Photogrammetric 3D reconstruction of the Santo Antonio de Tanna shipwreck from legacy photography

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Abstruse

This chapter explores the significance of legacy information equally a source of new information and the possibility of extracting new information from sources of data that were recovered before the advent of computers and the digital revolution. Since so, much of the accent has been directed towards gathering new data and at that place has been little emphasis on records that engagement back over 50 years. This chapter examines ii examples: the first the Cape Andreas Expedition in Cyprus 1969–1970 and the other the
Santo António de Tanná
excavation 1977–1980. Both case studies are examined for the elements of photography that can be used to excerpt new information and how information, in the futurity, can be all-time be collected to suit these developments.

Keywords

  • Cape Andreas
  • Cyprus
  • Republic of kenya
  • Legacy data
  • Portuguese frigate

  • Santo António de Tanná
  • Shipwreck survey

Introduction

This chapter underlines the significance of legacy information as an important source of new data. The legacy information described in this chapter was nerveless in the late 1960s and 1970s. This was a fourth dimension before desktop computers and GPS, when underwater cameras were just becoming more available and the underwater archaeological world was in its infancy. It is interesting to recall that, in those days, locating underwater archaeological sites was exceedingly difficult. Position could merely be adamant close to shore where country transits were the most reliable method and to some extent yet are today, although they suffer from a lack of permanency. Additionally, where a survey track was required, horizontal sextant angles was the cheapest, although by far the nearly difficult method to use. Once out of sight of country, there was cipher bachelor to the archaeologist, other than diverse offshore commercial electronic positioning systems, such as HiFix and MiniRanger; well across the budget of most archaeological projects. Surveying underwater archaeological sites was too hard. Essentially, survey piece of work relied on trilateration or simple offset surveys using tape measures and there was near no possibility to piece of work in 3D as the only available calculating systems available, at least in the early 1970s, was the slide-rule and log tables. Photography in the field was also difficult. Movie cameras could only have up to 36 pictures before they required reloading; processing and printing in the field was difficult, as a dark room with processing facilities and an enlarger were required. This was the environment where the legacy information described in this chapter was collected.

This chapter deals with two projects that the author was involved in and which have been selected to illustrate the processing of legacy data. The showtime project was at Greatcoat Andreas, Republic of cyprus, which was the first archaeological project the writer directed. The objectives of this project were based on the author’s previous experience working with George Bass at Yassıada in Turkey and later on with Michael Katzev on the Kyrenia digging. After Cape Andreas, the writer came to the Western Australian Museum and conducted the excavation of the Dutch East India shipwreck
Batavia. The processing of the legacy data from that shipwreck is the subject of a PhD thesis and will not exist discussed hither (McAllister 2018). In 1978–1979 the photographic survey of the Portuguese frigate
Santo António de Tanná, wrecked in Mombasa harbour in 1697 was undertaken. The two projects will be discussed in more than detail below; all the same, some background to the two projects is required. Every bit the primary objective of Greatcoat Andreas piece of work was to locate and survey underwater archaeological sites, information technology presented an opportunity to investigate and explore new techniques and applied science. At that fourth dimension the underwater swim-line survey technique had simply recently been developed, and the
Admiralty Manual of Hydrographic Surveying
(Hydrographer of the Navy 1965) provided data on maritime survey techniques. An experimental underwater theodolite was constructed to try and amend underwater site surveying. Photographic techniques were investigated using the Nikonos camera with refraction-corrected lens, which had merely simply become available. Bass et al. (1967) had adult an underwater photomosaic system at Greatcoat Gelidonya and Williams (1969) had published
Elementary Photogrammetery, which introduced a range of photogrammetric techniques that could be applied underwater. With this range of techniques, the Greatcoat Andreas project was undertaken.

The Mombasa survey, on the other mitt, was a much more than specific projection. The hull of the ship was uncovered during the 2 seasons of digging, and the objective was to record this in gild to produce a site plan. Past the belatedly 1970s, technology had progressed. Programmable calculators were bachelor; the Nikonos photographic camera now had a xx mm underwater-corrected lens and the author had worked in Australia to develop a stereo-bar photo tower to record sites. These techniques were used to record the complex hull structure of the
Santo António de Tanná.

