path: root/TODO

This is the gpsd to-do list.  If you're viewing it with Emacs, try
doing Ctl-C Ctl-t and browsing through the outline headers.  Ctl-C Ctl-a 
will unfold them again.

** Bugs in gpsd and its clients:

*** There's a report that RoyalTek support broke between 2.25 and 2.28 

There's a report that RoyalTek support broke between 2.25 and 2.28 by
David Mandala <davidm@them.com>.  His workaround is to condition out
SiRF-II support; it works OK in NMEA mode.  The Royaltek died in an
accident, so we're stuck until someone else can test this.

*** Axiom Sandpiper II OEM NMEA GPS Module gets mistaken for an FV-18

David Mandala <davidm@them.com> reported this bug.  He says it can 
be worked around by setting the port to 4800 manually before starting
GPSD.  David sent ESR one of these, it's somewhere in his piles of
stuff, testing will get done when it surfaces.  More on the Sandpiper
at <http://www.allsurplus.net/Axiom/>.

*** Garmin binary support failed on x86_64

Member sizes in the packed binary structure Packet_t were wrong.
Gary Miller has attempted to fix this, but it has not yet been tested
on a 64-bit machine.

*** True North support confuses track with heading

Robin Darroch has pointed out that the support for the True North
compass device confuses track (course over ground) with heading.
This should probably be fixed.  However, the TNT code was sent 
to us by a TNT user involved in the 2004 DARPA Grand Challenge 
and therefore presumably meets actual production needs.  For
this reason, and because separating track froom heading would 
ripple through several places including gps.h and the client
implementations, we're not going to try to fix this until we
have a TNT device (or something else that makes the same
distinction) to test with.

** Bugs exposed by gpsd in other software

*** Multiple definitions of symbol _gpsd_report

Some people building gpsd get 'multiple definitions of symbol _gpsd_report'
as a warning.  This seems to be a result of two bugs in libtool, one
of which masks the other on i386. gpsd_report() is indeed multiply
defined, the problem is that libtool generates libgps.o where it 
should generate -lgps and *all* instances (rather than just the first
to be incorporated by other linkage demands) are linked in.

*** The 2.3.0-beta version of OpenMotif shipped with Fedora Care 5 is buggy

xgps appears to tickle a bug (described at http://bugs.motifzone.net/ as
bugs 1330 and 1331) in OpenMotif.  This bug has been marked FIXED, so
the next release of OpenMotif will probably fix it.  Until then, we
suggest you drop back to an OpenMotif stable version like 2.2.2.

** To do:

*** Stop using a compiled-in UTC-TAI offset

Instead, from the hotplug script, maintain a local offset file:

1. If there is no local offset file, download the current leap-second
offset from <http://hpiers.obspm.fr/iers/bul/bulc/> or
<ftp://maia.usno.navy.mil/ser7/tai-utc.dat> and copy it to a
local offset file

2. If there is a local offset file, consider it stale after five
months and reload it.

3. gpsd should read the local offset file when it starts up, if
it exists.

*** SiRF firmware uploader

Chris Kuethe has shipped a 0.0 alpha version.  It is not yet 
resolved whether SiRF Technology will allow us to ship the 
binary loader code needed to actually use it.

*** RINEX-format dumping of raw satellite data

It would be useful to be able to extract RINEX-format data from any
GPS device that can report pseudoranges etc.  This belongs in the
daemon because the device drivers are already doing the
packet-cracking needed to get the data off the chips.

*** RTCM support.

We have an RTCM packet decoder, and untested scratch code to serve
RTCM packets to port 2101.  Here's the plan for the rest of it:

1) Inversion needs to be done somewhere in the encoding logic.

2) Wolfgang's decoder-hardening patches.

3) Test productions.  I have one that tests dumping and one that uses   
   passthrough mode to test that pack() and repack() are inverse.  We
   should have an undumping torture test.

4) What about rtcm_output_mag() anyway?  Should that be made
   available as an output mode of rtcmdecode and documented?

5) Python libraries must grok RTCM dump format.

6) Extend the test framework so we can verify RTCM service.

7) Get rid of the -d option by hacking open_device() so that when it
   sees a command-line option of the form server:port (with no
   embedded backslashes) it opens a socket to read from that server.
   Now any GPS-packet and RTCM data sources given on the command line
   can be remote as well as local.

8) Generate and broadcast RTCM corrections from an attached device?
   Might not be possible -- appears to need nanosecond timing.

*** Do the research to figure out just what is going on with status bits

NMEA actually has *four* kinds of validity bits: Mode, Status, the
Active/Void bit (some sources interpret 'V' as 'Navigation receiver
warning'), and in later versions the FAA indicator mode.  Sentences
that have an Active/Void send V when there is no fix, so the position
data is no good.

