GCS_MAVLink: added ALTITUDE message #141

[peterbarker]

[peterbarker]

I brought this up for discussion at the DevCall. I've also fixed the compilation so we can see what it costs.

A few things came up. The first is that @hendjoshsr71 pointed out this isn't really a good "all in one altitude message". It doesn't include any information about qnh altitudes, perhaps the most important thing up-and-coming.

tridge suggested we could add a "is_for_current_location" boolean to the TERRAIN_REPORT message - Randy amended that to "a flags field", but the intent is the same. Reuse the existing TERRAIN_REPORT message but include additional information sufficient for the GCS to know this is the current altitude above terrain. I did note we'd need to take the whole extension-field-zero semantics into account when creating the flags field.

No determination was come to - I ran out of time to progress this on the call, but at least we have more talking points.

[peterbarker]

Durandal:

 Binary Name      Text [B]        Data [B]     BSS (B)        Total Flash Change [B] (%)      Flash Free After PR (B)
---------------  --------------  -----------  -------------  ----------------------------  -------------------------
blimp            504 (+0.0389%)  0 (0.0000%)  0 (0.0000%)    504 (+0.0388%)                                   668232
ardusub          524 (+0.0335%)  0 (0.0000%)  4 (+0.0015%)   524 (+0.0334%)                                   398952
ardurover        520 (+0.0323%)  0 (0.0000%)  0 (0.0000%)    520 (+0.0322%)                                   351116
antennatracker   524 (+0.0387%)  0 (0.0000%)  -4 (-0.0015%)  524 (+0.0387%)                                   610324
arduplane        524 (+0.0298%)  0 (0.0000%)  -4 (-0.0015%)  524 (+0.0297%)                                   201396
arducopter-heli  524 (+0.0293%)  0 (0.0000%)  4 (+0.0015%)   524 (+0.0293%)                                   175732
arducopter       524 (+0.0294%)  0 (0.0000%)  4 (+0.0015%)   524 (+0.0294%)                                   182764