Every bit it turned out. both projects subsequently provided an opportunity to reassess the information. With the advent of computers, Geographical Information Systems (GIS), satellite imagery and programs that immune the data to be reprocessed, the subject of this affiliate turns to examine the information collection methodology, the reprocessing of the data and the outcomes. While much has been published on the recent apply of underwater photogrammetry with digital cameras, the author has found no references to published work on retrospective or legacy photogrammetric analysis for maritime archæology. This is surprising every bit information technology is an expanse with huge potential. This is now beginning to be recognized the field of archeology (Wallace 2017) and palaeontology (Falkingham et al. 2014; Lallensack et al. 2015).

Greatcoat Andreas Expeditions

In 1969 and 1970, the Oxford Academy Research Laboratory for Archaeology conducted two underwater archaeological survey expeditions to Greatcoat Andreas, Cyprus (Fig. 3.1), to tape underwater archaeological material including shipwreck sites and anchors. The sites were plant using a swim-line search technique, and they were then surveyed and photographed. The results were the subject of ii publications (Light-green 1969, 1971b). This material has lain fallow and only recently, with the advent of a number of computer-related techniques, has now been reassessed. The positions of the sites, although accurately recorded on topographical maps at the time, did not take geographical coordinates, making it almost impossible to relocate them in the future. Using the original data, it has been possible, with the use of satellite imagery and the Esri ArcGIS programme, to precisely locate all the sites and attribute approximate geographical coordinates (latitude and longitude) to them, ensuring the possibility of relocation in the time to come (Fig. 3.ii).

Fig. iii.1

Map of Cyprus showing Greatcoat Andreas and the Khlides Islands

Full size image

Fig. 3.2
figure 2

Plan of Cape Andreas showing sites and breadth and longitude filigree created from GIS

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The possibility of revisiting the data for these sites is due to the fact that both of these early on maritime archaeological expeditions featured experiments in underwater photogrammetric techniques, which at that time were in their infancy. The expeditions used the relatively new underwater Nikonos 35 mm camera with a 27 mm water corrected lens to create photomosaics and to record sites and objects. The photographic data has now been reprocessed using
Agisoft PhotoScan/Metashape
and has resulted in some remarkable 3D plans of the sites.

The writer had been involved in the Cyprus Archaeological Underwater Survey Expedition (Crusade) that had visited the Cape in 1967, with a squad from The Academy Museum, Pennsylvania and the Oxford University Research Laboratory for Archaeology (Greenish et al. 1967), and as the area seemed to exist promising for a hereafter survey it was selected for the project. The main objective of the Cape Andreas expeditions was to survey the seabed around the Greatcoat and Khlides Islands for wreck sites and other archaeological textile. Every bit the water clarity around the Cape often produced visibility of effectually 70 one thousand, the survey planned to use a swim-line technique with divers swimming at a depth of around 20 grand visually searching the seabed up to a depth of l k. The divers were spaced at regular intervals on a line and then that adjacent divers could see the same surface area, thus ensuring the seabed was systematically searched.

As in that location were no detailed hydrographic charts of the Cape Andreas area, the get-go priority of the 1969 expedition was to produce a detailed chart of the Cape delineating the l m contour. To do this an repeat sounder was used to measure the depth and the position of the survey vessel was recorded using horizontal sextant angles to stations on the islands and Cape. Equally there were no survey points on the chain of islands extending from the Cape, the most detailed plan, at that time, was an aerial photograph. Therefore, the survey piece of work had to commencement from scratch. Using a theodolite, a serial of prominent survey stations on the islands were established that could exist seen from the sea. Once established, the survey vessel fabricated a serial of runs perpendicular to the shore recording the track of the vessel with the horizontal sextants. Each sextant ‘ready’ was marked on the sonar paper trace and subsequently the data transferred to the plan. This enabled an authentic program of the depth contours around the Cape and an gauge of the swim-line survey work that needed to be undertaken (see Fig. 3.three).

