Abstract
Three-dimensional (3D) surveying and modelling of the underwater environment is challenging; however, it becomes even more arduous when the scene or asset to measure extends from above to underwater through the water surface. While this is topic of high interest for a number of different application fields (engineering, geology, archeology), few solutions are available, usually expensive and with no guarantee of obtaining homogenous accuracy and resolution in the two media. This paper focuses on a procedure to survey and link the above and the underwater worlds based on photogrammetry. The two parts of the asset, above and underwater, are separately surveyed and then linked through two possible analytical procedures: (1) independent model adjustment or (2) relative orientation constraints. In the first case, rigid pre-calibrated rods are installed across the waterline on the object to be surveyed; in the second approach, a synchronized stereo-camera rig, with a camera in water and the other above the water, is employed. The theoretical foundation for the two approaches is provided and their effectiveness is proved through two challenging case studies: (1) the 3D survey of the leak of the Costa Concordia shipwreck and (2) 3D modelling of Grotta Giusti, a complex semi-submerged cave environment in Italy.
Highlights
Measuring natural and man-made structures in three dimensions (3D) across the water surface is a very challenging task, yet necessary for a large number of applications ranging from marine infrastructures, civil engineering, cultural heritage, biology, civil protection, forensics, and many others.While on land, 3D surveying techniques are routinely applied with success, meeting different accuracy requirements, underwater, because of physical characteristics and complexity of operations related to water medium, systematic mapping has been achieved only partially and with more relaxed accuracy requirements if compared to land measurements
This paper focuses on a procedure to survey and link the above and the underwater worlds based on photogrammetry
The photogrammetric methods here presented would allow to significantly reduce the overall time Tahnedprheloattoegdracmosmtsetwriicthmaetmhoudcshhmeroerepreeffisecniteendt wdaomuladgaellaoswsestosmsiegnntifaicnadntrleypraeidriuncge othpeeroavtieornalsl
Summary
Measuring natural and man-made structures in three dimensions (3D) across the water surface is a very challenging task, yet necessary for a large number of applications ranging from marine infrastructures, civil engineering, cultural heritage, biology, civil protection, forensics, and many others. 3D surveying techniques are routinely applied with success, meeting different accuracy requirements, underwater, because of physical characteristics and complexity of operations related to water medium, systematic mapping has been achieved only partially and with more relaxed accuracy requirements if compared to land measurements. Eng. 2020, 8, x FOR PEER REVIEW passive sensors to photogrammetrically determine both the submerged and emerged parts of the othbejeocbt jienct3Dina3nDdawnidthwciothlocroilnofroirnmfoartmionat.ioTnh.eTmhetmhoedthsoadlsoawlsoorwkoinrkciansecathsee tohbejeocbtjiesctnoist nstoitlls, tailsl,foars efoxramexpalme ipnlecaisne coafsfleooaftinflgoaotbinjegctos bsjuecchtsasupcohnatosopnos,nsthoiopnss,,asnhdipflso, aatnindg fwloiantdintgurwbiinneds.tuTwrboindeisff.eTrewnot pdrioffceerdenutrepsrbocaesdeduroens pbhasoetdogornamphmoettorgyrarmempreetsreynatreedp: resented: 11. TThhee bbooaatt,, aa sseemmii ssuubbmmeerrggeedd oobbjjeecctt iinn flflooaattiinngg ccoonnddiittiioonn ccaann bbee ssuurrvveeyyeedd wwiitthh oonnee ooff tthhee ttwwoo pprrooppoosseedd mmeetthhooddss uussiinngg rreessppeeccttiivveellyy ffoorr mmeetthhoodd oonnee ((aa)) ssoommee ssppeecciiaall lliinnkkiinngg ttaarrggeettss fifixxeedd oonn tthhee hhuullll ((ee..gg..,, wwiitthh mmaaggnneettss oorr ssuuccttiioonn ccuuppss)) oorr ffoorr mmeetthhoodd ttwwoo ((bb)) aa ssyynncchhrroonniizzeedd sstteerreeoo ccaammeerraa ppllaacceedd wwiitthh aa ccaammeerraa bbeelloowwaannddaaccaammeerraaaabboovveetthheewwaatteerr. Details of the relative orientation procedure for joining the above and underwater surveys of the ‘Grotta Giusti’ semi-submerged cave system based on a synchronized stereo camera are reported and discussed
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