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gps.go
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gps.go
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/*
Copyright (c) 2015-2016 Christopher Young
Distributable under the terms of The "BSD New" License
that can be found in the LICENSE file, herein included
as part of this header.
gps.go: GPS functions, GPS init, AHRS status messages, other external sensor monitoring.
*/
package main
import (
"fmt"
"log"
"math"
"strconv"
"strings"
"sync"
"time"
"bufio"
"github.com/tarm/serial"
"os"
"os/exec"
)
const (
SAT_TYPE_UNKNOWN = 0 // default type
SAT_TYPE_GPS = 1 // GPxxx; NMEA IDs 1-32
SAT_TYPE_GLONASS = 2 // GLxxx; NMEA IDs 65-88
SAT_TYPE_GALILEO = 3 // GAxxx; NMEA IDs
SAT_TYPE_BEIDOU = 4 // GBxxx; NMEA IDs 201-235
SAT_TYPE_SBAS = 10 // NMEA IDs 33-54
)
type SatelliteInfo struct {
SatelliteNMEA uint8 // NMEA ID of the satellite. 1-32 is GPS, 33-54 is SBAS, 65-88 is Glonass.
SatelliteID string // Formatted code indicating source and PRN code. e.g. S138==WAAS satellite 138, G2==GPS satellites 2
Elevation int16 // Angle above local horizon, -xx to +90
Azimuth int16 // Bearing (degrees true), 0-359
Signal int8 // Signal strength, 0 - 99; -99 indicates no reception
Type uint8 // Type of satellite (GPS, GLONASS, Galileo, SBAS)
TimeLastSolution time.Time // Time (system ticker) a solution was last calculated using this satellite
TimeLastSeen time.Time // Time (system ticker) a signal was last received from this satellite
TimeLastTracked time.Time // Time (system ticker) this satellite was tracked (almanac data)
InSolution bool // True if satellite is used in the position solution (reported by GSA message or PUBX,03)
}
type SituationData struct {
// From GPS.
muGPS *sync.Mutex
muGPSPerformance *sync.Mutex
muSatellite *sync.Mutex
GPSLastFixSinceMidnightUTC float32
GPSLatitude float32
GPSLongitude float32
GPSFixQuality uint8
GPSHeightAboveEllipsoid float32 // GPS height above WGS84 ellipsoid, ft. This is specified by the GDL90 protocol, but most EFBs use MSL altitude instead. HAE is about 70-100 ft below GPS MSL altitude over most of the US.
GPSGeoidSep float32 // geoid separation, ft, MSL minus HAE (used in altitude calculation)
GPSSatellites uint16 // satellites used in solution
GPSSatellitesTracked uint16 // satellites tracked (almanac data received)
GPSSatellitesSeen uint16 // satellites seen (signal received)
GPSHorizontalAccuracy float32 // 95% confidence for horizontal position, meters.
GPSNACp uint8 // NACp categories are defined in AC 20-165A
GPSAltitudeMSL float32 // Feet MSL
GPSVerticalAccuracy float32 // 95% confidence for vertical position, meters
GPSVerticalSpeed float32 // GPS vertical velocity, feet per second
GPSLastFixLocalTime time.Time
GPSTrueCourse float32
GPSTurnRate float64 // calculated GPS rate of turn, degrees per second
GPSGroundSpeed float64
GPSLastGroundTrackTime time.Time
GPSTime time.Time
GPSLastGPSTimeStratuxTime time.Time // stratuxClock time since last GPS time received.
GPSLastValidNMEAMessageTime time.Time // time valid NMEA message last seen
GPSLastValidNMEAMessage string // last NMEA message processed.
GPSPositionSampleRate float64 // calculated sample rate of GPS positions
// From pressure sensor.
muBaro *sync.Mutex
BaroTemperature float32
BaroPressureAltitude float32
BaroVerticalSpeed float32
BaroLastMeasurementTime time.Time
// From AHRS source.
muAttitude *sync.Mutex
AHRSPitch float64
AHRSRoll float64
AHRSGyroHeading float64
AHRSMagHeading float64
AHRSSlipSkid float64
AHRSTurnRate float64
AHRSGLoad float64
AHRSGLoadMin float64
AHRSGLoadMax float64
AHRSLastAttitudeTime time.Time
AHRSStatus uint8
}
/*
myGPSPerfStats used to track short-term position / velocity trends, used to feed dynamic AHRS model. Use floats for better resolution of calculated data.
*/
type gpsPerfStats struct {
stratuxTime uint64 // time since Stratux start, msec
nmeaTime float32 // timestamp from NMEA message
msgType string // NMEA message type
gsf float32 // knots
coursef float32 // true course [degrees]
alt float32 // gps altitude, ft msl
vv float32 // vertical velocity, ft/sec
gpsTurnRate float64 // calculated turn rate, deg/sec. Right turn is positive.
gpsPitch float64 // estimated pitch angle, deg. Calculated from gps ground speed and VV. Equal to flight path angle.
gpsRoll float64 // estimated roll angle from turn rate and groundspeed, deg. Assumes airplane in coordinated turns.
gpsLoadFactor float64 // estimated load factor from turn rate and groundspeed, "gee". Assumes airplane in coordinated turns.
//TODO: valid/invalid flag.
