Photogrammetry is the art, science and technology of obtaining reliable information about physical objects and the environment through practices of recording, measuring, and interpreting photographic images and patterns of recorded radiant electromagnetic energy and other phenomena.

In the following interview with the researcher Prof. Dr. Murat Egi shares the practical advice for fast and efficient 3D modeling using underwater photogrammetry with examples of a case study and benefits of using a tablet device underwater.

About the author

S. Murat Egi is an Electrical Engineer (BSc) and completed his MSc and Ph.D. studies on Biomedical Engineering on “The Evaluation of Altitude Decompression Procedures and Development of New decompression Strategies”. He organized the first National Underwater Science and Technology meeting in 1996 in Istanbul. He planned and directed 7 high altitude diving expeditions where 500 dives were performed at altitudes up to 4000 m and has articles on decompression modeling and diving research published in several proceedings of EUBS (European Underwater and Baromedical Society) and UHMS (Undersea and Hyperbaric Medical Society). References: https://www.researchgate.net/profile/Salih-Egi-2 

Lidar vs photogrammetry

Lidar and photogrammetry both have revolutionized how professionals across industries gather, map, and analyze geospatial data. While both technologies are different, lidar method is more expensive and well-suited for the “active” or real-time data collections, whereas photogrammetry benefits from surveying at the expense of passive data collection. Photogrammetry uses imaging captured by a camera to reconstruct the terrain in an accurate 3D model using image overlap and sufficient ground control.

Getting started

In every dive, you typically follow the diver’s guide. However, in photogrammetry, specifically underwater photography in practice, a precise plan is essential. This includes deciding where to start and end in the site location. As a diver, having good buoyancy skills is crucial. For post-processing and reconstructing 3D images, a powerful computer is necessary, which I’ll explain later. Never attempt it for the first time during a dive; instead, practice at home with simpler objects like your TV, chain, or car on land. It won’t take more than a few minutes or half an hour.

Baseline

• 1 dive with 50min bottom time (for a 30m long wreck)

• Minimum photo skills

• Minimum computer literacy

But

• Very good planning

• Perfect buoyancy

• Powerful computer for post processing

• Practice on the land

These are the four key skills. To make it more practical, we recommend using a tablet. Underwater, a tablet provides a large display, alleviating concerns about high photography skills. A tablet’s large viewfinder is the key, or alternatively, a mobile phone. Housings for mobile phones are widely available in the market.

Stay perpendicular to object planes whenever possible

• Multiple passes for multiple planes if possible

• Object distance 1-2m for higher resolution on a standard lens

• Lower distance increases the scan time that results in higher resolution

Be patient and maintain a distance of one to two meters. Closer proximity requires a higher scan time, impacting resolution. Start with lower resolution, keeping a distance of around 2 meters, depending on visibility. Using a tablet housing naturally avoids camera shaking, ensuring stable photographs. Move slowly, taking pictures with at least 40% common area between consecutive shots. Complete a 360° circle for each perpendicular surface, then return and shift 45° for the next circle.

Move to a higher position than the subject

Create an angle of approximately 45 degrees between the subject and continue shooting from the same spot. Turn 360 degrees around the object until you reach your starting point.

Setting your camera or mobile phone to automatic mode with a one-second interval is suggested. Use software that allows taking pictures every second, ensuring a smooth process. Complete the 360° circles, and once done, proceed to the second row, Part 2 of the process.

Part 2 OBJECT reconstruction

adobe.ly/3xot6NN

This second part involves software packages for linking photos and creating a 3D model. Software costs range from free to $4500 per year. Starting with a free one is recommended. Sketchpad is interesting, allowing you to sell your 3D models in a market.

SW options

Software	OS	File type	Mobile Access	Price
Acute 3D Viewer	Windows	.obj, .fbx, .ply, .osgb	No	Free
Adobe Dimensions	Windows/MacOS	.obj, .stl, .fbx, .glb	Yes	30$ / month
Sketchfab	Web based	.obj, .stl, .fbx, .glb, .ply	Yes	80$ / month
Trimble Sketchup	Web based	.obj, .stl, .fbx, .glb, .ply	Yes	300$ / month
Autodesk 3ds max	Windows/MacOS	.obj, .stl, .fbx, .glb, .osgb, .ply, .dae	No	4500$ / year
Blender	Windows/MacOS	.obj, .stl, .fbx, .glb	No	Free

Options on Resolution

With 200 photos, a draft can be created, linking 100 photos and 2500 points in about 50 minutes for a good computer. Standard processing may take up to three hours. For higher resolution, it might take up to 25 hours, requiring caution not to overwork your computer.

