Architectural photogrammetry

Hi. I don’t know if something like this has already been asked or addressed. I am an architect and do conservation and restoration, and we are now increasingly being asked to do expeditious surveys with photogrammetry. Usually, I do terrestrial photogrammetry (with SLR), but for the past few months I have a Mini 3 Pro that I have been using for drone photogrammetry, flying manually or doing hyperlapse (orbit or trajectory) to capture facade details as well. Sometimes, however, I need to have some context around as well.

If I wanted to use Litchi Pilot (which I have already used to fly), would it be possible to set up a grid mission where at each waypoint the drone stops, takes 4 photographs by rotating 90°, and then continues to the next waypoint? That way, I would only have to set up one mission to take 45° photographs of the architecture and context. So far, I have seen (if I have not misunderstood myself) that I can only rotate with respect to the relative position of the drone, so when it changes direction I also have to change by how many degrees it rotates, and if the grid is, for example, rotated with respect to the object, I also have to calculate the degrees with respect to the grid angle and it is a bit complex.

Grid flights is something we are working on adding

Assuming you are using waypoint actions to rotate the drone’s yaw, the angle you specify for the waypoint action ‘Rotate Drone’ is relative to north, it is not relative to the drone’s current heading/direction

Thank your for your answer! So, it could be useful to have the same heading for every waypoint (e.g. 0° that should be North); in this way I should have the same set of actions/movement for every waypoint. Then, I need to do the following actions for every waypoint:
Take photo
Rotate 90°
Take photo
Rotate 180°
Take photo
Rotate 270°
Take photo
Rotate 0°

Is it right? Will the drone stop at every waypoint, take 4 pictures and then go to the following waypoint? For the grid I’m using a tool ( Grid Mission Designer), export csv and then planning on Mission Hub.

Yes, that is correct. In Grid Mission Designer you would want to have Zcheck=1 which will cause there to be a waypoint at the location of every picture. By default, Grid Mission Designer will captre only one photo per waypoint. Once imported into Litchi’s Mission Hub, you will need to select all waypoints (Select all…), then modify the actions to match what you listed above. This can be done in one step using batch mode.

Thank you! I’m also wondering about GSD in this tool. There isn’t the Mini 3 Pro to select as device/camera and I can’t see any control about the fly height. So, what about the waypoints height and GSD? When I import the grid in Litchi Mission Hub, I need to adjust the height and so also the GSD I selected is not considered anymore.

You’ll notice that the GSD slider controls the flight altitude since they are directly related. The flight altitude is shown in meters and feet.

The closest drone model to the Mini 3 Pro in the tool is the Mavic Air 2. Similar camera specs. It will work for your purposes.