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libgpsd_core.c
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/* libgpsd_core.c -- manage access to sensors
*
* Access to the driver layer goes through the entry points in this file.
* The idea is to present a session as an abstraction from which you get
* fixes (and possibly other data updates) by calling gpsd_multipoll(). The
* rest is setup and teardown. (For backward compatibility the older gpsd_poll()
* entry point has been retained.)
*
* This file is Copyright (c) 2010 by the GPSD project
* SPDX-License-Identifier: BSD-2-clause
*/
#ifdef __linux__
/* FreeBSD chokes on this */
/* getsid() needs _XOPEN_SOURCE, 500 means X/Open 1995 */
#define _XOPEN_SOURCE 500
/* isfinite() and pselect() needs _POSIX_C_SOURCE >= 200112L */
#define _POSIX_C_SOURCE 200112L
#endif /* __linux__ */
/* strlcpy() needs _DARWIN_C_SOURCE */
#define _DARWIN_C_SOURCE
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <libgen.h>
#include <math.h>
#include <string.h>
#include <stdarg.h>
#include <fcntl.h>
#include <ctype.h>
#include <syslog.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/select.h>
#include <sys/stat.h>
#include <assert.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <unistd.h>
#include "gpsd.h"
#include "matrix.h"
#include "strfuncs.h"
#if defined(NMEA2000_ENABLE)
#include "driver_nmea2000.h"
#endif /* defined(NMEA2000_ENABLE) */
#if defined(PDS_ENABLE)
#include "driver_pds.h"
#endif /* defined(PDS_ENABLE) */
ssize_t gpsd_write(struct gps_device_t *session,
const char *buf,
const size_t len)
/* pass low-level data to devices straight through */
{
return session->context->serial_write(session, buf, len);
}
static void basic_report(const char *buf)
{
(void)fputs(buf, stderr);
}
void errout_reset(struct gpsd_errout_t *errout)
{
errout->debug = LOG_SHOUT;
errout->report = basic_report;
}
#if defined(PPS_ENABLE)
static pthread_mutex_t report_mutex;
void gpsd_acquire_reporting_lock(void)
{
int err;
err = pthread_mutex_lock(&report_mutex);
if ( 0 != err ) {
/* POSIX says pthread_mutex_lock() should only fail if the
thread holding the lock has died. Best for gppsd to just die
because things are FUBAR. */
(void) fprintf(stderr,"pthread_mutex_lock() failed: %s\n",
strerror(errno));
exit(EXIT_FAILURE);
}
}
void gpsd_release_reporting_lock(void)
{
int err;
err = pthread_mutex_unlock(&report_mutex);
if ( 0 != err ) {
/* POSIX says pthread_mutex_unlock() should only fail when
trying to unlock a lock that does not exist, or is not owned by
this thread. This should never happen, so best for gpsd to die
because things are FUBAR. */
(void) fprintf(stderr,"pthread_mutex_unlock() failed: %s\n",
strerror(errno));
exit(EXIT_FAILURE);
}
}
#endif /* PPS_ENABLE */
#ifndef SQUELCH_ENABLE
static void visibilize(char *outbuf, size_t outlen,
const char *inbuf, size_t inlen)
{
const char *sp;
outbuf[0] = '\0';
for (sp = inbuf; sp < inbuf + inlen && strlen(outbuf)+6 < outlen; sp++)
if (isprint((unsigned char) *sp) || (sp[0] == '\n' && sp[1] == '\0')
|| (sp[0] == '\r' && sp[2] == '\0'))
(void)snprintf(outbuf + strlen(outbuf), 2, "%c", *sp);
else
(void)snprintf(outbuf + strlen(outbuf), 6, "\\x%02x",
0x00ff & (unsigned)*sp);
}
#endif /* !SQUELCH_ENABLE */
void gpsd_vlog(const struct gpsd_errout_t *errout,
const int errlevel,
char *outbuf, size_t outlen,
const char *fmt, va_list ap)
/* assemble msg in vprintf(3) style, use errout hook or syslog for delivery */
{
#ifdef SQUELCH_ENABLE
(void)errout;
(void)errlevel;
(void)fmt;
#else
if (errout->debug >= errlevel) {
char buf[BUFSIZ];
char *err_str;
#if defined(PPS_ENABLE)
gpsd_acquire_reporting_lock();
#endif /* PPS_ENABLE */
switch ( errlevel ) {
case LOG_ERROR:
err_str = "ERROR: ";
break;
case LOG_SHOUT:
err_str = "SHOUT: ";
break;
case LOG_WARN:
err_str = "WARN: ";
break;
case LOG_CLIENT:
err_str = "CLIENT: ";
break;
case LOG_INF:
err_str = "INFO: ";
break;
case LOG_DATA:
err_str = "DATA: ";
break;
case LOG_PROG:
err_str = "PROG: ";
break;
case LOG_IO:
err_str = "IO: ";
break;
case LOG_SPIN:
err_str = "SPIN: ";
break;
case LOG_RAW:
err_str = "RAW: ";
break;
default:
err_str = "UNK: ";
}
assert(errout->label != NULL);
(void)strlcpy(buf, errout->label, sizeof(buf));
(void)strlcat(buf, ":", sizeof(buf));
(void)strlcat(buf, err_str, sizeof(buf));
str_vappendf(buf, sizeof(buf), fmt, ap);
visibilize(outbuf, outlen, buf, strlen(buf));
if (getpid() == getsid(getpid()))
syslog((errlevel <= LOG_SHOUT) ? LOG_ERR : LOG_NOTICE, "%s", outbuf);
else if (errout->report != NULL)
errout->report(outbuf);
else
(void)fputs(outbuf, stderr);
#if defined(PPS_ENABLE)
gpsd_release_reporting_lock();
#endif /* PPS_ENABLE */
}
#endif /* !SQUELCH_ENABLE */
}
void gpsd_log(const struct gpsd_errout_t *errout,
const int errlevel,
const char *fmt, ...)
