The code of detail is in http://kob.blog.jp/archives/2016-09-19.html

nmea-to-sonygps-converter.go

package main

import (
  "bufio"
  "fmt"
  "os"
)

func main() {
  SONYHEAD := "@Sonygps/ver1.0/wgs-84"
  DUMMYVTG := "$GPVTG,0.000,T,,M,0.000,N,0.000,K*60"

  var fp *os.File
  var err error

  if len(os.Args) < 2 {
    fp  = os.Stdin
  } else {
    fp, err = os.Open(os.Args[1])
    if err != nil {
      panic(err)
    }
    defer fp.Close()
  }

  filename := "./" + os.Args[1] + ".log"
  wf, err := os.Create(filename)
  if err != nil {
    panic(err)
  }
  defer wf.Close()

  wf.Write(([]byte)(SONYHEAD + "\r\n"))

  scanner := bufio.NewScanner(fp)
  count := 0
  for scanner.Scan() {
    fmt.Println(scanner.Text())
    wf.Write(([]byte)(scanner.Text() + "\r\n"))
    if(count%2 == 1){
      wf.Write(([]byte)(DUMMYVTG + "\r\n"))
    }
    count = count + 1
  }
  if err := scanner.Err(); err != nil {
    panic(err)
  }
}