add unit argument and apply conversion for kms

multiply instead of divide and move logic in core macro

rename things a bit

update readme

README.md

@@ -95,7 +95,7 @@ Usage:
 ---
 ### Date/Time
 #### date_spine ([source](macros/datetime/date_spine.sql))
-This macro returns the sql required to build a date spine. The spine will include the `start_date` (if it is aligned to the `datepart`), but it will not include the `end_date`. 
+This macro returns the sql required to build a date spine. The spine will include the `start_date` (if it is aligned to the `datepart`), but it will not include the `end_date`.
 
 Usage:
 ```
@@ -111,9 +111,11 @@ Usage:
 #### haversine_distance ([source](macros/geo/haversine_distance.sql))
 This macro calculates the [haversine distance](http://daynebatten.com/2015/09/latitude-longitude-distance-sql/) between a pair of x/y coordinates.
 
+Optionally takes a `unit` string parameter ('km' or 'mi') which defaults to miles (imperial system).
+
 Usage:
 ```
-{{ dbt_utils.haversine_distance(lat1=<float>,lon1=<float>,lat2=<float>,lon2=<float>) }}
+{{ dbt_utils.haversine_distance(lat1=<float>,lon1=<float>,lat2=<float>,lon2=<float>, unit='mi'<sting>) }}
 ```
 ---
 ### Schema Tests

macros/geo/haversine_distance.sql

@@ -3,17 +3,23 @@ This calculates the distance between two sets of latitude and longitude.
 The formula is from the following blog post:
 http://daynebatten.com/2015/09/latitude-longitude-distance-sql/
 
-The arguments should be float type. 
+The arguments should be float type.
 #}
 
-{% macro haversine_distance(lat1,lon1,lat2,lon2) -%}
-    {{ return(adapter.dispatch('haversine_distance', packages = dbt_utils._get_utils_namespaces())(lat1,lon1,lat2,lon2)) }}
+{% macro haversine_distance(lat1,lon1,lat2,lon2,unit='mi') -%}
+    {{ return(adapter.dispatch('haversine_distance', packages = dbt_utils._get_utils_namespaces())(lat1,lon1,lat2,lon2,unit)) }}
 {% endmacro %}
 
-{% macro default__haversine_distance(lat1,lon1,lat2,lon2) -%}
+{% macro default__haversine_distance(lat1,lon1,lat2,lon2,unit='km') -%}
+{# vanilla macro is in miles #}
+    {% set conversion = '' %}
+{% if unit == 'km' %}
+{# we multiply miles result to get it in kms #}
+    {% set conversion = '* 1.60934' %}
+{% endif %}
 
     2 * 3961 * asin(sqrt((sin(radians(({{lat2}} - {{lat1}}) / 2))) ^ 2 +
     cos(radians({{lat1}})) * cos(radians({{lat2}})) *
-    (sin(radians(({{lon2}} - {{lon1}}) / 2))) ^ 2))
+    (sin(radians(({{lon2}} - {{lon1}}) / 2))) ^ 2)) {{conversion_rate}}
 
 {%- endmacro %}