A Google form was set up to collect answers from each participant to the seven following questions:

1. What is your current position?*1
2. What field of research do you consider yourself involved in?*1
3. What ecosystem(s) does your work relate to?*2
4. How long have you used photogrammetric models for?*1
5. What aspects of photogrammetry do you particularly intend to focus on during the workshop?*2
6. Any additional comment?*3
7. What platform do you usually use to perform photogrammetry?*2

N.B. All questions required an answer from the survey participant.

All participants consented to share their answers anonymously. The total answer rate was 84.4% (54 participants out of the 64 registered).

1. What is your current position?

Most of attendees belonged to academia (~ 80%; Fig. 2), with a relative balance between early-career scientists (BSc/ MSc, PhD and post-docs; 44.5%) and permanent researchers (35.2%). Still, 9.3% of participants were engineers.

2. What field of research do you consider yourself involved in?

Geologists, biologists/ecologists and mappers predominated (90%; Fig. 3) in roughly equal proportions, reflecting the general GeoHab conference's focus. The rest was mostly made of subgroups of one to two people (e.g. marine energy, computer sciences).

3. What ecosystem(s) does your work relate to?

Most of the attendees’ work focuses on the marine environment (from the littoral to the deep sea; Fig. 4). A large share of attendees were identified as having experience in the sublittoral ecosystem (0-200 m depth). Still, the deep-sea realm was well represented with 44.4% working in bathyal and with 18.5% working in abyssal waters. Seventeen responders (31.5%) work on both sublittoral and bathyal environments.

4. How long have you used photogrammetric models for?

Half of the participants had no experience at all with 3D photogrammetry (Fig. 5). Still, 35.2% had less than two years of experience with photogrammetry. This overall ‘lack of experience’ demonstrates the relevance of this workshop as photogrammetry has become more relevant over the past decade (Pulido Mantas et al. 2023).

5. What aspects of photogrammetry do you particularly intend to focus on during the workshop?

Answers from participants showed a relatively balanced interest amongst data collection, model computation and result extraction (Fig. 6).

6. Any additional comment?

From a selection of comments:

• “Suggestions on best software (affordability vs. quality) would be very helpful, also if we came away with generic workflows”.
• “How to make the most of available data that was gathered without using any controlling methods (e.g. laser pointers, stabilisation)”?
• “How can we get an orthophoto from georeferenced images” (x2)?
• “I am interested in QPS SfM or QGIS Plugins”.
• “I am interested to know more about using AI or programming for post-processing and analyses” (x2).
• “would be interested in ‘filling the gap’ nearshore between where multibeam stops and terrestrial mapping starts”.
• “Calibration/bundle adjustment and georectification”.

Comments highlighted that the workshop duration was not sufficient to approach deeply enough all aspects of photogrammetry. However, those comments provided valuable information for modulating the hands-on session and the panel discussion (e.g. first comment on standardisation of photogrammetry and selection of software).

7. What platforms do you usually use to perform photogrammetry?

A balance predominated amongst the use of drones (33.3%), scuba diving (29.6%) and the use of underwater platforms, such as remotely operated vehicles (20.4 to 24.1%), towed cameras (40.7%), and, surprisingly, the more recent technologies of autonomous underwater vehicles (33.3%; Fig. 7).

Presentations during the workshop allowed participants to discover a wide range of acquisition platforms (e.g. aerial to underwater; Fig. 10). Objects imaged varied from man-made structures, geomorphological facies and different biological scales of interest (e.g. from sessile individuals to communities). Applications ranged from the use of photogrammetry to investigate spatial organisation and to monitor temporal dynamics of man-made structures or biological communities and to raise awareness of local population regarding their marine ecosystems. All presentations emphasised the importance of photogrammetry that provides centimetric-resolution of investigations needed for various ecological applications, such as growth monitoring in natural conditions or after disturbance, characterisation of topographically complex habitat and species co-existence to investigate niche partitioning.