/* assemble msg in printf(3) style, use errout hook or syslog for delivery */
{
char buf[BUFSIZ];
va_list ap;
buf[0] = '\0';
va_start(ap, fmt);
gpsd_vlog(errout, errlevel, buf, sizeof(buf), fmt, ap);
va_end(ap);
}
const char *gpsd_prettydump(struct gps_device_t *session)
/* dump the current packet in a form optimised for eyeballs */
{
return gpsd_packetdump(session->msgbuf, sizeof(session->msgbuf),
(char *)session->lexer.outbuffer,
session->lexer.outbuflen);
}
/* Define the possible hook strings here so we can get the length */
#define HOOK_ACTIVATE "ACTIVATE"
#define HOOK_DEACTIVATE "DEACTIVATE"
#define HOOK_CMD_MAX (sizeof(DEVICEHOOKPATH) + GPS_PATH_MAX \
+ sizeof(HOOK_DEACTIVATE))
static void gpsd_run_device_hook(struct gpsd_errout_t *errout,
char *device_name, char *hook)
{
struct stat statbuf;
if (stat(DEVICEHOOKPATH, &statbuf) == -1)
gpsd_log(errout, LOG_PROG,
"no %s present, skipped running %s hook\n",
DEVICEHOOKPATH, hook);
else {
int status;
char buf[HOOK_CMD_MAX];
(void)snprintf(buf, sizeof(buf), "%s %s %s",
DEVICEHOOKPATH, device_name, hook);
gpsd_log(errout, LOG_INF, "running %s\n", buf);
status = system(buf);
if (status == -1)
gpsd_log(errout, LOG_ERROR, "error running %s\n", buf);
else
gpsd_log(errout, LOG_INF,
"%s returned %d\n", DEVICEHOOKPATH,
WEXITSTATUS(status));
}
}
int gpsd_switch_driver(struct gps_device_t *session, char *type_name)
{
const struct gps_type_t **dp;
bool first_sync = (session->device_type != NULL);
unsigned int i;
if (first_sync && strcmp(session->device_type->type_name, type_name) == 0)
return 0;
gpsd_log(&session->context->errout, LOG_PROG,
"switch_driver(%s) called...\n", type_name);
for (dp = gpsd_drivers, i = 0; *dp; dp++, i++)
if (strcmp((*dp)->type_name, type_name) == 0) {
gpsd_log(&session->context->errout, LOG_PROG,
"selecting %s driver...\n",
(*dp)->type_name);
gpsd_assert_sync(session);
session->device_type = *dp;
session->driver_index = i;
#ifdef RECONFIGURE_ENABLE
session->gpsdata.dev.mincycle = session->device_type->min_cycle;
#endif /* RECONFIGURE_ENABLE */
/* reconfiguration might be required */
if (first_sync && session->device_type->event_hook != NULL)
session->device_type->event_hook(session,
event_driver_switch);
#ifdef RECONFIGURE_ENABLE
if (STICKY(*dp))
session->last_controller = *dp;
#endif /* RECONFIGURE_ENABLE */
return 1;
}
gpsd_log(&session->context->errout, LOG_ERROR,
"invalid GPS type \"%s\".\n", type_name);
return 0;
}
void gps_context_init(struct gps_context_t *context,
const char *label)
{
(void)memset(context, '\0', sizeof(struct gps_context_t));
//context.readonly = false;
#ifdef TIMEHINT_ENABLE
context->leap_notify = LEAP_NOWARNING;
#endif /* TIMEHINT_ENABLE */
context->serial_write = gpsd_serial_write;
errout_reset(&context->errout);
