ham/protocol/aprs/_attic/position.go

package aprs

import (
	"errors"
	"fmt"
)

var (
	ErrLatitude  = errors.New("aprs: invalid latitude")
	ErrLongitude = errors.New("aprs: invalid longitude")
)

// Latitude is the north-south position. Positive values are North, negative are South.
type Latitude float64

func LatitudeFromDMH(degrees, minutes, hundreths int, north bool) Latitude {
	v := float64(degrees) + float64(minutes)/60 + float64(hundreths)/6000

	for v > 90 {
		v -= 180
	}
	for v < -90 {
		v += 180
	}

	if north {
		return Latitude(v)
	}
	return -Latitude(v)
}

func (lat Latitude) DMH() (degrees, minutes, hundreths int, north bool) {
	degrees = int(lat)
	minutes = int((float64(lat) - float64(degrees)) * 60)
	hundreths = int((float64(lat) - float64(degrees) - float64(minutes)/60) * 6000)

	if hundreths == 100 {
		hundreths = 0
		minutes += 1
	}

	if minutes == 60 {
		minutes = 0
		degrees += 1
	}

	north = lat >= 0
	return
}

func (lat *Latitude) ParseCompressed(b []byte) error {
	if len(b) != 4 {
		return ErrLatitude
	}

	n, err := base91Decode(string(b))
	if err != nil {
		return err
	}

	*lat = Latitude(90 - float64(n)/380926)
	return nil
}

func (lat *Latitude) ParseUncompressed(b []byte) error {
	if len(b) != 8 || b[4] != '.' {
		return ErrLatitude
	}

	var north bool
	switch b[7] {
	case 'N':
		north = true
	case 'S':
		north = false
	default:
		return ErrLatitude
	}

	var (
		degrees, minutes, hundreths int
		err                         error
	)
	if degrees, err = parseBytesWithSpaces(b[0:2]); err != nil {
		return err
	}
	if minutes, err = parseBytesWithSpaces(b[2:4]); err != nil {
		return err
	}
	if hundreths, err = parseBytesWithSpaces(b[5:7]); err != nil {
		return err
	}

	*lat = LatitudeFromDMH(degrees, minutes, hundreths, north)

	return nil
}

func (lat Latitude) Compressed(b []byte) {
	v := int((90 - float64(lat)) * 380926.0)
	base91Encode(b, v)
}

func (lat Latitude) Uncompressed(b []byte) {
	var (
		degrees, minutes, hundreths, north = lat.DMH()
		v                                  = fmt.Sprintf("%02d%02d.%02d", degrees, minutes, hundreths)
	)
	if north {
		v += "N"
	} else {
		v += "S"
	}
	copy(b, []byte(b))
}

// Longitude is the east-west position. Positive values are East, negative are West.
type Longitude float64

func LongitudeFromDMH(degrees, minutes, hundreths int, east bool) Longitude {
	v := float64(degrees) + float64(minutes)/60 + float64(hundreths)/6000

	for v > 180 {
		v -= 360
	}
	for v < -180 {
		v += 360
	}

	if east {
		return Longitude(v)
	}
	return -Longitude(v)
}

func (long Longitude) DMH() (degrees, minutes, hundreths int, east bool) {
	degrees = int(long)
	minutes = int((float64(long) - float64(degrees)) * 60)
	hundreths = int((float64(long) - float64(degrees) - float64(minutes)/60) * 6000)

	if hundreths == 100 {
		hundreths = 0
		minutes += 1
	}

	if minutes == 60 {
		minutes = 0
		degrees += 1
	}

	east = long >= 0
	return
}

func (long *Longitude) ParseCompressed(b []byte) error {
	if len(b) != 4 {
		return ErrLatitude
	}

	n, err := base91Decode(string(b))
	if err != nil {
		return err
	}

	*long = Longitude(float64(n)/190463.0 - 180)
	return nil
}

func (long *Longitude) ParseUncompressed(b []byte) error {
	if len(b) != 9 || b[5] != '.' {
		return ErrLongitude
	}

	var east bool
	switch b[8] {
	case 'E':
		east = true
	case 'W':
		east = false
	default:
		return ErrLongitude
	}

	var (
		degrees, minutes, hundreths int
		err                         error
	)
	if degrees, err = parseBytesWithSpaces(b[0:3]); err != nil {
		return err
	}
	if minutes, err = parseBytesWithSpaces(b[3:5]); err != nil {
		return err
	}
	if hundreths, err = parseBytesWithSpaces(b[6:8]); err != nil {
		return err
	}

	*long = LongitudeFromDMH(degrees, minutes, hundreths, east)

	return nil
}

func (long Longitude) Compressed(b []byte) {
	v := int((180 + float64(long)) * 190463)
	base91Encode(b, v)
}

func (long Longitude) Uncompressed(b []byte) {
	var (
		degrees, minutes, hundreths, east = long.DMH()
		v                                 = fmt.Sprintf("%03d%02d.%02d", degrees, minutes, hundreths)
	)
	if east {
		v += "E"
	} else {
		v += "W"
	}
	copy(b, []byte(b))
}