates
spatial predicates
temporal predicates

Formats

Supported providers leverage the CQL2 dialect with the JSON encoding CQL-JSON.

PostgreSQL supports both CQL2 JSON and CQL text dialects.

Queries

The PostgreSQL provider uses pygeofilter allowing a range of filter expressions, see examples for:

Using Elasticsearch the following type of queries are supported currently:

between predicate query
Logical and query with between and eq expression
Spatial query with bbox

Note that when using a spatial operator in your filter expression, geometries are by default interpreted as being in the OGC:CRS84 Coordinate Reference System. If you wish to provide geometries in other CRS, use the filter-crs query parameter with a suitable value.

Alternatively, a geometry’s CRS may also be included using Extended Well-Known Text, in which case it will override the value of filter-crs (if any) - this can be useful if your filtering expression is complex enough to need multiple geometries expressed in different CRSs. The standard way of providing filter-crs as an additional query parameter is preferable for most cases.

Examples

A BETWEEN example for a specific property through an HTTP POST request:

curl --location --request POST 'http://localhost:5000/collections/nhsl_hazard_threat_all_indicators_s_bc/items?f=json&limit=50&filter-lang=cql-json' \
--header 'Content-Type: application/query-cql-json' \
--data-raw '{
  "op": "between",
  "args": [
      {"property": "properties.MHn_Intensity"},
      [0.59, 0.60]
  ]
}'

Or

curl --location --request POST 'http://localhost:5000/collections/recentearthquakes/items?f=json&limit=10&filter-lang=cql-json'
--header 'Content-Type: application/query-cql-json'
--data-raw '{
  "op": "between",
  "args": [
      {"property": "ml"},
      [4, 4.5]
  ]
}'

The same BETWEEN query using HTTP GET request formatted as CQL text and URL encoded as below:

curl "http://localhost:5000/collections/recentearthquakes/items?f=json&limit=10&filter=ml%20BETWEEN%204%20AND%204.5"

An EQUALS example for a specific property:

curl --location --request POST 'http://localhost:5000/collections/recentearthquakes/items?f=json&limit=10&filter-lang=cql-json'
--header 'Content-Type: application/query-cql-json'
--data-raw '{
  "op": "=",
  "args": [
    {"property": "user_entered"},
    "APBE"
  ]
}'

A CROSSES example via an HTTP GET request. The CQL text is passed via the filter parameter.

curl "http://localhost:5000/collections/hot_osm_waterways/items?f=json&filter=CROSSES(foo_geom,%20LINESTRING(28%20-2,%2030%20-4))"

A DWITHIN example via HTTP GET and using a custom CRS for the filter geometry:

curl "http://localhost:5000/collections/beni/items?filter=DWITHIN(geometry,POINT(1392921%205145517),100,meters)&filter-crs=http://www.opengis.net/def/crs/EPSG/0/3857"

The same example, but this time providing a geometry in EWKT format:

curl "http://localhost:5000/collections/beni/items?filter=DWITHIN(geometry,SRID=3857;POINT(1392921%205145517),100,meters)"

Note that the CQL text has been URL encoded. This is required in curl commands but when entering in a browser, plain text can be used e.g. CROSSES(foo_geom, LINESTRING(28 -2, 30 -4)).