context->errout.label = (char *)label;
#if defined(PPS_ENABLE)
(void)pthread_mutex_init(&report_mutex, NULL);
#endif /* defined(PPS_ENABLE) */
}
void gpsd_init(struct gps_device_t *session, struct gps_context_t *context,
const char *device)
/* initialize GPS polling */
{
if (device != NULL)
(void)strlcpy(session->gpsdata.dev.path, device,
sizeof(session->gpsdata.dev.path));
session->device_type = NULL; /* start by hunting packets */
#ifdef RECONFIGURE_ENABLE
session->last_controller = NULL;
#endif /* RECONFIGURE_ENABLE */
session->observed = 0;
session->sourcetype = source_unknown; /* gpsd_open() sets this */
session->servicetype = service_unknown; /* gpsd_open() sets this */
session->context = context;
memset( session->subtype, 0, sizeof( session->subtype));
gps_clear_fix(&session->gpsdata.fix);
gps_clear_fix(&session->newdata);
gps_clear_fix(&session->oldfix);
session->gpsdata.set = 0;
gps_clear_dop(&session->gpsdata.dop);
session->gpsdata.epe = NAN;
session->mag_var = NAN;
session->gpsdata.dev.cycle = session->gpsdata.dev.mincycle = 1;
#ifdef TIMING_ENABLE
session->sor = 0.0;
session->chars = 0;
#endif /* TIMING_ENABLE */
/* tty-level initialization */
gpsd_tty_init(session);
/* necessary in case we start reading in the middle of a GPGSV sequence */
gpsd_zero_satellites(&session->gpsdata);
/* initialize things for the packet parser */
packet_reset(&session->lexer);
}
void gpsd_deactivate(struct gps_device_t *session)
/* temporarily release the GPS device */
{
#ifdef RECONFIGURE_ENABLE
if (!session->context->readonly
&& session->device_type != NULL
&& session->device_type->event_hook != NULL) {
session->device_type->event_hook(session, event_deactivate);
}
if (session->device_type != NULL) {
if (session->back_to_nmea
&& session->device_type->mode_switcher != NULL)
session->device_type->mode_switcher(session, 0);
}
#endif /* RECONFIGURE_ENABLE */
gpsd_log(&session->context->errout, LOG_INF,
"closing GPS=%s (%d)\n",
session->gpsdata.dev.path, session->gpsdata.gps_fd);
#if defined(NMEA2000_ENABLE)
if (session->sourcetype == source_can)
(void)nmea2000_close(session);
else
#endif /* of defined(NMEA2000_ENABLE) */
#if defined(PDS_ENABLE)
if (session->sourcetype == source_qrtr)
(void)qmi_pds_close(session);
else
#endif /* of defined(PDS_ENABLE) */
(void)gpsd_close(session);
if (session->mode == O_OPTIMIZE)
gpsd_run_device_hook(&session->context->errout,
session->gpsdata.dev.path,
HOOK_DEACTIVATE);
#ifdef PPS_ENABLE
session->pps_thread.report_hook = NULL; /* tell any PPS-watcher thread to die */
#endif /* PPS_ENABLE */
/* mark it inactivated */
session->gpsdata.online = (timestamp_t)0;
}
#ifdef PPS_ENABLE
static void ppsthread_log(volatile struct pps_thread_t *pps_thread,
int loglevel, const char *fmt, ...)
