Flying a Bench with a Drone

Key Rules and Flight Prep

Key Rules to keep in mind before flying a bench:

At least two third of photos should be taken with the camera pointing straight down (nadir images).
Take photos along passes with at least 70% - 80% Overlap.
Good results have been previously obtained with flight heights between 75 ft, 150 ft and 250 ft.
Need to overshoot at least 20 feet around the target area to be mapped to avoid any stitching or reconstruction issues around the edges.
Fly the drone forward and with the camera tilting forward by 5°. When surveying the next pass, turn the drone instead of flying backward. This helps improve reconstruction quality.

Flight Prep:

Establishing a good connection: Make sure the satellite maps and front cam are loaded in the drone flying app once the drone is synced.

Check Satellites: Check the number of satellites that the GPS can see in the app. 13 satellites or more give the drone GPS good enough accuracy for geo-referencing. Best practice: Give the app a minute after startup for the IMU sensors on the drone to settle and satellites to catch on.

Gauge measurements of the bench: First time pilots or when flying on a new bench one should try to make a manual flight up to the bench height and to the end points of the region to be mapped, to check altitudes, height of the bench, camera angles and camera views. All these values can be measured using the drone flying app.

Note:

Higher the flight height => less number of images => less pixel detail on the model and 2D map
!!!! Lot of images does not mean better model -> only means more processing time !!!
To check overlap -> Pick a point on the image and count to make sure it is in 5 photos as you fly, if not, adjust speed and intervals at which the picture is taken

Taking Nadir/Top-view images

Flying the top of the bench

Depending on how wide the shot is make at least 3 nadir passes along the rows, flying at 75 ft or above, measured from top of the bench. Every hole must be in at least 2 passes.

Make sure at least 3 of your nadir passes cover some of the bench top and some of the floor.

It's critical to get a good set of nadir photos to create an accurate model. At least two thirds of the pictures uploaded for any project must be nadir pictures.

Key Points:

In above images the arrows indicate the passes made.
In above images the overlapping boxes denote the range of vision of the camera that is captured in the images.
Pass 1: Make sure you cover some part of the floor (not too much) looking down in one of the passes (blue colour coded pass). This helps the image stitching process.

Flying the floor of the bench

Depending on how much detail is needed and how much area is to be covered at the bottom of the bench make 1-3 nadir passes at the bottom of the bench, flying at 75 ft or above from the top of bench (process is similar to flying the top)

Getting the right Oblique Images

What should the oblique images look like? Getting the right angle for oblique images?

Depending on the height of the bench make 1-2 oblique passes across face (Usually one pass is fine unless there are significant overhangs)

Key points:

In above image the blue box denotes the area captured in the oblique images.
For more than one pass take the images at different altitudes and angles.
Avoid capturing the horizon in the images.
Ensure first 2 rows and floor are in all shots. This gives the system an area of the image for stitching the oblique images with nadir images. Denoted by Red box in above image.
Ensure you can see under any overhangs.

Good results have been previously obtained with camera angle being around 40-50 degrees, but the angles should be adjusted based on the number of passes and the height of the bench.
Flight height should be adjusted based on the field of view of the drone camera and the height of the bench.