Fig. iii.3
figure 3

Hydrograph nautical chart of Greatcoat Andreas produced from survey conducted in 1969

Full size epitome

In one case the vessel survey was completed, the swim-line surveys were undertaken, one time again using horizontal sextant angles to plot the positions of the swim-lines. Dissimilar swim-line techniques were used in 1969 and 1970 and the results are shown in Fig. 3.4. Once a site was located, it was photographed and surveyed. At the large wreck sites, photographs were taken in gild to create a photomosaic. To do this sparse platted ski rope (selected considering of its depression stretch) marked at metre intervals, was laid out forth the long axis of the site. This was used as a scale and to assistance the photographer ensure that the site was adequately covered. It was, past coincidence, this technique proved to be the nigh successful in processing the legacy information. The picture show was developed on-site. Images were printed and then manually laid up to create a photomosaic.

Fig. iii.4
figure 4

Swim-line surveys of 1969 and 1970

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From the results of the ii years surveys a big quantity of information was obtained from the swim-line work; this fabric was divided into 3 categories:

  1. 1.

    Wreck sites with ceramics, including material that may perchance exist jettison;

  2. two.

    Anchor sites-areas where anchors were closely associated; and

  3. three.

    Private anchors.

Wreck Sites with Ceramics

A total of ten pottery sites were located; some sites are little more than than objects from spillage or jettison (Sites 1, 14 and 18). Sites 12 and xvi; Sites 10 and fourteen; and Sites 17 and 24 had material that appears to be interrelated and it is hard to make up one’s mind whether the sites represent separate or associated events.

Site 12, on the north side of the island No. 4, is clearly a wreck site. It consists of an area approximately 20 × 15 m containing numerous heavily concreted Corinthian-style roof-tiles and encompass-tiles. Effigy 3.5 shows a hand-laid up photomosaic of the site and Fig. 3.vi shows a drawing of the distribution of the sherds.

Fig. iii.5
figure 5

Photomosaic of Site 12 produced in 1970

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Fig. 3.half-dozen
figure 6

Drawing taken from the photomosaic showing the ceramic material

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Site 16, a few metres to the due south of islands Nos 4 and v, consisted of a scattered collection of concreted sherds of amphorae and tiles, together with a small concentration of small bowls and plates, many of which were intact. The tile sherds to the west of Tag 3 may represent material that has been washed over from the tile wreck, Site 12. It is difficult to plant if the two sites are associated and why such a big number (c. 25) of fine ware pottery objects should exist concentrated, relatively undamaged, in such a small area.

Site 28 was located a calendar week before the end of 1970 expedition. The superficial material lying at a depth of twenty m are Corinthian-mode roof-tiles and embrace-tiles (Fig. three.seven). The regular stacking indicated that the site was intact and represents the surface layer of cargo of a ship buried in a soft sand seabed. Two areas of tiles were noted. The larger surface area consisted of near sixty roof-tiles arranged in 4 rows, together with 8 cover-tiles; a further layer can be identified underneath these. The smaller area consists of about xv tiles (Dark-green 1971a).

Fig. 3.7
figure 7

Site 28

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Sites 17 and 24 prevarication around the north side of the second island; Site 24 was located past Crusade in 1967 and was further investigated in 1969 (see Green 1969, Figs. xi and 13).

Site x was located in 1969; it lies to the n of the rocks between the third and fourth islands. Information technology is i of the most difficult sites to analyse, as the material is spread out over a big rocky area, 50 × 20 m. A variety of amphora sherds of different types and periods take been noted and recorded (Green 1969, Figs. 7 and eight). The team members constructed a large-calibration mosaic of the site in order to try to produce a detailed plan. The initial impression is that this site represents spillage or jettison from several periods, rather than from several wrecks.

Site 1 consists of several looped handles and flat amphora bases concreted to the rocks around the southwest corner of the commencement isle. In view of the small number of amphorae, this site can only represent jettison or spillage.

Site 18 consists of looped handles and pointed feet of amphorae scattered over an area of 300 sq. one thousand. It is situated to the north of the small group of rocks off the south side of the Cape. In view of the considerable amount of pottery (and beer bottles) in the area information technology is probable that this has been used as a lee shore by ships since antiquity. The site therefore probably represents jettison of damaged amphorae from a ship sheltering and waiting for favourable winds.