}
var gpsPerf gpsPerfStats
var myGPSPerfStats []gpsPerfStats
var serialConfig *serial.Config
var serialPort *serial.Port
var readyToInitGPS bool //TODO: replace with channel control to terminate goroutine when complete
var Satellites map[string]SatelliteInfo
/*
u-blox5_Referenzmanual.pdf
Platform settings
Airborne <2g Recommended for typical airborne environment. No 2D position fixes supported.
p.91 - CFG-MSG
Navigation/Measurement Rate Settings
Header 0xB5 0x62
ID 0x06 0x08
0x0064 (100 ms)
0x0001
0x0001 (GPS time)
{0xB5, 0x62, 0x06, 0x08, 0x00, 0x64, 0x00, 0x01, 0x00, 0x01}
p.109 CFG-NAV5 (0x06 0x24)
Poll Navigation Engine Settings
*/
/*
chksumUBX()
returns the two-byte Fletcher algorithm checksum of byte array msg.
This is used in configuration messages for the u-blox GPS. See p. 97 of the
u-blox M8 Receiver Description.
*/
func chksumUBX(msg []byte) []byte {
ret := make([]byte, 2)
for i := 0; i < len(msg); i++ {
ret[0] = ret[0] + msg[i]
ret[1] = ret[1] + ret[0]
}
return ret
}
/*
makeUBXCFG()
creates a UBX-formatted package consisting of two sync characters,
class, ID, payload length in bytes (2-byte little endian), payload, and checksum.
See p. 95 of the u-blox M8 Receiver Description.
*/
func makeUBXCFG(class, id byte, msglen uint16, msg []byte) []byte {
ret := make([]byte, 6)
ret[0] = 0xB5
ret[1] = 0x62
ret[2] = class
ret[3] = id
ret[4] = byte(msglen & 0xFF)
ret[5] = byte((msglen >> 8) & 0xFF)
ret = append(ret, msg...)
chk := chksumUBX(ret[2:])
ret = append(ret, chk[0])
ret = append(ret, chk[1])
return ret
}
func makeNMEACmd(cmd string) []byte {
chk_sum := byte(0)
for i := range cmd {
chk_sum = chk_sum ^ byte(cmd[i])
}
return []byte(fmt.Sprintf("$%s*%02x\x0d\x0a", cmd, chk_sum))
}
func initGPSSerial() bool {
var device string
baudrate := int(9600)
isSirfIV := bool(false)
globalStatus.GPS_detected_type = 0 // reset detected type on each initialization
if _, err := os.Stat("/dev/ublox8"); err == nil { // u-blox 8 (RY83xAI over USB).
device = "/dev/ublox8"
globalStatus.GPS_detected_type = GPS_TYPE_UBX8
} else if _, err := os.Stat("/dev/ublox7"); err == nil { // u-blox 7 (VK-172, VK-162 Rev 2, RY725AI over USB).
device = "/dev/ublox7"
globalStatus.GPS_detected_type = GPS_TYPE_UBX7
} else if _, err := os.Stat("/dev/ublox6"); err == nil { // u-blox 6 (VK-162 Rev 1).
device = "/dev/ublox6"
globalStatus.GPS_detected_type = GPS_TYPE_UBX6
} else if _, err := os.Stat("/dev/prolific0"); err == nil { // Assume it's a BU-353-S4 SIRF IV.
//TODO: Check a "serialout" flag and/or deal with multiple prolific devices.
isSirfIV = true
baudrate = 4800
device = "/dev/prolific0"
globalStatus.GPS_detected_type = GPS_TYPE_PROLIFIC
} else if _, err := os.Stat("/dev/ttyAMA0"); err == nil { // ttyAMA0 is PL011 UART (GPIO pins 8 and 10) on all RPi.
device = "/dev/ttyAMA0"
globalStatus.GPS_detected_type = GPS_TYPE_UART
} else {
log.Printf("No suitable device found.\n")
return false
}
if globalSettings.DEBUG {
log.Printf("Using %s for GPS\n", device)
}
// Open port at default baud for config.
serialConfig = &serial.Config{Name: device, Baud: baudrate}
p, err := serial.OpenPort(serialConfig)
if err != nil {
log.Printf("serial port err: %s\n", err.Error())
return false
}
if isSirfIV {
log.Printf("Using SiRFIV config.\n")
// Enable 38400 baud.
p.Write(makeNMEACmd("PSRF100,1,38400,8,1,0"))
baudrate = 38400
p.Close()
time.Sleep(250 * time.Millisecond)
// Re-open port at newly configured baud so we can configure 5Hz messages.
serialConfig = &serial.Config{Name: device, Baud: baudrate}
p, err = serial.OpenPort(serialConfig)
// Enable 5Hz. (To switch back to 1Hz: $PSRF103,00,7,00,0*22)
p.Write(makeNMEACmd("PSRF103,00,6,00,0"))
// Enable GGA.
p.Write(makeNMEACmd("PSRF103,00,00,01,01"))
// Enable GSA.
p.Write(makeNMEACmd("PSRF103,02,00,01,01"))
// Enable RMC.
p.Write(makeNMEACmd("PSRF103,04,00,01,01"))
// Enable VTG.
p.Write(makeNMEACmd("PSRF103,05,00,01,01"))
// Enable GSV (once every 5 position updates)
p.Write(makeNMEACmd("PSRF103,03,00,05,01"))
if globalSettings.DEBUG {
log.Printf("Finished writing SiRF GPS config to %s. Opening port to test connection.\n", device)
}
} else {
// Byte order for UBX configuration is little endian.