Options	Draft	Standard	High res
Total Photos	200	200	200
Aligned Photos	104	188	198
Total Points	2500	52000	166750
Elapsed Time (min)	47	185	1500
Size (kb)	2950	16865	32850

1 hour https://adobe.ly/3q6L3Om 

3 hours https://adobe.ly/3iS0g4e 

25 hours https://adobe.ly/3wsHF2Q 

Use cases- Environmental

The final result after processing can be impressive. You can produce your own dive site maps, promote your dive sites, and help with environmental projects, or sell or use the 3D models creatively. This technique was applied to our project for the European Union in Cyprus. We did the 3D scan of the reef so by repeatedly doing it, it would be possible to understand what is the environmental damage. With 3D dimensions it can be then printed with 3D printers, you can put the reef on your desktop, take a print out of the rag or the reef or whatever you want, or you can engrave it into the glass for unique displays.. And moreover, by working on a Sketch app to place it in the market to sell it. So it’s practically stable.

You can print the 3D model or engrave it into glass for unique displays. Consider selling your creations on Sketchpad.

Underwater Malta: A virtual museum for underwater cultural heritage with Nick Coertze

Underwater archaeological sites are out of sight and more often than not out of mind. The reason for this situation is simple – the physical barrier created by the sea itself- where only divers or people in submarines are able to visit such sites. Through this virtual museum you now have the opportunity to explore these historic time capsules.

Now, our unit was set up as a way to preserve the sites better from a cultural heritage management point of view. Over the last few years, we’ve released 22 dive sites to the public with the goal of releasing one to three more every single year. This allows people to physically dive these sites, while those unable to do so can explore them virtually through the museum.

The commonality among all the wrecks is their depth limitation, ranging from 55 meters to 110 meters. This poses a challenge of “out of sight, out of mind” for those who don’t dive, as well as for policymakers who may not witness the sites firsthand. We closely collaborate with experienced divers who assist in monitoring the wrecks for illegal activities, ensuring the preservation of these historical sites.

The release of the museum marks the final step in a complex process. Beginning with remote sensing, target validation, and diverse surveys, we process the data to create digital assets. This includes 3D models, videos, and images that are then launched on the virtual museum.

Identification of underwater archaeological sites

Identification process utilizes AUVs (Autonomous Underwater Vehicles). They follow a programmed “lawn mower” pattern to capture data, providing us with a comprehensive view of the sites. If we don’t know what’s there, we can’t effectively protect, conserve, or manage it. Take, for example, the HMS Urge, a British submarine located at a depth of 110 meters. Once identified, divers survey the site, and we create 3D models and other digital assets, which we share with the public.

Virtual site employment

We employ various initiatives, including outreach to schools with virtual reality goggles, providing a glimpse of these underwater wonders to non-divers. We also create artist’s impressions, snapshots of wrecks placed on seabed backgrounds, for promotional purposes on social media platforms.

The wrecks, showcased on the virtual museum, include 3D models ranging from three-meter deck cannons to shipwrecks and plane wrecks at greater depths. Users can explore these wrecks and even view them in virtual reality through the website. We continually update the models, such as a large wreck off the coast of Gozo, spanning 65,000 square meters, which we study annually to expand our understanding.

Taking the case study of the HMS Urge, we presented condensed information on the wreck’s introduction and key characteristics. This allowed users to delve into much detail of the object. Once the website was ready, we launched it along with relevant information on social media platforms, sharing discoveries and commemorating events like finding the HMS Urge after being missing for 80 years. Link to the online museum: https://underwatermalta.org/discover/hms-urge/ 

To enhance the experience, we offer flythroughs, providing both divers and non-divers with an impression of what it’s like to explore these sites with the access to extension of VR headsets to explore the wrecks. Beyond cultural significance, studying wrecks in detail through imagery and videos contributes to biological and conservation research.