Site 14 lies on the due south side of the rocks mentioned with reference to Site x. The site consists of a few tiles and amphorae, perchance jettison or spillage. It is surprising that out of the ten sites described, five consist mainly of looped-handle amphorae and four are tile sites. Sites 12 and 28 are clearly complete wrecks of ships carrying tiles as a cargo.

Anchor Sites and Individual Anchors

Four anchor sites were recorded on the due north side of the Cape Andreas. Two of the sites (23 and 26) were areas containing a large number of different types of anchors. Sites 23 and 26 were located at the point where the gently upwardly-sloping sand seabed changes to a steep stone cliff face. Site 23 has a total of 28 anchors: 18 iron, 8 lead and 2 stone. The positions of a total of about 50 anchors were recorded, just only about one-half were recorded photogrammetrically.

Reworking the Legacy Survey Data

As mentioned, in the tardily 1960s, surveying was limited to optical systems. Every bit was typical in those days, relative position was accurate, but absolute position, in normal circumstances, was about impossible to obtain. When accurate GPS first became available, most hydrographic charts needed to be corrected to conform to the absolute information. The plans produced in the 1960s, although accurate, therefore, could not be given precise latitude and longitude or be applied with any certainty to accurate modernistic maps or charts and could merely exist applied to big-scale Admiralty charts.

Using ArcGIS information technology was possible to georeference the plans produced in the 1960s that had used the outline features on the early aerial photo. Using the World Map in Arc GIS, it was and so relatively simple to place coastline features on the aerial photograph and the World Map and thus consummate the georeferencing. As the survey stations had been transferred to the plans these could then be located on the GIS. With this information information technology was possible to place all the survey data from the 1960s on the GIS and aspect them relatively accurate latitude and longitude coordinates. Thus, all the sites now take geographic coordinates with an estimated position accuracy of almost ±five thou (see Fig. 3.2).

Reworking the Legacy Photographic Information

A full of 69 black and white 35 mm films were taken during the expeditions representing about 1700 images. The images were assessed for suitability for processing using
Agisoft PhotoScan/Metashape
software. Initially, photos that were plainly unsuitable were rejected. This left photos that were mosaics of large sites and groups of photos of single or multiple objects such as anchors or ceramics.

Agisoft PhotoScan/Metashape

The images from Site 12 were selected commencement. Any image with a grid frame was rejected, as the filigree frames were moved around the site and, thus, fabricated the alignment for
Agisoft PhotoScan/Metashape
difficult (the option of masking the frames in
Agisoft PhotoScan/Metashape
was decided to be unnecessarily crushing due to the large number of photographs). In that location were 99 images in the data set that had originally been used to construct the photomosaic. These were run through a high-end workstation with 4 X7560 Intel®
Xeon two.26 GHz CPUs and 512 GB of RAM. The
Agisoft PhotoScan/Metashape
settings were at the highest possible resolution. The alignment took 20 min resulting initially with 25 cameras out of the 99 aligning, giving 54,347 tie points and a 3D model with around nine.five million faces (Fig. 3.viii). The 25-camera chunk was then isolated and the plan was re-run with the remaining 74 images. The second process aligned a further 23 cameras with xl,246 points, taking 1 h to build dense cloud and an hour to create the mesh (Fig. iii.8).

Fig. 3.8
figure 8

PhotoScan/Metashape ortho-photograph of Site 12

Full size prototype

A similar method was used on Site 10 producing a practiced quality 3D image of the site (Fig. 3.9). Attempts to produce 3D images of the anchors, nonetheless, were mostly unsuccessful partially because there were not enough photographs from dissimilar angles and in full general the photographs had a 3D grid frame included in the view that disrupted the processing.

Fig. 3.9
figure 9

Site 10 mosaic PhotoScan/Metashape

Full size image

The well-known trouble with
Agisoft PhotoScan/Metashape
is that the program is a ‘black box’ and running the program on the same set up of data produces different results on different occasions. In addition, there are many settings that tin can produce slightly different results. For the Greatcoat Andreas material, a number of different models were produced. In general, the photomosaic runs without grid frames were the nigh successful in converting to 3D visualizations, however, the masking characteristic in
Agisoft PhotoScan
is yet to exist tested on this cloth.