// Set 10 Hz update to make gpsattitude more responsive for ublox7.
updatespeed := []byte{0x64, 0x00, 0x01, 0x00, 0x01, 0x00} // 10 Hz
// Set navigation settings.
nav := make([]byte, 36)
nav[0] = 0x05 // Set dyn and fixMode only.
nav[1] = 0x00
// dyn.
nav[2] = 0x07 // "Airborne with >2g Acceleration".
nav[3] = 0x02 // 3D only.
p.Write(makeUBXCFG(0x06, 0x24, 36, nav))
// Turn off "time pulse" (usually drives an LED).
tp5 := make([]byte, 32)
tp5[4] = 0x32
tp5[8] = 0x40
tp5[9] = 0x42
tp5[10] = 0x0F
tp5[12] = 0x40
tp5[13] = 0x42
tp5[14] = 0x0F
tp5[28] = 0xE7
p.Write(makeUBXCFG(0x06, 0x31, 32, tp5))
// GNSS configuration CFG-GNSS for ublox 7 higher, p. 125 (v8)
// Notes: ublox8 is multi-GNSS capable (simultaneous decoding of GPS and GLONASS, or
// GPS and Galileo) if SBAS (e.g. WAAS) is unavailable. This may provide robustness
// against jamming / interference on one set of frequencies. However, this will drop the
// position reporting rate to 5 Hz during times multi-GNSS is in use. This shouldn't affect
// gpsattitude too much -- without WAAS corrections, the algorithm could get jumpy at higher
// sampling rates.
cfgGnss := []byte{0x00, 0x20, 0x20, 0x06}
gps := []byte{0x00, 0x08, 0x10, 0x00, 0x01, 0x00, 0x01, 0x01} // enable GPS with 8-16 tracking channels
sbas := []byte{0x01, 0x02, 0x03, 0x00, 0x01, 0x00, 0x01, 0x01} // enable SBAS (WAAS) with 2-3 tracking channels
beidou := []byte{0x03, 0x00, 0x10, 0x00, 0x00, 0x00, 0x01, 0x01}
qzss := []byte{0x05, 0x00, 0x03, 0x00, 0x00, 0x00, 0x01, 0x01}
glonass := []byte{0x06, 0x04, 0x0E, 0x00, 0x00, 0x00, 0x01, 0x01} // this disables GLONASS
galileo := []byte{0x02, 0x04, 0x08, 0x00, 0x00, 0x00, 0x01, 0x01} // this disables Galileo
//if (globalStatus.GPS_detected_type == GPS_TYPE_UBX8) || (globalStatus.GPS_detected_type == GPS_TYPE_UART) { // assume that any GPS connected to serial GPIO is ublox8 (RY835/6AI)
//log.Printf("UBX8 device detected on USB, or GPS serial connection in use. Attempting GLONASS and Galelio configuration.\n")
// glonass = []byte{0x06, 0x08, 0x0E, 0x00, 0x01, 0x00, 0x01, 0x01} // this enables GLONASS with 8-14 tracking channels
// galileo = []byte{0x02, 0x04, 0x08, 0x00, 0x01, 0x00, 0x01, 0x01} // this enables Galileo with 4-8 tracking channels
// updatespeed = []byte{0x06, 0x00, 0xF4, 0x01, 0x01, 0x00} // Nav speed 2Hz
// }
cfgGnss = append(cfgGnss, gps...)
cfgGnss = append(cfgGnss, sbas...)
cfgGnss = append(cfgGnss, beidou...)
cfgGnss = append(cfgGnss, qzss...)
cfgGnss = append(cfgGnss, glonass...)
cfgGnss = append(cfgGnss, galileo...)
p.Write(makeUBXCFG(0x06, 0x3E, uint16(len(cfgGnss)), cfgGnss))
// SBAS configuration for ublox 6 and higher
p.Write(makeUBXCFG(0x06, 0x16, 8, []byte{0x01, 0x07, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00}))
//Navigation Rate 10Hz for <= UBX7 2Hz for UBX8
p.Write(makeUBXCFG(0x06, 0x08, 6, updatespeed))
// Message output configuration: UBX,00 (position) on each calculated fix; UBX,03 (satellite info) every 5th fix,
// UBX,04 (timing) every 10th, GGA (NMEA position) every 5th. All other NMEA messages disabled.
// Msg DDC UART1 UART2 USB I2C Res
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x00, 0x00, 0x05, 0x00, 0x05, 0x00, 0x01})) // GGA enabled every 5th message
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01})) // GLL disabled
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01})) // GSA disabled
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01})) // GSV disabled
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01})) // RMC
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x05, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01})) // VGT
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})) // GRS
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})) // GST
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})) // ZDA
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x09, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})) // GBS
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x0A, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})) // DTM
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x0D, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})) // GNS
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x0E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})) // ???
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF0, 0x0F, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00})) // VLW
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF1, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00})) // Ublox,0
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF1, 0x03, 0x00, 0x05, 0x00, 0x05, 0x00, 0x00})) // Ublox,3
p.Write(makeUBXCFG(0x06, 0x01, 8, []byte{0xF1, 0x04, 0x00, 0x0A, 0x00, 0x0A, 0x00, 0x00})) // Ublox,4
// Reconfigure serial port.
cfg := make([]byte, 20)
cfg[0] = 0x01 // portID.
cfg[1] = 0x00 // res0.
cfg[2] = 0x00 // res1.
cfg[3] = 0x00 // res1.