Let's look at which sentences send what:

                GPRMC     GPGLL     GPGGA     GPGSA
Returns fix      Yes       Yes       Yes        No
Returns status   No        Yes       Yes        No
Returns mode     No        No        No         Yes
Returns A/V      Yes       Yes       No         No

In addition, some sentences use empty fields to signify invalid data.

My first conclusion from looking at this table is that the designers
of NMEA 0183 should be hung for galloping incompetence.  But never mind that.
What are we to make of this mess?

The fact that the FV18 sends GPRMC/GPGLL/GPGGA but not GPGSA
argues that GPGSA is optional.  I don't see how it can be, since it
seems to be the only status bit that applies to altitude.  Just how are
we supposed to know when altitude is valid if it doesn't ship GSA?  
Can a receiver ever ship a non-empty but invalid altitude?

Which of these override which other bits?  I don't think status is ever
nonzero when mode is zero. So status overrides mode.  What other such
relationships are there?

News flash: it develops that the "Navigation receiver warning" is
supposed to indicate a valid fix that has a DOP too high or fails
an elevation test.

** Future features (?)

*** Audio cues in the client when the fix status changes

Calum writes:
>Is it possible to add functionality ( with a switch to enable it to
>avoid annoying those that don't want it) so that beeps indicate NO
>FIX, FIX, and OFFLINE status changes?
>
>For example - I run cgps and my laptop battery doesn't always supply
>my PS2 port-powered GPS device with enough power, and it goes into
>OFFLINE mode. As I can't drive, and check my laptop all the time, if
>it emitted 5 1 second beeps when it went OFFLINE, it would be a handy alert.
>
>Similarly, a PCMCIA "eject" 2 beeps for NO FIX, and a PCMCIA "happy" 2
>beeps when it gets a fix again?
>
>Or something like that.

This is a good idea for supporting hands-free operation, e.g. while driving.

It would be an easy first project for somebody who wants to get into
the client code.

*** Subsecond polling

gpsd relies on the GPS to periodically send PVT reports to it.

Most GPSes send PVT reports once a second.  No NMEA GPS I've ever seen
allows you to set a cycle time of less than a second.  This is because
at 4800bps, a full PVT report takes just under one second in NMEA.

At 50km/h (31mi/h) that's 13.8 meters change in position between
updates, about the same as the uncertainty of position under typical
conditions.

There is, however, a way to sample GPSes at higher frequency.  SiRF
chips, and some others, allow you to shut down periodic notifications
and poll them for PVT.  At 57600bps we could poll a NMEA GPS 16 times
a second, and a SiRF one maybe 18 times a second.

Is this worth doing?  Maybe.  It would reduce fix latency, possibly
to good effect if your GPS is in motion.  Opinions?  Calculations?

Gary Miller reports that the Garmin GPS 18 LVC-5m and the GPS 18-5Hz
both report 5 times a second, but he doesn't have either to test.

Alas, Chris Kuethe reports:
>At least on the SiRF 2 and 3 receivers I have, you get one fix per
>second. I cooked up a test harness to disable as many periodic
>messages as possible and then poll as quickly as possible, and the
>receiver would not kick out more than one fix per second. Foo!

*** Set the system time zone from latitude/longitude

If we're going to give gpsd the capability to set system time via
ntpd, why not let it set timezone as well?  A good thing for hackers
travelling with laptops!

The major issue here is that I have not yet found code, or a
database, that would allow mapping from lon/lat to timezone.
And the rules change from year to year.

Actually this should be built as a specialized client, as some
people won't want it.

From <http://www.linuxsa.org.au/tips/time.html>:

    The timezone under Linux is set by a symbolic link from
    /etc/localtime[1] to a file in the /usr/share/zoneinfo[2] directory
    that corresponds with what timezone you are in. For example, since I'm
    in South Australia, /etc/localtime is a symlink to
    /usr/share/zoneinfo/Australia/South. To set this link, type:

    ln -sf ../usr/share/zoneinfo/your/zone /etc/localtime

    Replace your/zone with something like Australia/NSW or
    Australia/Perth. Have a look in the directories under
    /usr/share/zoneinfo to see what timezones are available.

    [1] This assumes that /usr/share/zoneinfo is linked to /etc/localtime as it is under Red Hat Linux.

    [2] On older systems, you'll find that /usr/lib/zoneinfo is used
    instead of /usr/share/zoneinfo.

Changing the hardlink will, of course, update the system timezone for
all users.  If I were designing this feature, I'd ensure that the
system timezone can be overridden by a user-set TZ, but I don't know
if it actually works that way.

If I'm reading the tea leaves correctly, this functionality is actually
embedded in the GCC library version of tzset(), so the same method will
work on any system that uses that.

Problem: system daemons use the timezone set when they start up. You
can't get them to grok a new one short of rebooting.

Sources: 

Sources for Time Zone and Daylight Saving Time Data
http://www.twinsun.com/tz/tz-link.htm

Free time-zone maps of the U.S.
http://www.manifold.net/download/freemaps.html

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