Feature Request (AC mission planning): Option in Grid to hold level at each camera trigger point

For those doing survey missions with nadir-line cameras who can't or won't put a gimbal on their copters, the images will always be more or less oblique due to the forward motion of the copter, along with any pitch/roll to hold the course if there is wind present (as there almost always is). Even if the copter is delayed at each waypoint to allow for imaging, there will still be platform tilt to hold position. A nice feature would be the ability to build a waypoint list where the copter stopped and hovered level at each camera trigger waypoint, i.e., did the equivalent of a switch to ALT_HOLD and ignored holding GPS station during the few seconds needed to grab an image or two. The amount of drift off course during this short time is a small price to pay for better quality nadir-line images. Currently there is no way to do this short of manually switching back and forth from AUTO to ALT_HOLD and back to AUTO and letting the copter resume course. You'd still have to fold the camera triggering into this as well, potentially with a delay after arriving at the waypoint (and switching to 'hold level') before triggering the camera. Also, as this would materially slow down the mission, the total time calculator would have to factor in these delays, along with the associated acceleration & deceleration before and after each 'hold level' period.

Start by tracing Mission Planner's waypoint-list, camera-trigger, flight-mode, and mission-time-calculation entry points; the issue names no files or tests. Determine how a waypoint could request a level hover, when triggering should occur, and how drift, acceleration, deceleration, and added delays affect the total mission time. Done means the behavior and timing are represented consistently in planned missions.

Written by the indexing model from the issue text.