PostGIS and Korma

postgis.clj

(ns postgis 
  (:require [clj-json.core :as json])
  (:use korma.core korma.db korma.sql.engine))

(defn intersects [first-geom second-geom]
  "An extended Korma predicate that uses the PostGIS function ST_Intersects." 
  (sql-func "ST_Intersects" first-geom second-geom))

(defn from-wkt [wkt]
  "Create a PostGIS geometry with geographic SRID from WKT using ST_GeomFromText."
  (sql-func "ST_GeomFromText" wkt (int 4326)))

(defn from-geojson [geojson]
  "Create a PostGIS geometry from GeoJSON using ST_GeomFromGeoJSON."
  (sql-func "ST_GeomFromGeoJSON" geojson))

(defn as-geojson [pg-geom]
  "Create a GeoJSON geometry from a PostGIS field, adding a CRS definition in 
   'short' format and restricting decimal digits to 3."
  (sql-func "ST_AsGeoJSON" pg-geom (int 3) (int 2)))

(defn row->geojson-feature [geometry-field row]
  "Convert a row containing a key which maps to a GeoJSON string
   to an updated row containing structured data by parsing the GeoJSON."
  (let [geojson (geometry-field row)
        properties (dissoc row geometry-field)]
     {:type "Feature",
      :properties properties,
      :geometry (if (= nil geojson)
                  nil
                  (json/parse-string geojson))}))

(defentity locations
           (pk :short_name)
           (table :locations)
           (database scratch))

(defn- jsonize [rows]
  (map #(row->geojson-feature :loc_geometry %1) rows))

(defn get-locations* []
  (-> (select* locations)
      (fields :name
              :short_name
              [(as-geojson :loc_geometry) :loc_geometry])))

(defn- get-intersecting-locations* [wkt]
  (-> (get-locations*)
      (where (intersects :loc_geometry wkt))))

(defn get-intersecting-locations [wkt]
  "Find locations intersecting with the specified geometry."
  (jsonize (select (get-intersecting-locations* wkt))))