Haversine distance macro doesn't support kms

[joellabes]

Describe the bug

The macro to calculate the haversine distance between two points always returns its result in miles, which isn't useful for people who use the metric system

Steps to reproduce

• Work somewhere other than Liberia, Myanmar, the United Kingdom and the United States
• Use the haversine_distance macro

Expected results

• The option to get results in either miles or kilometres (or even kilometers)

Actual results

• Results in miles

System information

The contents of your packages.yml file:

packages:
  - package: fishtown-analytics/dbt_utils
    version: 0.6.3
  
  - package: fishtown-analytics/audit_helper
    version: 0.3.0

  - package: fishtown-analytics/codegen
    version: 0.3.1

  - package: fishtown-analytics/redshift
    version: 0.4.1

Which database are you using dbt with?

• postgres
• redshift
• bigquery
• snowflake
• other (specify: ____________)

The output of dbt --version:

0.19.0 (dbt Cloud)

Additional context

The great circle calculator linked from the original macro's source says to use 6373km as the radius of the Earth, which is as good a number as any

Are you interested in contributing the fix?

Yes, but not for a while.

[bastienboutonnet]

We've taken an approach on this to just wrap that macro in another macro that divides the results of the original haversine macro by 1.60934

May not be super exact but since we're already in the realm of non exact things that might work out.

I'd be happy to PR the haversine data macro and maybe make it take a param for km or mi

[joellabes]

Resolved by #340!