/* shim function to decouple PPS monitor code from the session structure */
{
struct gps_device_t *device = (struct gps_device_t *)pps_thread->context;
char buf[BUFSIZ];
va_list ap;
switch (loglevel) {
case THREAD_ERROR:
loglevel = LOG_ERROR;
break;
case THREAD_WARN:
loglevel = LOG_WARN;
break;
case THREAD_INF:
loglevel = LOG_INF;
break;
case THREAD_PROG:
loglevel = LOG_PROG;
break;
case THREAD_RAW:
loglevel = LOG_RAW;
break;
}
buf[0] = '\0';
va_start(ap, fmt);
gpsd_vlog(&device->context->errout, loglevel, buf, sizeof(buf), fmt, ap);
va_end(ap);
}
#endif /* PPS_ENABLE */
void gpsd_clear(struct gps_device_t *session)
/* device has been opened - clear its storage for use */
{
session->gpsdata.online = timestamp();
lexer_init(&session->lexer);
session->lexer.errout = session->context->errout;
// session->gpsdata.online = 0;
gps_clear_fix(&session->gpsdata.fix);
session->gpsdata.status = STATUS_NO_FIX;
session->gpsdata.separation = NAN;
session->mag_var = NAN;
session->releasetime = (time_t)0;
session->badcount = 0;
/* clear the private data union */
memset( (void *)&session->driver, '\0', sizeof(session->driver));
#ifdef PPS_ENABLE
/* set up the context structure for the PPS thread monitor */
memset((void *)&session->pps_thread, 0, sizeof(session->pps_thread));
session->pps_thread.devicefd = session->gpsdata.gps_fd;
session->pps_thread.devicename = session->gpsdata.dev.path;
session->pps_thread.log_hook = ppsthread_log;
session->pps_thread.context = (void *)session;
#endif /* PPS_ENABLE */
session->opentime = time(NULL);
}
int gpsd_open(struct gps_device_t *session)
/* open a device for access to its data *
* return: the opened file descriptor
* PLACEHOLDING_FD - for /dev/ppsX
* UNALLOCATED_FD - for open failure
* -1 - for open failure
*/
{
#ifdef NETFEED_ENABLE
/* special case: source may be a URI to a remote GNSS or DGPS service */
if (netgnss_uri_check(session->gpsdata.dev.path)) {
session->gpsdata.gps_fd = netgnss_uri_open(session,
session->gpsdata.dev.path);
session->sourcetype = source_tcp;
gpsd_log(&session->context->errout, LOG_SPIN,
"netgnss_uri_open(%s) returns socket on fd %d\n",
session->gpsdata.dev.path, session->gpsdata.gps_fd);
return session->gpsdata.gps_fd;
/* otherwise, could be an TCP data feed */
} else if (str_starts_with(session->gpsdata.dev.path, "tcp://")) {
char server[strlen(session->gpsdata.dev.path)+1], *port;
socket_t dsock;
(void)strlcpy(server, session->gpsdata.dev.path + 6, sizeof(server));
INVALIDATE_SOCKET(session->gpsdata.gps_fd);
port = strchr(server, ':');
if (port == NULL) {
gpsd_log(&session->context->errout, LOG_ERROR,
"Missing colon in TCP feed spec.\n");
return -1;
}
*port++ = '\0';
gpsd_log(&session->context->errout, LOG_INF,
"opening TCP feed at %s, port %s.\n", server,
port);
if ((dsock = netlib_connectsock(AF_UNSPEC, server, port, "tcp")) < 0) {
gpsd_log(&session->context->errout, LOG_ERROR,
"TCP device open error %s.\n",
netlib_errstr(dsock));
return -1;
} else
gpsd_log(&session->context->errout, LOG_SPIN,
"TCP device opened on fd %d\n", dsock);
session->gpsdata.gps_fd = dsock;
session->sourcetype = source_tcp;
return session->gpsdata.gps_fd;
/* or could be UDP */
} else if (str_starts_with(session->gpsdata.dev.path, "udp://")) {
char server[strlen(session->gpsdata.dev.path)+1], *port;
socket_t dsock;
(void)strlcpy(server, session->gpsdata.dev.path + 6, sizeof(server));
INVALIDATE_SOCKET(session->gpsdata.gps_fd);
port = strchr(server, ':');
if (port == NULL) {
gpsd_log(&session->context->errout, LOG_ERROR,
"Missing colon in UDP feed spec.\n");
return -1;
}
*port++ = '\0';
gpsd_log(&session->context->errout, LOG_INF,
"opening UDP feed at %s, port %s.\n", server,
port);
if ((dsock = netlib_connectsock(AF_UNSPEC, server, port, "udp")) < 0) {
gpsd_log(&session->context->errout, LOG_ERROR,
"UDP device open error %s.\n",
netlib_errstr(dsock));
return -1;
} else
gpsd_log(&session->context->errout, LOG_SPIN,
