Bug 64762

The climb rate algorithm in gypsy_client_set_position looks bogus to me.

Consider a GPS that outputs a new altitude every second (which is typical), and outputs the following sequences of altitudes:
0 1 1 1 1 1 1 1 1 1 1 0      

The climb rate algorithm will compute the following:
0 1 1 1 1 1 1 1 1 1 1 -0.1

(Of course the consecutive 1's are not actually computed, but just not updated).

I would expect if I integrate the climb rate values, that I would roughly track the altitude values.

WIth the current algorithm this is grossly violated (with the above sequence we arrive at 9.9, instead of ~0).

This is the code in question:
        if (fields_set & POSITION_ALTITUDE) {
                if (priv->position_fields & POSITION_ALTITUDE) {
                        if (priv->altitude != altitude) {
                                /* If we've got a timestamp for the last alt
                                   then we are able to calculate the climb. */
                                if (priv->last_alt_timestamp > 0) {
                                        int dt;
                                        double da, climb;

                                        dt = priv->timestamp - priv->last_alt_timestamp;
                                        da = altitude - priv->altitude;
                                        climb = da / (double) dt;
                                        gypsy_client_set_course (client,
                                                                 COURSE_CLIMB,
                                                                 0.0, 0.0, 
                                                                 climb);
                                }

                                priv->altitude = altitude;
                                priv->last_alt_timestamp = priv->timestamp;
                                changed = TRUE;
                        } 
                } else {
                        priv->altitude = altitude;
                        priv->last_alt_timestamp = priv->timestamp;
                        priv->position_fields |= POSITION_ALTITUDE;
                        changed = TRUE;
                }
        }

Furthermore, it's a bit unfortunate that the Gypsy API does only support integer second timestamps; GPS with a higher update rate than 1Hz are getting common (Garmin GLO, most newer u-blox chips/modules).