Ranked preference between three hands-on was requested to each participant during the pre-event online survey. Based on their preferences, we assigned them to a hands-on stand that was run by one person or a group (Fig. 8):

• Isabel Urbina-Barreto, Simon Delsol and Clément Delamare;
• Vincent Mahamadaly & Alexandre Sneessens;
• Loïc Van Audenhaege & David Price.

The activities of the hands-on stand were defined by the stand leader(s). However, we encouraged the stand leaders to coordinate themselves to offer a similar content structure despite featuring different environment and acquisition platforms. Content similarities included display of image acquisition, mesh acquisition and manipulation of the mesh (e.g. Figs 11, 12). Some stands proposed extra activities, such as mini ROV piloting in the hotel swimming pool and visualisation of a shipwreck using virtual headsets.

As an example, for reproducibility purposes, the hands-on activities of Loïc Van Audenhaege and David Price is presented below:

1. Prior to the hands-on, a scene was created. Sand and fragments of different shapes were collected. After the workshop, fragments were put back in their original locations to comply with the environmental regulations;
2. Attendees first collected 42 images with a camera and from different angles of view and zooms of the scene. We advised that the stand leader checks carefully that shading on the scene is limited by the light position and participant standing location;
3. While images were being copied on the processing computer, participants could have an extra activity (e.g. piloting of mini ROV) and participate in discussions;
4. Participants then attended the processing of a 3D mesh on Agisoft displayed on a projector: feature extraction, image matching, sparse cloud computation, mesh creation, texturing and scaling. For each of the steps, the output was checked and explained (e.g. camera optimisation: check of features matched and discarded in different pairs of images). For pointcloud, mesh and textures, a file .txt, .obj and .jpg + .mtl were respectively extracted and their content and structure was displayed with notepad. The resolution of the final model was also investigated (e.g. number of vertices per m²). By zooming in and out on specific areas, we provided an idea on the resolution of the output (i.e. how many details were captured);
5. Once the model was exported in .obj, we loaded it on CloudCompare. We first taught participants how to navigate throughout a 3D model in the CloudCompare virtual environment. The mesh was subsampled in a pointcloud from which the normals were extracted and orientated. Slope, orientation and roughness were computed with different kernel radii to highlight the importance of defining a set of Kernel radius number(s) as it will ultimately constrain the scales of investigation for testing particular hypotheses. Statistics (e.g. histograms) of those descriptors were displayed. The output was saved as a .txt file to demonstrate the ease of using that workflow in R for multivariate analyses;
6. Throughout the hands-on, questions were freely asked by the participants who showed interest. Answering actually took most of the time needed to run the hands-on which encouraged us to provide a dynamic hands-on (in the future?). Interesting questions came up, such as what the regular time of processing is, what software do you advise etc.

We briefly displayed other tools of Cloudcompare, such as the ICP and point-to-point registration algorithm to overlay models together. Although time did not allow it, we intended to load the 3D model on Meshroom and Codemap to display alternative and opensource photogrammetry software. Originally, we also intended to load data in Meshlab. This software includes algorithms that Cloudcompare does not hold, such as for remeshing algorithms to lower mesh resolution and fasten the display of results.

Due to time constraint, the panel discussion only lasted 40 minutes:

• What (developing) technologies could complement underwater photogrammetry to acquire high-resolution mapping? Sonar, Lidar and the hyperspectral camera in development were mentioned;
• Practical aspects of scale integration of photogrammetry were discussed, notably with sonar dataset acquired at much lower resolution;
• The differences between using SfM and colour band ratios to calculate bathymetry.