"UDP device opened on fd %d\n", dsock);
session->gpsdata.gps_fd = dsock;
session->sourcetype = source_udp;
return session->gpsdata.gps_fd;
}
#endif /* NETFEED_ENABLE */
#ifdef PASSTHROUGH_ENABLE
if (str_starts_with(session->gpsdata.dev.path, "gpsd://")) {
char server[strlen(session->gpsdata.dev.path)+1], *port;
socket_t dsock;
(void)strlcpy(server, session->gpsdata.dev.path + 7, sizeof(server));
INVALIDATE_SOCKET(session->gpsdata.gps_fd);
if ((port = strchr(server, ':')) == NULL) {
port = DEFAULT_GPSD_PORT;
} else
*port++ = '\0';
gpsd_log(&session->context->errout, LOG_INF,
"opening remote gpsd feed at %s, port %s.\n",
server, port);
if ((dsock = netlib_connectsock(AF_UNSPEC, server, port, "tcp")) < 0) {
gpsd_log(&session->context->errout, LOG_ERROR,
"remote gpsd device open error %s.\n",
netlib_errstr(dsock));
return -1;
} else
gpsd_log(&session->context->errout, LOG_SPIN,
"remote gpsd feed opened on fd %d\n", dsock);
/* watch to remote is issued when WATCH is */
session->gpsdata.gps_fd = dsock;
session->sourcetype = source_gpsd;
return session->gpsdata.gps_fd;
}
#endif /* PASSTHROUGH_ENABLE */
#if defined(NMEA2000_ENABLE)
if (str_starts_with(session->gpsdata.dev.path, "nmea2000://")) {
return nmea2000_open(session);
}
#endif /* defined(NMEA2000_ENABLE) */
#if defined(PDS_ENABLE)
if (str_starts_with(session->gpsdata.dev.path, "pds://")) {
return qmi_pds_open(session);
}
#endif /* defined(PDS_ENABLE) */
/* fall through to plain serial open */
/* could be a naked /dev/ppsX */
return gpsd_serial_open(session);
}
int gpsd_activate(struct gps_device_t *session, const int mode)
/* acquire a connection to the GPS device */
{
if (mode == O_OPTIMIZE)
gpsd_run_device_hook(&session->context->errout,
session->gpsdata.dev.path, HOOK_ACTIVATE);
session->gpsdata.gps_fd = gpsd_open(session);
if (mode != O_CONTINUE)
session->mode = mode;
// cppcheck-suppress pointerLessThanZero
if (session->gpsdata.gps_fd < 0) {
/* return could be -1, PLACEHOLDING_FD, of UNALLOCATED_FD */
if ( PLACEHOLDING_FD == session->gpsdata.gps_fd ) {
/* it is /dev/ppsX, need to set devicename, etc. */
gpsd_clear(session);
}
return session->gpsdata.gps_fd;
}
#ifdef NON_NMEA0183_ENABLE
/* if it's a sensor, it must be probed */
if ((session->servicetype == service_sensor) &&
(session->sourcetype != source_can && session->sourcetype != source_qrtr)) {
const struct gps_type_t **dp;
for (dp = gpsd_drivers; *dp; dp++) {
if ((*dp)->probe_detect != NULL) {
gpsd_log(&session->context->errout, LOG_PROG,
"Probing \"%s\" driver...\n",
(*dp)->type_name);
/* toss stale data */
(void)tcflush(session->gpsdata.gps_fd, TCIOFLUSH);
if ((*dp)->probe_detect(session) != 0) {
gpsd_log(&session->context->errout, LOG_PROG,
"Probe found \"%s\" driver...\n",
(*dp)->type_name);
session->device_type = *dp;
gpsd_assert_sync(session);
goto foundit;
} else
gpsd_log(&session->context->errout, LOG_PROG,
"Probe not found \"%s\" driver...\n",
(*dp)->type_name);
}
}
gpsd_log(&session->context->errout, LOG_PROG,
"no probe matched...\n");
}
foundit:
#endif /* NON_NMEA0183_ENABLE */
gpsd_clear(session);
gpsd_log(&session->context->errout, LOG_INF,
"gpsd_activate(%d): activated GPS (fd %d)\n",
session->mode, session->gpsdata.gps_fd);
/*
* We might know the device's type, but we shouldn't assume it has
* retained its settings. A revert hook might well have undone
* them on the previous close. Fire a reactivate event so drivers
* can do something about this if they choose.
*/
if (session->device_type != NULL
&& session->device_type->event_hook != NULL)
session->device_type->event_hook(session, event_reactivate);
return session->gpsdata.gps_fd;
}
#ifndef NOFLOATS_ENABLE
/*****************************************************************************
Carl Carter of SiRF supplied this algorithm for computing DOPs from
a list of visible satellites (some typos corrected)...
For satellite n, let az(n) = azimuth angle from North and el(n) be elevation.