// [ 7 ] [ 6 ] [ 5 ] [ 4 ]
// 0000 0000 0000 0000 0000 10x0 1100 0000
// UART mode. 0 stop bits, no parity, 8 data bits. Little endian order.
cfg[4] = 0xC0
cfg[5] = 0x08
cfg[6] = 0x00
cfg[7] = 0x00
// Baud rate. Little endian order.
bdrt := uint32(38400)
cfg[11] = byte((bdrt >> 24) & 0xFF)
cfg[10] = byte((bdrt >> 16) & 0xFF)
cfg[9] = byte((bdrt >> 8) & 0xFF)
cfg[8] = byte(bdrt & 0xFF)
// inProtoMask. NMEA and UBX. Little endian.
cfg[12] = 0x03
cfg[13] = 0x00
// outProtoMask. NMEA. Little endian.
cfg[14] = 0x02
cfg[15] = 0x00
cfg[16] = 0x00 // flags.
cfg[17] = 0x00 // flags.
cfg[18] = 0x00 //pad.
cfg[19] = 0x00 //pad.
p.Write(makeUBXCFG(0x06, 0x00, 20, cfg))
// time.Sleep(100* time.Millisecond) // pause and wait for the GPS to finish configuring itself before closing / reopening the port
baudrate = 38400
if globalSettings.DEBUG {
log.Printf("Finished writing u-blox GPS config to %s. Opening port to test connection.\n", device)
}
}
p.Close()
time.Sleep(250 * time.Millisecond)
// Re-open port at newly configured baud so we can read messages. ReadTimeout is set to keep from blocking the gpsSerialReader() on misconfigures or ttyAMA disconnects
serialConfig = &serial.Config{Name: device, Baud: baudrate, ReadTimeout: time.Millisecond * 2500}
p, err = serial.OpenPort(serialConfig)
if err != nil {
log.Printf("serial port err: %s\n", err.Error())
return false
}
serialPort = p
return true
}
// func validateNMEAChecksum determines if a string is a properly formatted NMEA sentence with a valid checksum.
//
// If the input string is valid, output is the input stripped of the "$" token and checksum, along with a boolean 'true'
// If the input string is the incorrect format, the checksum is missing/invalid, or checksum calculation fails, an error string and
// boolean 'false' are returned
//
// Checksum is calculated as XOR of all bytes between "$" and "*"
func validateNMEAChecksum(s string) (string, bool) {
//validate format. NMEA sentences start with "$" and end in "*xx" where xx is the XOR value of all bytes between
if !(strings.HasPrefix(s, "$") && strings.Contains(s, "*")) {
return "Invalid NMEA message", false
}
// strip leading "$" and split at "*"
s_split := strings.Split(strings.TrimPrefix(s, "$"), "*")
s_out := s_split[0]
s_cs := s_split[1]
if len(s_cs) < 2 {
return "Missing checksum. Fewer than two bytes after asterisk", false
}
cs, err := strconv.ParseUint(s_cs[:2], 16, 8)
if err != nil {
return "Invalid checksum", false
}
cs_calc := byte(0)
for i := range s_out {
cs_calc = cs_calc ^ byte(s_out[i])
}
if cs_calc != byte(cs) {
return fmt.Sprintf("Checksum failed. Calculated %#X; expected %#X", cs_calc, cs), false
}
return s_out, true
}
// Only count this heading if a "sustained" >7 kts is obtained. This filters out a lot of heading
// changes while on the ground and "movement" is really only changes in GPS fix as it settles down.
//TODO: Some more robust checking above current and last speed.
//TODO: Dynamic adjust for gain based on groundspeed
func setTrueCourse(groundSpeed uint16, trueCourse float64) {
if mySituation.GPSGroundSpeed >= 7 && groundSpeed >= 7 {
// This was previously used to filter small ground speed spikes caused by GPS position drift.
// It was passed to the previous AHRS heading calculator. Currently unused, maybe in the future it will be.
_ = trueCourse
_ = groundSpeed
}
}
/*
calcGPSAttitude estimates turn rate, pitch, and roll based on recent GPS groundspeed, track, and altitude / vertical speed.
Method uses stored performance statistics from myGPSPerfStats[]. Ideally, calculation is based on most recent 1.5 seconds of data,
assuming 10 Hz sampling frequency. Lower frequency sample rates will increase calculation window for smoother response, at the
cost of slightly increased lag.
(c) 2016 Keith Tschohl. All rights reserved.
Distributable under the terms of the "BSD-New" License that can be found in
the LICENSE file, herein included as part of this header.
*/
func calcGPSAttitude() bool {
// check slice length. Return error if empty set or set zero values
mySituation.muGPSPerformance.Lock()
defer mySituation.muGPSPerformance.Unlock()
length := len(myGPSPerfStats)
index := length - 1
if length == 0 {
log.Printf("GPS attitude: No data received yet. Not calculating attitude.\n")
return false
} else if length == 1 {
//log.Printf("myGPSPerfStats has one data point. Setting statistics to zero.\n")
myGPSPerfStats[index].gpsTurnRate = 0
myGPSPerfStats[index].gpsPitch = 0
myGPSPerfStats[index].gpsRoll = 0
return false
}
// check if GPS data was put in the structure more than three seconds ago -- this shouldn't happen unless something is wrong.
if (stratuxClock.Milliseconds - myGPSPerfStats[index].stratuxTime) > 3000 {
myGPSPerfStats[index].gpsTurnRate = 0
myGPSPerfStats[index].gpsPitch = 0
myGPSPerfStats[index].gpsRoll = 0
log.Printf("GPS attitude: GPS data is more than three seconds old. Setting attitude to zero.\n")
return false
}
// check time interval between samples
t1 := myGPSPerfStats[index].nmeaTime
t0 := myGPSPerfStats[index-1].nmeaTime
dt := t1 - t0
// first time error case: index is more than three seconds ahead of index-1
if dt > 3 {
log.Printf("GPS attitude: Can't calculate GPS attitude. Reference data is old. dt = %v\n", dt)
return false
}
// second case: index is behind index-1. This could be result of day rollover. If time is within n seconds of UTC,
// we rebase to the previous day, and will re-rebase the entire slice forward to the current day once all values roll over.