The
Santo António de Tanná
Shipwreck

In 1978 and 1979, photographic recording of the Portuguese wreck of the
Santo António de Tanná
(1697) was undertaken (Piercy 1976, 1977, 1978a, b, 1979a, b, 1981 & Sassoon 1982). The projection, nether the auspices of the National Museums of Republic of kenya and the Plant for Nautical Archaeology, involved the excavation of the transport that lay nearly 50 grand from shore under the walls of Fort Jesus, Mombasa, Kenya. The frigate
Santo António de Tanná
had been dispatched by the Portuguese Viceroy in Goa to relive the fort that was under siege by the Omanis. On inflow in 1697 the General anchored the frigate in front of the fort and was informed that all the Portuguese in the fort were dead and that nigh 25 Swahili men and 60 women were left defending the fort. The fort was immediately relieved, withal, some time later the vessel broke its moorings, drifted onto the shore and sank (Fraga 2007; Killman 1974; Killman and Bentley-Buckle 1972). The fort finally fell to the Omanis in 1698 after a three.5 year siege.

During the excavation of the site in 1978 and 1979 photographic recording was undertaken during periods of expert visibility (Light-green 1978). This situation corresponded with the High Water Leap Tides, which brought clear oceanic water into the river that ordinarily had low visibility (c. two–3 thousand compared with 10–fifteen m during the Loftier Water Springs).

The surveying techniques used to record the structure of the ship uncovered during the second season were based on the experience of the offset season and were devised to see the rather peculiar weather of the site. Since it was required to produce detailed 3D plans, both photogrammetry and standard measurement recordings were used. The nature of the site, notwithstanding, produced limitations in the application of both techniques. Poor visibility, except at high spring tides, precluded the abiding use of photographic recording. Too, poor visibility and tidal currents made tape measurements unreliable and it was difficult to establish an accurate baseline for recording purposes. Additional problems were encountered because of the peculiar orientation of the transport, which lay on a steep slope with its bow inclined xx° downwardly the slope and with a lateral tilt of 54° to port. The keelson was twisted along its exposed length, and there was prove at the scarf joint that the stern section, including the keelson, had moved in relationship to the bow. These distortions have been extremely difficult to sort out because of the unusual orientation and the lack of a useful datum, such every bit the base of the keel to piece of work from.

The overall shape of the construction was recorded by measuring profiles at 1 m intervals across the hull of the ship at right angles to the keelson. A stereo-photogrammetric survey over the whole of the inside of the transport was made and so that detailed information of the internal structure could be recorded. Control points were put in identify and surveyed so that the photogrammetric survey could exist related to the profiles and incorporated in the overall plans. Detailed measurements were also made of the keelson, which served as the base line for the survey. Fraga (2007) produced a plan of the site based on the tape measurements taken in 1978–1979 and related this to the contemporary seventeenth and eighteenth-century Portuguese naval architecture texts of Lavanha (1610) and Oliveira (1578–1581).

Profile Recording

The profiles were measured at 1 thousand intervals along the keelson using a circular 0.75 m bore, 360° protractor, graduated in half degrees and mounted on a bar measuring i m in length (Fig. 3.10). The bar was clamped to the upper (starboard) side of the keelson then that the airplane of the protractor was at correct angles to the keelson. A pin mounted at the centre of the protractor acted as a swivel for a 0.5 m length of thin string with a stirrup at the stop, through which a 10 m survey tape was threaded. The angle and the true distance were recorded against the tape number. Using this technique, it was possible to piece of work in poor visibility (c. 1 one thousand) fifty-fifty when the two operators were out of sight of each other. The overall method was fast and reasonably authentic. In a 61 min swoop, with experience, it was possible to practice two vi one thousand profiles consisting of a total of fourscore readings. Using a small-scale hand estimator (Hewlett Packard 25), the polar co-ordinates were converted to rectangular (or x and y) co-ordinates, which greatly facilitated the plotting of information. The results, when converted to rectangular co-ordinates, were plotted on graph paper. The accuracy of the technique was basically governed by the size of the protractor and was almost ±2%.