Let:
a(k, 1) = sin az(k) * cos el(k)
a(k, 2) = cos az(k) * cos el(k)
a(k, 3) = sin el(k)
Then form the line-of-sight matrix A for satellites used in the solution:
| a(1,1) a(1,2) a(1,3) 1 |
| a(2,1) a(2,2) a(2,3) 1 |
| : : : : |
| a(n,1) a(n,2) a(n,3) 1 |
And its transpose A~:
|a(1, 1) a(2, 1) . . . a(n, 1) |
|a(1, 2) a(2, 2) . . . a(n, 2) |
|a(1, 3) a(2, 3) . . . a(n, 3) |
| 1 1 . . . 1 |
Compute the covariance matrix (A~*A)^-1, which is guaranteed symmetric:
| s(x)^2 s(x)*s(y) s(x)*s(z) s(x)*s(t) |
| s(y)*s(x) s(y)^2 s(y)*s(z) s(y)*s(t) |
| s(z)*s(x) s(z)*s(y) s(z)^2 s(z)*s(t) |
| s(t)*s(x) s(t)*s(y) s(t)*s(z) s(t)^2 |
Then:
GDOP = sqrt(s(x)^2 + s(y)^2 + s(z)^2 + s(t)^2)
TDOP = sqrt(s(t)^2)
PDOP = sqrt(s(x)^2 + s(y)^2 + s(z)^2)
HDOP = sqrt(s(x)^2 + s(y)^2)
VDOP = sqrt(s(z)^2)
Here's how we implement it...
First, each compute element P(i,j) of the 4x4 product A~*A.
If S(k=1,k=n): f(...) is the sum of f(...) as k varies from 1 to n, then
applying the definition of matrix product tells us:
P(i,j) = S(k=1,k=n): B(i, k) * A(k, j)
But because B is the transpose of A, this reduces to
P(i,j) = S(k=1,k=n): A(k, i) * A(k, j)
This is not, however, the entire algorithm that SiRF uses. Carl writes:
> As you note, with rounding accounted for, most values agree exactly, and
> those that don't agree our number is higher. That is because we
> deweight some satellites and account for that in the DOP calculation.
> If a satellite is not used in a solution at the same weight as others,
> it should not contribute to DOP calculation at the same weight. So our
> internal algorithm does a compensation for that which you would have no
> way to duplicate on the outside since we don't output the weighting
> factors. In fact those are not even available to API users.
Queried about the deweighting, Carl says:
> In the SiRF tracking engine, each satellite track is assigned a quality
> value based on the tracker's estimate of that signal. It includes C/No
> estimate, ability to hold onto the phase, stability of the I vs. Q phase
> angle, etc. The navigation algorithm then ranks all the tracks into
> quality order and selects which ones to use in the solution and what
> weight to give those used in the solution. The process is actually a
> bit of a "trial and error" method -- we initially use all available
> tracks in the solution, then we sequentially remove the lowest quality
> ones until the solution stabilizes. The weighting is inherent in the
> Kalman filter algorithm. Once the solution is stable, the DOP is
> computed from those SVs used, and there is an algorithm that looks at
> the quality ratings and determines if we need to deweight any.
> Likewise, if we use altitude hold mode for a 3-SV solution, we deweight
> the phantom satellite at the center of the Earth.
So we cannot exactly duplicate what SiRF does internally. We'll leave
HDOP alone and use our computed values for VDOP and PDOP. Note, this
may have to change in the future if this code is used by a non-SiRF
driver.
******************************************************************************/
static gps_mask_t fill_dop(const struct gpsd_errout_t *errout,
const struct gps_data_t * gpsdata,
struct dop_t * dop)
{
double prod[4][4];
double inv[4][4];
double satpos[MAXCHANNELS][4];
double xdop, ydop, hdop, vdop, pdop, tdop, gdop;
int i, j, k, n;
memset(satpos, 0, sizeof(satpos));
for (n = k = 0; k < gpsdata->satellites_visible; k++) {
if (gpsdata->skyview[k].used && !SBAS_PRN(gpsdata->skyview[k].PRN))