//TODO: Validate by testing at 0000Z
if dt < 0 {
log.Printf("GPS attitude: Current GPS time (%.2f) is older than last GPS time (%.2f). Checking for 0000Z rollover.\n", t1, t0)
if myGPSPerfStats[index-1].nmeaTime > 86300 && myGPSPerfStats[index].nmeaTime < 100 { // be generous with the time window at rollover
myGPSPerfStats[index].nmeaTime += 86400
} else {
// time decreased, but not due to a recent rollover. Something odd is going on.
log.Printf("GPS attitude: Time isn't near 0000Z. Unknown reason for offset. Can't calculate GPS attitude.\n")
return false
}
// check time array to see if all timestamps are > 86401 seconds since midnight
var tempTime []float64
tempTime = make([]float64, length, length)
for i := 0; i < length; i++ {
tempTime[i] = float64(myGPSPerfStats[i].nmeaTime)
}
minTime, _ := arrayMin(tempTime)
if minTime > 86401.0 {
log.Printf("GPS attitude: Rebasing GPS time since midnight to current day.\n")
for i := 0; i < length; i++ {
myGPSPerfStats[i].nmeaTime -= 86400
}
}
// Verify adjustment
dt = myGPSPerfStats[index].nmeaTime - myGPSPerfStats[index-1].nmeaTime
log.Printf("GPS attitude: New dt = %f\n", dt)
if dt > 3 {
log.Printf("GPS attitude: Can't calculate GPS attitude. Reference data is old. dt = %v\n", dt)
return false
} else if dt < 0 {
log.Printf("GPS attitude: Something went wrong rebasing the time.\n")
return false
}
}
// If all of the bounds checks pass, begin processing the GPS data.
// local variables
var headingAvg, dh, v_x, v_z, a_c, omega, slope, intercept, dt_avg float64
var tempHdg, tempHdgUnwrapped, tempHdgTime, tempSpeed, tempVV, tempSpeedTime, tempRegWeights []float64 // temporary arrays for regression calculation
var valid bool
var lengthHeading, lengthSpeed int
var halfwidth float64 // width of regression evaluation window. Minimum of 1.5 seconds and maximum of 3.5 seconds.
center := float64(myGPSPerfStats[index].nmeaTime) // current time for calculating regression weights
// frequency detection
tempSpeedTime = make([]float64, 0)
for i := 1; i < length; i++ {
dt = myGPSPerfStats[i].nmeaTime - myGPSPerfStats[i-1].nmeaTime
if dt > 0.05 { // avoid double counting messages with same / similar timestamps
tempSpeedTime = append(tempSpeedTime, float64(dt))
}
}
//log.Printf("Delta time array is %v.\n",tempSpeedTime)
dt_avg, valid = mean(tempSpeedTime)
if valid && dt_avg > 0 {
if globalSettings.DEBUG {
log.Printf("GPS attitude: Average delta time is %.2f s (%.1f Hz)\n", dt_avg, 1/dt_avg)
}
halfwidth = 9 * dt_avg
mySituation.GPSPositionSampleRate = 1 / dt_avg
} else {
if globalSettings.DEBUG {
log.Printf("GPS attitude: Couldn't determine sample rate\n")
}
halfwidth = 3.5
mySituation.GPSPositionSampleRate = 0
}
if halfwidth > 3.5 {
halfwidth = 3.5 // limit calculation window to 3.5 seconds of data for 1 Hz or slower samples
} else if halfwidth < 1.5 {
halfwidth = 1.5 // use minimum of 1.5 seconds for sample rates faster than 5 Hz
}
if (globalStatus.GPS_detected_type & 0xf0) == GPS_PROTOCOL_UBX { // UBX reports vertical speed, so we can just walk through all of the PUBX messages in order
// Speed and VV. Use all values in myGPSPerfStats; perform regression.
tempSpeedTime = make([]float64, length, length) // all are length of original slice
tempSpeed = make([]float64, length, length)
tempVV = make([]float64, length, length)
tempRegWeights = make([]float64, length, length)
for i := 0; i < length; i++ {
tempSpeed[i] = float64(myGPSPerfStats[i].gsf)
tempVV[i] = float64(myGPSPerfStats[i].vv)
tempSpeedTime[i] = float64(myGPSPerfStats[i].nmeaTime)
tempRegWeights[i] = triCubeWeight(center, halfwidth, tempSpeedTime[i])
}
// Groundspeed regression estimate.
slope, intercept, valid = linRegWeighted(tempSpeedTime, tempSpeed, tempRegWeights)
if !valid {
log.Printf("GPS attitude: Error calculating speed regression from UBX position messages")
return false
} else {
v_x = (slope*float64(myGPSPerfStats[index].nmeaTime) + intercept) * 1.687810 // units are knots, converted to feet/sec
}
// Vertical speed regression estimate.
slope, intercept, valid = linRegWeighted(tempSpeedTime, tempVV, tempRegWeights)
if !valid {
log.Printf("GPS attitude: Error calculating vertical speed regression from UBX position messages")
return false
} else {
v_z = (slope*float64(myGPSPerfStats[index].nmeaTime) + intercept) // units are feet per sec; no conversion needed
}
} else { // If we need to parse standard NMEA messages, determine if it's RMC or GGA, then fill the temporary slices accordingly. Need to pull from multiple message types since GGA doesn't do course or speed; VTG / RMC don't do altitude, etc. Grrr.
