Depth widget ideas (simple to fancy)

[ES-Alexander]

Transferring from our internal discussion 3 months ago / the initial PR:

• extents should show the surface and an optional water column depth
  • if no altitude sensor either allow setting a "known bottom distance" variable, or just have no explicit bottom shown
• local crop -> show zoomed in local area
  • dots (bubbles?) above and below to show that some distance is "missing"
  • number of dots gives a sense of relative distance (e.g. if close-ish to the bottom but far from the top, maybe have 4 dots at the top and 1 at the bottom)
  • zero dots when an extent is within the 'zoom' region
• trail should fade in from left to right, with configurable widget width and shown duration
  • time scale should be linear by default (-> constant velocity shows a straight line)
  • may be worth providing a logarithmic timescale option, to allow compressing more samples history into the available space
  • altitude sensor readings should also be trailed, if they're available
• display of current position and altitude would be cute to show as an ROV (with tether trail) and an anchor
  • ideally (long term?) the vehicle icon would be configurable, so people can put their own design instead
• maybe show the surface as wavy water 〰️ 🌊
• could show vehicle pitch (per #1053)

[ES-Alexander]

• It would be nice to also be able to show the current depth or terrain-altitude target, depending on the flight mode
  • idea from @clydemcqueen in this forum comment

[ES-Alexander]

• this could also be adapted to show similar concepts for aerial vehicles (e.g. to resolve #177)
  • we could have a separate widget for this, but the functionality would be nearly identical, so I think it's better to just make it flexible enough to work for both (which could then be epic in future if someone makes a submersible sea-plane or something :-P)
  • in the air it would be nice to have the trail look like air trails instead of a tether, but that could likely be achieved by just making the colour configurable (although we may want to allow separate colours for above/below the surface)
    • in a similar vein, we could potentially change the anchor to a ladder or something when above ground, although it may be fine to leave as is
• aerial vehicles often have terrain maps, and hopefully water-based ones will in future as well, so we should also allow displaying the expected terrain height compared with the measured one

[rafaellehmkuhl]

• we could have a separate widget for this, but the functionality would be nearly identical, so I think it's better to just make it flexible enough to work for both (which could then be epic in future if someone makes a submersible sea-plane or something :-P)

As you said, the functionality is very similar, so I agree we should have one widget with both functionalities, at least at a first glance.

Maybe we can test by having them completely separated for a while, watch the evolution of both, and if we see they can indeed be merged, we do it.