A Google form was set up to collect answers from each participant on the seven following questions:

1. Now that you know better photogrammetry, do you think it could be a valuable tool for your work (if you were using photogrammetry before, please answer N/A)?*1
2. Do you now feel confident enough to be able to run a 3D reconstruction on your own (if you were using photogrammetry before, please answer N/A)?*1
3. Do you think that some aspects photogrammetry remained unclear or should have deserved more time?*1
4. Feel free to comment your answer.*3
5. Do you think that some aspects of photogrammetry were too extensively detailed?*1
6. Feel free to comment your answer.*3
7. On a scale from 1 (dissatisfied) to 5 (highly satisfied) by 3 (neutral), how clear were the presentations?*1
8. Do you think of anything that could improve the presentations?*3
9. On a scale from 1 (dissatisfied) to 5 (highly satisfied) by 3 (neutral), how satisfied were you with the hands on?*1
10. How would you improve the hands on?*3
11. On a scale from 1 (dissatisfied) to 5 (highly satisfied) by 3 (neutral), how satisfied are you with that workshop?*1
12. Do you think of anything missing or that could be improved for that workshop?*3

N.B. All questions required an answer from the survey participants.

All feedback participants consented to share their answers anonymously. The answer rate was of 34.4% (22 participants out of the 64 registered).

1. Now that you know photogrammetry better, do you think it could be a valuable tool for your work (if you were using photogrammetry before, please answer N/A)?

From the 22 participants that answered the survey, 15 did not use photogrammetry prior to this survey (Fig. 13). From those 15 participants, 13 considered photogrammetry to have potential for their own work after the workshop.

2. Do you now feel confident enough to be able to run a 3D reconstruction on your own (if you were using photogrammetry before, please answer N/A)?

Despite the workshop, 10 beginners out of 16 still required supervision for photogrammetry (Fig. 14). This reflects the difficulty to adapt the workshop for beginners when working with time constraints. While we intended to provide an overview of the overall workflow, there remains space for them to play with their own data to empower them even more. Still, one participant attempted a reconstruction by his/her own after the workshop.

3. Do you think that some aspects of photogrammetry remained unclear or should have deserved more time?

A majority of 10 responders pointed out the need to investigate more the software from pre-processing to post-processing (Fig. 15). Five attendees found that all aspects were clear enough.

4. Feel free to comment on your answer.

• “A handout for the software usage (a “cheat sheet”) for a simple case”;
• “Data quantity, best practice for handling large datasets”;
• “Practical acquisition and processing of ROV data”;
• “Short time frame and high number of people”;
• “The hands-on session covered aspects that remained difficult to understand only with presentations”.

5. Do you think that some aspects of photogrammetry were too extensively detailed?

Overall, 17 participants considered that no aspect was too extensively detailed (Fig. 16).

6. Feel free to comment your answer.

• "The level of detail was good".
• "This workshop provided a great overview of photogrammetry applications".

7. On a scale from 1 (dissatisfied) to 5 (highly satisfied) by 3 (neutral), how clear were the presentations?

With a weighted average score of 4.41/5, the audience was satisfied about the presentation clarity (Fig. 17).

8. Do you think of anything that could improve the presentations?

• "More time for interaction between speaker and the attendees was needed";
• "Difficulty to see and hear";
• "Presentations on software".

9. On a scale from 1 (dissatisfied) to 5 (highly satisfied) by 3 (neutral), how satisfied were you with the hands-on?

With a weighted average score of 4.23/5, the audience was satisfied with the hands-on activities (Fig. 18).

10. How would you improve the hands-on activities?

• Give the option for attendees to discuss with the stand mentor what they want to practise;
• Smaller groups and not having groups in the same room were recommended several times;
• Providing more details on software functionalities during the hands-on session was recommended twice. More time for the hands-on and the possibility to attend different stands was also raised.

11. On a scale from 1 (dissatisfied) to 5 (highly satisfied) by 3 (neutral), how satisfied are you with that workshop?

With a weighted average score of 4.55/5, the audience was generally very satisfied of the workshop in overall (Fig. 19).

12. Do you think of anything missing or that could be improved for that workshop?

• A cookbook was recommended;
• Possibility to participate to all group activities was also recommended;
• Giving the possibility for participants to bring their own data was suggested in order to discuss photogrammetry under various case studies and practicalities and help the audience to deal with their data at the same time;
• For a next edition, longer discussion panel (e.g. 2 hours) is suggested to better identify the needs and the challenges that the growing photogrammetry community will likely face in the future (e.g. data publication standardisation, novel acquisition technologies, generalisation of open-source photogrammetry software).