//v_x = float64(myGPSPerfStats[index].gsf * 1.687810)
//v_z = 0
// first, parse groundspeed from RMC messages.
tempSpeedTime = make([]float64, 0)
tempSpeed = make([]float64, 0)
tempRegWeights = make([]float64, 0)
for i := 0; i < length; i++ {
if myGPSPerfStats[i].msgType == "GPRMC" || myGPSPerfStats[i].msgType == "GNRMC" {
tempSpeed = append(tempSpeed, float64(myGPSPerfStats[i].gsf))
tempSpeedTime = append(tempSpeedTime, float64(myGPSPerfStats[i].nmeaTime))
tempRegWeights = append(tempRegWeights, triCubeWeight(center, halfwidth, float64(myGPSPerfStats[i].nmeaTime)))
}
}
lengthSpeed = len(tempSpeed)
if lengthSpeed == 0 {
log.Printf("GPS Attitude: No groundspeed data could be parsed from NMEA RMC messages\n")
return false
} else if lengthSpeed == 1 {
v_x = tempSpeed[0] * 1.687810
} else {
slope, intercept, valid = linRegWeighted(tempSpeedTime, tempSpeed, tempRegWeights)
if !valid {
log.Printf("GPS attitude: Error calculating speed regression from NMEA RMC position messages")
return false
} else {
v_x = (slope*float64(myGPSPerfStats[index].nmeaTime) + intercept) * 1.687810 // units are knots, converted to feet/sec
//log.Printf("Avg speed %f calculated from %d RMC messages\n", v_x, lengthSpeed) // DEBUG
}
}
// next, calculate vertical velocity from GGA altitude data.
tempSpeedTime = make([]float64, 0)
tempVV = make([]float64, 0)
tempRegWeights = make([]float64, 0)
for i := 0; i < length; i++ {
if myGPSPerfStats[i].msgType == "GPGGA" || myGPSPerfStats[i].msgType == "GNGGA" {
tempVV = append(tempVV, float64(myGPSPerfStats[i].alt))
tempSpeedTime = append(tempSpeedTime, float64(myGPSPerfStats[i].nmeaTime))
tempRegWeights = append(tempRegWeights, triCubeWeight(center, halfwidth, float64(myGPSPerfStats[i].nmeaTime)))
}
}
lengthSpeed = len(tempVV)
if lengthSpeed < 2 {
log.Printf("GPS Attitude: Not enough points to calculate vertical speed from NMEA GGA messages\n")
return false
} else {
slope, _, valid = linRegWeighted(tempSpeedTime, tempVV, tempRegWeights)
if !valid {
log.Printf("GPS attitude: Error calculating vertical speed regression from NMEA GGA messages")
return false
} else {
v_z = slope // units are feet/sec
//log.Printf("Avg VV %f calculated from %d GGA messages\n", v_z, lengthSpeed) // DEBUG
}
}
}
// If we're going too slow for processNMEALine() to give us valid heading data, there's no sense in trying to parse it.
// However, we need to return a valid level attitude so we don't get the "red X of death" on our AHRS display.
// This will also eliminate most of the nuisance error message from the turn rate calculation.
if v_x < 6 { // ~3.55 knots
myGPSPerfStats[index].gpsPitch = 0
myGPSPerfStats[index].gpsRoll = 0
myGPSPerfStats[index].gpsTurnRate = 0
myGPSPerfStats[index].gpsLoadFactor = 1.0
mySituation.GPSTurnRate = 0
// Output format:GPSAtttiude,seconds,nmeaTime,msg_type,GS,Course,Alt,VV,filtered_GS,filtered_course,turn rate,filtered_vv,pitch, roll,load_factor
buf := fmt.Sprintf("GPSAttitude,%.1f,%.2f,%s,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f\n", float64(stratuxClock.Milliseconds)/1000, myGPSPerfStats[index].nmeaTime, myGPSPerfStats[index].msgType, myGPSPerfStats[index].gsf, myGPSPerfStats[index].coursef, myGPSPerfStats[index].alt, myGPSPerfStats[index].vv, v_x/1.687810, headingAvg, myGPSPerfStats[index].gpsTurnRate, v_z, myGPSPerfStats[index].gpsPitch, myGPSPerfStats[index].gpsRoll, myGPSPerfStats[index].gpsLoadFactor)
if globalSettings.DEBUG {
log.Printf("%s", buf) // FIXME. Send to sqlite log or other file?
}
logGPSAttitude(myGPSPerfStats[index])
//replayLog(buf, MSGCLASS_AHRS)
return true
}
// Heading. Same method used for UBX and generic.
// First, walk through the PerfStats and parse only valid heading data.
//log.Printf("Raw heading data:")
for i := 0; i < length; i++ {
//log.Printf("%.1f,",myGPSPerfStats[i].coursef)
if myGPSPerfStats[i].coursef >= 0 { // negative values are used to flag invalid / unavailable course
tempHdg = append(tempHdg, float64(myGPSPerfStats[i].coursef))
tempHdgTime = append(tempHdgTime, float64(myGPSPerfStats[i].nmeaTime))
}
}
//log.Printf("\n")
//log.Printf("tempHdg: %v\n", tempHdg)
// Next, unwrap the heading so we don't mess up the regression by fitting a line across the 0/360 deg discontinuity.
lengthHeading = len(tempHdg)
tempHdgUnwrapped = make([]float64, lengthHeading, lengthHeading)
tempRegWeights = make([]float64, lengthHeading, lengthHeading)
if lengthHeading > 1 {
tempHdgUnwrapped[0] = tempHdg[0]
tempRegWeights[0] = triCubeWeight(center, halfwidth, tempHdgTime[0])
for i := 1; i < lengthHeading; i++ {
tempRegWeights[i] = triCubeWeight(center, halfwidth, tempHdgTime[i])
if math.Abs(tempHdg[i]-tempHdg[i-1]) < 180 { // case 1: if angle change is less than 180 degrees, use the same reference system
tempHdgUnwrapped[i] = tempHdgUnwrapped[i-1] + tempHdg[i] - tempHdg[i-1]
} else if tempHdg[i] > tempHdg[i-1] { // case 2: heading has wrapped around from NE to NW. Subtract 360 to keep consistent with previous data.
