Estimated bottom depth always n/a

[sqshemet]

Describe the bug
I don't think I've ever seen a value shown for "Est. bottom depth", on any of the screens? I assume this is supposed to display when a mission has waypoints? If it's not applicable for a waypoint mission, when is it applicable?

To Reproduce
Steps to reproduce the behavior:
Try to send any mission, see depth is always n/a

Expected behavior
Estimated bottom depth to show shallowest point along the transect

Additional context
I will hold off on proposing any grand visions for how we might help operators manage bathymetry :). If we've decided this is what we want to do for now let's make it work, and if not let's just get rid of it?