Truncate precision in CLLocationCoordinate2D to relevant decimal places

[JThramer]

When crafting a custom RouteOptions request , the user has the ability to use the full Double bitwidth to describe CLLocationCoordinate2D waypoints. This causes us to potentially emit really long requests when we end up requesting a route.

We only pay attention to the the fifth or sixth decimal place in the API (depending on the API version I think? cc @1ec5), so we should truncate our values to match at request time.

/cc @mapbox/navigation-ios

[1ec5]

We only pay attention to the the fifth or sixth decimal place in the API (depending on the API version I think?)

OSRM uses up to six digits of precision. That has been the case since at least OSRM v0.3.8, which came before Directions API v4, the first version of the API that this library supported.

[1ec5]

This is where we’d round then truncate:

https://github.com/mapbox/MapboxDirections.swift/blob/6bf93daa11ed21b2b31352f199ac1316fb1c287b/MapboxDirections/MBDirectionsOptions.swift#L331

[1ec5]

For reference, MapboxGeocoder.swift uses a format string to truncate (not round) to five digits of precision:

https://github.com/mapbox/MapboxGeocoder.swift/blob/c5fcfe127b0b2c07b7bd9d5006f7f4fe0dc04b27/MapboxGeocoder/MBGeocodeOptions.swift#L185