tempHdgUnwrapped[i] = tempHdgUnwrapped[i-1] + tempHdg[i] - tempHdg[i-1] - 360
} else { // case 3: heading has wrapped around from NW to NE. Add 360 to keep consistent with previous data.
tempHdgUnwrapped[i] = tempHdgUnwrapped[i-1] + tempHdg[i] - tempHdg[i-1] + 360
}
}
} else { //
if globalSettings.DEBUG {
log.Printf("GPS attitude: Can't calculate turn rate with less than two points.\n")
}
return false
}
// Finally, calculate turn rate as the slope of the weighted linear regression of unwrapped heading.
slope, intercept, valid = linRegWeighted(tempHdgTime, tempHdgUnwrapped, tempRegWeights)
if !valid {
log.Printf("GPS attitude: Regression error calculating turn rate")
return false
} else {
headingAvg = slope*float64(myGPSPerfStats[index].nmeaTime) + intercept
dh = slope // units are deg per sec; no conversion needed here
//log.Printf("Calculated heading and turn rate: %.3f degrees, %.3f deg/sec\n",headingAvg,dh)
}
myGPSPerfStats[index].gpsTurnRate = dh
mySituation.GPSTurnRate = dh
// pitch angle -- or to be more pedantic, glide / climb angle, since we're just looking a rise-over-run.
// roll angle, based on turn rate and ground speed. Only valid for coordinated flight. Differences between airspeed and groundspeed will trip this up.
if v_x > 20 { // reduce nuisance 'bounce' at low speeds. 20 ft/sec = 11.9 knots.
myGPSPerfStats[index].gpsPitch = math.Atan2(v_z, v_x) * 180.0 / math.Pi
/*
Governing equations for roll calculations
Physics tells us that
a_z = g (in steady-state flight -- climbing, descending, or level -- this is gravity. 9.81 m/s^2 or 32.2 ft/s^2)
a_c = v^2/r (centripetal acceleration)
We don't know r. However, we do know the tangential velocity (v) and angular velocity (omega). Express omega in radians per unit time, and
v = omega*r
By substituting and rearranging terms:
a_c = v^2 / (v / omega)
a_c = v*omega
Free body diagram time!
/|
a_r / | a_z
/__|
X a_c
\_________________ [For the purpose of this comment, " X" is an airplane in a 20 degree bank. Use your imagination, mkay?)
Resultant acceleration a_r is what the wings feel; a_r/a_z = load factor. Anyway, trig out the bank angle:
bank angle = atan(a_c/a_z)
= atan(v*omega/g)
wing loading = sqrt(a_c^2 + a_z^2) / g
*/
g := 32.174 // ft/(s^2)
omega = radians(myGPSPerfStats[index].gpsTurnRate) // need radians/sec
a_c = v_x * omega
myGPSPerfStats[index].gpsRoll = math.Atan2(a_c, g) * 180 / math.Pi // output is degrees
myGPSPerfStats[index].gpsLoadFactor = math.Sqrt(a_c*a_c+g*g) / g
} else {
myGPSPerfStats[index].gpsPitch = 0
myGPSPerfStats[index].gpsRoll = 0
myGPSPerfStats[index].gpsLoadFactor = 1
}
if globalSettings.DEBUG {
// Output format:GPSAtttiude,seconds,nmeaTime,msg_type,GS,Course,Alt,VV,filtered_GS,filtered_course,turn rate,filtered_vv,pitch, roll,load_factor
buf := fmt.Sprintf("GPSAttitude,%.1f,%.2f,%s,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f,%0.3f\n", float64(stratuxClock.Milliseconds)/1000, myGPSPerfStats[index].nmeaTime, myGPSPerfStats[index].msgType, myGPSPerfStats[index].gsf, myGPSPerfStats[index].coursef, myGPSPerfStats[index].alt, myGPSPerfStats[index].vv, v_x/1.687810, headingAvg, myGPSPerfStats[index].gpsTurnRate, v_z, myGPSPerfStats[index].gpsPitch, myGPSPerfStats[index].gpsRoll, myGPSPerfStats[index].gpsLoadFactor)
log.Printf("%s", buf) // FIXME. Send to sqlite log or other file?
}
logGPSAttitude(myGPSPerfStats[index])
//replayLog(buf, MSGCLASS_AHRS)
return true
}
func calculateNACp(accuracy float32) uint8 {
ret := uint8(0)
if accuracy < 3 {
ret = 11
} else if accuracy < 10 {
ret = 10
} else if accuracy < 30 {
ret = 9
} else if accuracy < 92.6 {
ret = 8
} else if accuracy < 185.2 {
ret = 7
} else if accuracy < 555.6 {
ret = 6
}
return ret
}
/*
registerSituationUpdate().
Called whenever there is a change in mySituation.
*/
func registerSituationUpdate() {
logSituation()
situationUpdate.SendJSON(mySituation)
}
/*
processNMEALine parses NMEA-0183 formatted strings against several message types.
Standard messages supported: RMC GGA VTG GSA
U-blox proprietary messages: PUBX,00 PUBX,03 PUBX,04
return is false if errors occur during parse, or if GPS position is invalid
return is true if parse occurs correctly and position is valid.
