Function sbas_selection 

pub fn sbas_selection(lat: f64, lon: f64) -> Option<Constellation>

Select an augmentation system conveniently, based on given location in decimal degrees

extern crate gnss_rs as gnss;
use gnss::prelude::*;
use gnss::sbas_selection;

let paris = (48.808378, 2.382682); // lat, lon [ddeg]
let sbas = sbas_selection(paris.0, paris.1);
assert_eq!(sbas, Some(Constellation::EGNOS));

let antartica = (-77.490631,  91.435181); // lat, lon [ddeg]
let sbas = sbas_selection(antartica.0, antartica.1);
assert_eq!(sbas.is_none(), true);