wrap latitude and longitude values around the poles in order to normalize their ranges

wrap.rs

/// Normalize co-ordinates that lie outside of the normal ranges.
/// Longitude wrapping simply requires adding +- 360 to the value until it comes into range.
///
/// For the latitude values, we need to flip the longitude whenever the latitude crosses a pole.
///
/// Description and original source was ported from https://gist.github.com/missinglink/d0a085188a8eab2ca66db385bb7c023a to rust
pub fn wrap_latlon(mut lat: f64, mut lon: f64) -> (f64, f64) {
    let quadrant = ((lat.abs() / 90_f64).floor() % 4_f64) as i8;
    let pole = if lat > 0_f64 { 90_f64 } else { -90_f64 };
    let offset = lat % 90_f64;

    match quadrant {
        0 => {
            lat = offset;
        }
        1 => {
            lat = pole - offset;
            lon += 180_f64
        }
        2 => {
            lat = -offset;
            lon += 180_f64;
        }
        3 => {
            lat = -pole + offset;
        }
        _ => {}
    }

    if lon > 180_f64 || lon < -180_f64 {
        lon -= ((lon + 180_f64) / 360_f64).floor() * 360_f64;
    }

    (lat, lon)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_control() {
        // Control - no wrapping required
        assert_eq!(
            wrap_latlon(55.555_f64, 22.222_f64),
            (55.555_f64, 22.222_f64)
        );
    }

    #[test]
    fn test_latitude_positive() {
        // Positive latitude wrapping - 1 degree
        assert_eq!(wrap_latlon(1_f64, 0_f64), (1_f64, 0_f64));

        // Positive latitude wrapping - 91 degrees
        assert_eq!(wrap_latlon(91_f64, 0_f64), (89_f64, 180_f64));

        // Positive latitude wrapping - 181 degrees
        assert_eq!(wrap_latlon(181_f64, 0_f64), (-1_f64, 180_f64));

        // Positive latitude wrapping - 271 degrees
        assert_eq!(wrap_latlon(271_f64, 0_f64), (-89_f64, 0_f64));

        // Positive latitude wrapping - 361 degrees
        assert_eq!(wrap_latlon(361_f64, 0_f64), (1_f64, 0_f64));

        // Positive latitude wrapping - 631 degrees
        assert_eq!(wrap_latlon(631_f64, 0_f64), (-89_f64, 0_f64));

        // Positive latitude wrapping - 721 degrees
        assert_eq!(wrap_latlon(721_f64, 0_f64), (1_f64, 0_f64));
    }

    #[test]
    fn test_latitude_negative() {
        // Negative latitude wrapping - 1 degree
        assert_eq!(wrap_latlon(-1_f64, 0_f64), (-1_f64, 0_f64));

        // Negative latitude wrapping - 91 degrees
        assert_eq!(wrap_latlon(-91_f64, 0_f64), (-89_f64, 180_f64));

        // Negative latitude wrapping - 181 degrees
        assert_eq!(wrap_latlon(-181_f64, 0_f64), (1_f64, 180_f64));

        // Negative latitude wrapping - 271 degrees
        assert_eq!(wrap_latlon(-271_f64, 0_f64), (89_f64, 0_f64));

        // Negative latitude wrapping - 361 degrees
        assert_eq!(wrap_latlon(-361_f64, 0_f64), (-1_f64, 0_f64));

        // Negative latitude wrapping - 631 degrees
        assert_eq!(wrap_latlon(-631_f64, 0_f64), (89_f64, 0_f64));

        // Positive latitude wrapping - 721 degrees
        assert_eq!(wrap_latlon(721_f64, 0_f64), (1_f64, 0_f64));
    }

    #[test]
    fn test_longitude_positive() {
        // Positive longitude wrapping - 1 degree
        assert_eq!(wrap_latlon(0_f64, 1_f64), (0_f64, 1_f64));

        // Positive longitude wrapping - 181 degrees
        assert_eq!(wrap_latlon(0_f64, 181_f64), (0_f64, -179_f64));

        // Positive longitude wrapping - 271 degrees
        assert_eq!(wrap_latlon(0_f64, 271_f64), (0_f64, -89_f64));

        // Positive longitude wrapping - 361 degrees
        assert_eq!(wrap_latlon(0_f64, 361_f64), (0_f64, 1_f64));

        // Positive longitude wrapping - 631 degrees
        assert_eq!(wrap_latlon(0_f64, 631_f64), (0_f64, -89_f64));

        // Positive longitude wrapping - 721 degrees
        assert_eq!(wrap_latlon(0_f64, 721_f64), (0_f64, 1_f64));
    }

    #[test]
    fn test_longitude_negative() {
        // Negative longitude wrapping - 1 degree
        assert_eq!(wrap_latlon(0_f64, -1_f64), (0_f64, -1_f64));

        // Negative longitude wrapping - 181 degrees
        assert_eq!(wrap_latlon(0_f64, -181_f64), (0_f64, 179_f64));

        // Negative longitude wrapping - 271 degrees
        assert_eq!(wrap_latlon(0_f64, -271_f64), (0_f64, 89_f64));

        // Negative longitude wrapping - 361 degrees
        assert_eq!(wrap_latlon(0_f64, -361_f64), (0_f64, -1_f64));

        // Negative longitude wrapping - 631 degrees
        assert_eq!(wrap_latlon(0_f64, -631_f64), (0_f64, 89_f64));

        // Negative longitude wrapping - 721 degrees
        assert_eq!(wrap_latlon(0_f64, -721_f64), (0_f64, -1_f64));
    }
}