{
const struct satellite_t *sp = &gpsdata->skyview[k];
satpos[n][0] = sin(sp->azimuth * DEG_2_RAD)
* cos(sp->elevation * DEG_2_RAD);
satpos[n][1] = cos(sp->azimuth * DEG_2_RAD)
* cos(sp->elevation * DEG_2_RAD);
satpos[n][2] = sin(sp->elevation * DEG_2_RAD);
satpos[n][3] = 1;
gpsd_log(errout, LOG_INF, "PRN=%3d az=%3d el=%2d (%f, %f, %f)\n",
gpsdata->skyview[k].PRN,
gpsdata->skyview[k].azimuth,
gpsdata->skyview[k].elevation,
satpos[n][0], satpos[n][1], satpos[n][2]);
n++;
}
}
/* can't use gpsdata->satellites_used as that is a counter for xxGSA,
* and gets cleared at odd times */
gpsd_log(errout, LOG_INF, "Sats used (%d):\n", n);
/* If we don't have 4 satellites then we don't have enough information to calculate DOPS */
if (n < 4) {
#ifdef __UNUSED__
gpsd_log(errout, LOG_DATA + 2,
"Not enough satellites available %d < 4:\n",
n);
#endif /* __UNUSED__ */
return 0; /* Is this correct return code here? or should it be ERROR_SET */
}
memset(prod, 0, sizeof(prod));
memset(inv, 0, sizeof(inv));
#ifdef __UNUSED__
gpsd_log(errout, LOG_INF, "Line-of-sight matrix:\n");
for (k = 0; k < n; k++) {
gpsd_log(errout, LOG_INF, "%f %f %f %f\n",
satpos[k][0], satpos[k][1], satpos[k][2], satpos[k][3]);
}
#endif /* __UNUSED__ */
for (i = 0; i < 4; ++i) { //< rows
for (j = 0; j < 4; ++j) { //< cols
prod[i][j] = 0.0;
for (k = 0; k < n; ++k) {
prod[i][j] += satpos[k][i] * satpos[k][j];
}
}
}
#ifdef __UNUSED__
gpsd_log(errout, LOG_INF, "product:\n");
for (k = 0; k < 4; k++) {
gpsd_log(errout, LOG_INF, "%f %f %f %f\n",
prod[k][0], prod[k][1], prod[k][2], prod[k][3]);
}
#endif /* __UNUSED__ */
if (matrix_invert(prod, inv)) {
#ifdef __UNUSED__
/*
* Note: this will print garbage unless all the subdeterminants
* are computed in the invert() function.
*/
gpsd_log(errout, LOG_RAW, "inverse:\n");
for (k = 0; k < 4; k++) {
gpsd_log(errout, LOG_RAW,
"%f %f %f %f\n",
inv[k][0], inv[k][1], inv[k][2], inv[k][3]);
}
#endif /* __UNUSED__ */
} else {
#ifndef USE_QT
gpsd_log(errout, LOG_DATA,
"LOS matrix is singular, can't calculate DOPs - source '%s'\n",
gpsdata->dev.path);
#endif
return 0;
}
xdop = sqrt(inv[0][0]);
ydop = sqrt(inv[1][1]);
hdop = sqrt(inv[0][0] + inv[1][1]);
vdop = sqrt(inv[2][2]);
pdop = sqrt(inv[0][0] + inv[1][1] + inv[2][2]);
tdop = sqrt(inv[3][3]);
gdop = sqrt(inv[0][0] + inv[1][1] + inv[2][2] + inv[3][3]);
#ifndef USE_QT
gpsd_log(errout, LOG_DATA,
"DOPS computed/reported: X=%f/%f, Y=%f/%f, H=%f/%f, V=%f/%f, "
"P=%f/%f, T=%f/%f, G=%f/%f\n",
xdop, dop->xdop, ydop, dop->ydop, hdop, dop->hdop, vdop,
dop->vdop, pdop, dop->pdop, tdop, dop->tdop, gdop, dop->gdop);
#endif
if (isnan(dop->xdop) != 0) {
dop->xdop = xdop;
}
if (isnan(dop->ydop) != 0) {
dop->ydop = ydop;
}
if (isnan(dop->hdop) != 0) {
dop->hdop = hdop;
}
if (isnan(dop->vdop) != 0) {
dop->vdop = vdop;
}
if (isnan(dop->pdop) != 0) {
dop->pdop = pdop;
}
if (isnan(dop->tdop) != 0) {
dop->tdop = tdop;
}
if (isnan(dop->gdop) != 0) {
dop->gdop = gdop;
}
return DOP_SET;
}
static void gpsd_error_model(struct gps_device_t *session,
struct gps_fix_t *fix, struct gps_fix_t *oldfix)
/* compute errors and derived quantities */
{
/*
* Now we compute derived quantities. This is where the tricky error-
* modeling stuff goes. Presently we don't know how to derive
* time error.
*
* Some drivers set the position-error fields. Only the Zodiacs
* report speed error. Nobody reports track error or climb error.
*
* The UERE constants are our assumption about the base error of
* GPS fixes in different directions.
