[Bug 791601] new element: gpsdsrc

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=791601

--- Comment #4 from Nicolas Dufresne (stormer) <nicolas at ndufresne.ca> ---
(In reply to Tim-Philipp Müller from comment #3)
> What is the actual / eventual purpose of this element, if I may ask?

Real-Time stream geolocalisation seems very useful to me. Combine this with
color video, depth stream and gyroscopic data, you could turn a video recording
into 3D.

> 
> It sounds rather niche to me.
> 
> What is the data format being output?

Currently it is gps_fix_t from gpsd library.

> 
> What would seem more generally useful to me is for example an element that
> puts current GPS co-ordinates as metadata on buffers, for example.

Though that needs to happen in two steps, since you need to first synch the GPS
fixes with the data because of the delays. You cannot request a fix in the
past, you need to capture, synch and then you can merge or mux.

> 
> OOC, what's the dbus service used by e.g. GNOME to get current geo
> co-ordinates?

Gypsy, but it's a totally different multiplexer. It does not matter really, one
can add a source for that.

The format:

typedef double timestamp_t;    /* Unix time in seconds with fractional part */

struct gps_fix_t {
    timestamp_t time;    /* Time of update */
    int    mode;    /* Mode of fix */
#define MODE_NOT_SEEN    0    /* mode update not seen yet */
#define MODE_NO_FIX    1    /* none */
#define MODE_2D      2    /* good for latitude/longitude */
#define MODE_3D      3    /* good for altitude/climb too */
    double ept;        /* Expected time uncertainty */
    double latitude;    /* Latitude in degrees (valid if mode >= 2) */
    double epy;      /* Latitude position uncertainty, meters */
    double longitude;    /* Longitude in degrees (valid if mode >= 2) */
    double epx;      /* Longitude position uncertainty, meters */
    double altitude;    /* Altitude in meters (valid if mode == 3) */
    double epv;      /* Vertical position uncertainty, meters */
    double track;    /* Course made good (relative to true north) */
    double epd;        /* Track uncertainty, degrees */
    double speed;    /* Speed over ground, meters/sec */
    double eps;        /* Speed uncertainty, meters/sec */
    double climb;       /* Vertical speed, meters/sec */
    double epc;        /* Vertical speed uncertainty */
};

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