*/
func processNMEALine(l string) (sentenceUsed bool) {
mySituation.muGPS.Lock()
defer func() {
if sentenceUsed || globalSettings.DEBUG {
registerSituationUpdate()
}
mySituation.muGPS.Unlock()
}()
// Local variables for GPS attitude estimation
thisGpsPerf := gpsPerf // write to myGPSPerfStats at end of function IFF
thisGpsPerf.coursef = -999.9 // default value of -999.9 indicates invalid heading to regression calculation
thisGpsPerf.stratuxTime = stratuxClock.Milliseconds // used for gross indexing
updateGPSPerf := false // change to true when position or vector info is read
l_valid, validNMEAcs := validateNMEAChecksum(l)
if !validNMEAcs {
log.Printf("GPS error. Invalid NMEA string: %s\n", l_valid) // remove log message once validation complete
return false
}
x := strings.Split(l_valid, ",")
mySituation.GPSLastValidNMEAMessageTime = stratuxClock.Time
mySituation.GPSLastValidNMEAMessage = l
if x[0] == "PUBX" { // UBX proprietary message
if x[1] == "00" { // Position fix.
if len(x) < 20 {
return false
}
// set the global GPS type to UBX as soon as we see our first (valid length)
// PUBX,01 position message, even if we don't have a fix
if (globalStatus.GPS_detected_type & 0xf0) != GPS_PROTOCOL_UBX {
globalStatus.GPS_detected_type |= GPS_PROTOCOL_UBX
log.Printf("GPS detected: u-blox NMEA position message seen.\n")
}
thisGpsPerf.msgType = x[0] + x[1]
tmpSituation := mySituation // If we decide to not use the data in this message, then don't make incomplete changes in mySituation.
// Do the accuracy / quality fields first to prevent invalid position etc. from being sent downstream
// field 8 = nav status
// DR = dead reckoning, G2= 2D GPS, G3 = 3D GPS, D2= 2D diff, D3 = 3D diff, RK = GPS+DR, TT = time only
if x[8] == "D2" || x[8] == "D3" {
tmpSituation.GPSFixQuality = 2
} else if x[8] == "G2" || x[8] == "G3" {
tmpSituation.GPSFixQuality = 1
} else if x[8] == "DR" || x[8] == "RK" {
tmpSituation.GPSFixQuality = 6
} else if x[8] == "NF" {
tmpSituation.GPSFixQuality = 0 // Just a note.
return false
} else {
tmpSituation.GPSFixQuality = 0 // Just a note.
return false
}
// field 9 = horizontal accuracy, m
hAcc, err := strconv.ParseFloat(x[9], 32)
if err != nil {
return false
}
tmpSituation.GPSHorizontalAccuracy = float32(hAcc * 2) // UBX reports 1-sigma variation; NACp is 95% confidence (2-sigma)
// NACp estimate.
tmpSituation.GPSNACp = calculateNACp(tmpSituation.GPSHorizontalAccuracy)
// field 10 = vertical accuracy, m
/*
vAcc, err := strconv.ParseFloat(x[10], 32)
if err != nil {
return false
}
tmpSituation.GPSVerticalAccuracy = float32(vAcc * 2) // UBX reports 1-sigma variation; we want 95% confidence
*/
tmpSituation.GPSVerticalAccuracy = float32(2.) * tmpSituation.GPSHorizontalAccuracy
// field 2 = time
if len(x[2]) < 8 {
return false
}
hr, err1 := strconv.Atoi(x[2][0:2])
min, err2 := strconv.Atoi(x[2][2:4])
sec, err3 := strconv.ParseFloat(x[2][4:], 32)
if err1 != nil || err2 != nil || err3 != nil {
return false
}
tmpSituation.GPSLastFixSinceMidnightUTC = float32(3600*hr+60*min) + float32(sec)
thisGpsPerf.nmeaTime = tmpSituation.GPSLastFixSinceMidnightUTC
// field 3-4 = lat
if len(x[3]) < 10 {
return false
}
hr, err1 = strconv.Atoi(x[3][0:2])
minf, err2 := strconv.ParseFloat(x[3][2:], 32)
if err1 != nil || err2 != nil {
return false
}
tmpSituation.GPSLatitude = float32(hr) + float32(minf/60.0)
if x[4] == "S" { // South = negative.
tmpSituation.GPSLatitude = -tmpSituation.GPSLatitude
}
// field 5-6 = lon
if len(x[5]) < 11 {
return false
}
hr, err1 = strconv.Atoi(x[5][0:3])
minf, err2 = strconv.ParseFloat(x[5][3:], 32)
if err1 != nil || err2 != nil {
return false
}
tmpSituation.GPSLongitude = float32(hr) + float32(minf/60.0)
if x[6] == "W" { // West = negative.
tmpSituation.GPSLongitude = -tmpSituation.GPSLongitude
}
// field 7 = height above ellipsoid, m
hae, err1 := strconv.ParseFloat(x[7], 32)
if err1 != nil {
return false
}
// the next 'if' statement is a workaround for a ubx7 firmware bug:
// PUBX,00 reports HAE with a floor of zero (i.e. negative altitudes are set to zero). This causes GPS altitude to never read lower than -GPSGeoidSep,
// placing minimum GPS altitude at about +80' MSL over most of North America.
//
// This does not affect GGA messages, so we can just rely on GGA to set altitude in these cases. It's a slower (1 Hz vs 5 Hz / 10 Hz), less precise
// (0.1 vs 0.001 mm resolution) report, but in practice the accuracy never gets anywhere near this resolution, so this should be an acceptable tradeoff
if hae != 0 {
alt := float32(hae*3.28084) - tmpSituation.GPSGeoidSep // convert to feet and offset by geoid separation