*/
#define H_UERE_NO_DGPS 15.0 /* meters, 95% confidence */
#define H_UERE_WITH_DGPS 3.75 /* meters, 95% confidence */
#define V_UERE_NO_DGPS 23.0 /* meters, 95% confidence */
#define V_UERE_WITH_DGPS 5.75 /* meters, 95% confidence */
#define P_UERE_NO_DGPS 19.0 /* meters, 95% confidence */
#define P_UERE_WITH_DGPS 4.75 /* meters, 95% confidence */
double h_uere, v_uere, p_uere;
if (NULL == session)
return;
h_uere =
(session->gpsdata.status ==
STATUS_DGPS_FIX ? H_UERE_WITH_DGPS : H_UERE_NO_DGPS);
v_uere =
(session->gpsdata.status ==
STATUS_DGPS_FIX ? V_UERE_WITH_DGPS : V_UERE_NO_DGPS);
p_uere =
(session->gpsdata.status ==
STATUS_DGPS_FIX ? P_UERE_WITH_DGPS : P_UERE_NO_DGPS);
/* sanity check the speed, 10,000 m/s should be a nice max */
if ( 9999.9 < fix->speed )
fix->speed = NAN;
else if ( -9999.9 > fix->speed )
fix->speed = NAN;
/* sanity check the climb, 10,000 m/s should be a nice max */
if ( 9999.9 < fix->climb )
fix->climb = NAN;
else if ( -9999.9 > fix->climb )
fix->climb = NAN;
/*
* OK, this is not an error computation, but we're at the right
* place in the architecture for it. Compute speed over ground
* and climb/sink in the simplest possible way.
*/
if (fix->mode >= MODE_2D && oldfix->mode >= MODE_2D
&& isnan(fix->speed) != 0) {
if (fix->time == oldfix->time)
fix->speed = 0;
else
fix->speed =
earth_distance(fix->latitude, fix->longitude,
oldfix->latitude, oldfix->longitude)
/ (fix->time - oldfix->time);
}
if (fix->mode >= MODE_3D && oldfix->mode >= MODE_3D
&& isnan(fix->climb) != 0) {
if (fix->time == oldfix->time)
fix->climb = 0;
else if (isnan(fix->altitude) == 0 && isnan(oldfix->altitude) == 0) {
fix->climb =
(fix->altitude - oldfix->altitude) / (fix->time -
oldfix->time);
}
}
/*
* Field reports match the theoretical prediction that
* expected time error should be half the resolution of
* the GPS clock, so we put the bound of the error
* in as a constant pending getting it from each driver.
*
* In an ideal world, we'd increase this if no leap-second has
* been seen and it's less than 750s (one almanac load cycle) from
* device powerup. Alas, we have no way to know when device
* powerup occurred - depending on the receiver design it could be
* when the hardware was first powered up or when it was first
* opened. Also, some devices (notably plain NMEA0183 receivers)
* never ship an indication of when they have valid leap second.
*/
if (isnan(fix->time) == 0 && isnan(fix->ept) != 0)
fix->ept = 0.005;
/* Other error computations depend on having a valid fix */
if (fix->mode >= MODE_2D) {
if (isnan(fix->epx) != 0 && isfinite(session->gpsdata.dop.hdop) != 0)
fix->epx = session->gpsdata.dop.xdop * h_uere;
if (isnan(fix->epy) != 0 && isfinite(session->gpsdata.dop.hdop) != 0)
fix->epy = session->gpsdata.dop.ydop * h_uere;
if ((fix->mode >= MODE_3D)
&& isnan(fix->epv) != 0 && isfinite(session->gpsdata.dop.vdop) != 0)
fix->epv = session->gpsdata.dop.vdop * v_uere;
if (isnan(session->gpsdata.epe) != 0
&& isfinite(session->gpsdata.dop.pdop) != 0)
session->gpsdata.epe = session->gpsdata.dop.pdop * p_uere;
else
session->gpsdata.epe = NAN;
/*
* If we have a current fix and an old fix, and the packet handler
* didn't set the speed error and climb error members itself,
* try to compute them now.
*/
if (isnan(fix->eps) != 0) {
if (oldfix->mode > MODE_NO_FIX && fix->mode > MODE_NO_FIX
&& isnan(oldfix->epx) == 0 && isnan(oldfix->epy) == 0
&& isnan(oldfix->time) == 0 && isnan(fix->time) == 0
&& fix->time > oldfix->time) {
timestamp_t t = fix->time - oldfix->time;
double e =
EMIX(oldfix->epx, oldfix->epy) + EMIX(fix->epx, fix->epy);
fix->eps = e / t;
} else
fix->eps = NAN;
}
if ((fix->mode >= MODE_3D)
&& isnan(fix->epc) != 0 && fix->time > oldfix->time) {
if (oldfix->mode >= MODE_3D && fix->mode >= MODE_3D) {
timestamp_t t = fix->time - oldfix->time;
double e = oldfix->epv + fix->epv;
/* if vertical uncertainties are zero this will be too */
fix->epc = e / t;
}
/*
* We compute a track error estimate solely from the
* position of this fix and the last one. The maximum
* track error, as seen from the position of last fix, is
* the angle subtended by the two most extreme possible