Fig. three.ten
figure 10

Circular protractor used to tape profiles

Full size image

Trilateration Survey

The survey of the control points was carried out by trilateration. The upper starboard edge of the keelson was selected equally the baseline. The control consisted of tags driven into the keelson and port and starboard extremities of the site at ii yard intervals. A 2 one thousand rod was clamped against, and at right angles to the upper edge of the keelson opposite each of the keelson controls. Measurements were fabricated to the three nearest controls on both the port and starboard sides of the site, from the base of operations of the rod and at the keelson, and the marking 2 one thousand above the keelson. Thus, for example, if the rod was at the 4 m keelson mark, 16 measurements were fabricated from the base and tiptop of the rod, 6 to the port two, iv and half dozen marks, vi to the starboard 2, 4 and 6 marks and two to the keelson 2 marking and 2 to the keelson vi mark. The offsets of the command marks on the keelson to the rod were measured, and the angle of the rod to the truthful vertical was measured using a carpenter’due south level. With this information, it was, at the time, nevertheless not possible to summate the 3D coordinates of all the control points. This was to come later, but at the time we were aware that there were means to do this and rather futile attempts were made using the programmable calculator.

Photographic Recording

Two Nikonos III cameras were mounted 0.five m apart on an aluminium stereo bar. The cameras were adaptable and provided with screws so that the vertical and horizontal tilt of the camera could exist adapted. Ii targets, with viewing holes through their centres were mounted 0.5 m autonomously on a levelled bar at about 5 yard from the levelled stereo bar. Using plane mirrors in place of the lenses, the stereo bar was adjusted and so that the image of the target in the mirror, when viewed through the corresponding target, coincided with the heart of the optical axis of the fixed photographic camera. This enabled the cameras to exist adjusted and so that the optical axes were accurately parallel and perpendicular to the stereo bar. The stereo bar was so mounted on the photo tower to exist used underwater and the cameras remained on the bar for the whole of the survey. At the end of each underwater session, the bar was removed and taken ashore, but the cameras remained on the bar and the motion-picture show could be extracted from the camera without disturbing the camera positions.

The photograph tower consisted of a 2 m2
base of operations graduated in 0.i yard intervals, with stays supporting a two k bar, 1.88 yard vertically above the base of operations (Fig. 3.11). The bar was synthetic so that, when the stereo bar was fitted to it, the optical axes of the camera lenses lay on the middle line of the base foursquare, equidistant about the centre of the grid. Fine adjustments were fabricated using the mirror system to set up the photographic plane of the stereo bar parallel to the airplane of the grid frame. With this organization, there was a photographic overlay over the whole of the 2 m filigree frame, the fifteen mm lens had, in fact a focal length in h2o of twenty.eight mm.

Fig. iii.11
figure 11

Phototower on site showing slope of site

Full size image

Table tennis balls on 0.v thou of white string were attached to the mid-points of each side of the grid frame. As these floated upright in water, it was possible to determine the orientation of the camera plane to the true vertical. The orientation of each pair of stereo photographs could be determined for reference purposes by extending the line of the strings to the nadir point. The line joining the nadir point to the primary point of the photo, gave the direction of the true vertical, and the ratio of the length of this line to the effective focal length of the photograph gave the tangent of the angle of the true vertical to the photographic camera centrality. In exercise, withal, the minor electric current that was ever nowadays prevented this from being constructive.

Photographic exposures were made by moving the tower at 1 g intervals, thus ensuring good end-lap between the stereo pairs although it was hard to ensure that the adjacent runs had good overlap. Using 2 plastic buckets for buoyancy the photo tower could exist moved around quite easily past one person, although for authentic positioning two people were required. Nifty care had to exist taken non to stir up sediment, particularly as almost photography was carried out at loftier water when at that place was little current. Considerable variation in the quality of photographs was noted over the three High-Water Spring Tide periods when this photogrammetric coverage was carried out. This was due partially to the variation in the quantity of suspended matter in the water and also to the lite level caused by the effects of clouds and the fourth dimension of day. In many cases the coverage was a compromise, specially as the best visibility conditions, corresponding to the highest tides, cruel just later on dawn or just earlier sunset, when the calorie-free levels were also low for expert results. Under normal circumstances, using FP4 rated at 400 ASA and given twice normal evolution in D76, exposures ranged from f2.8 at 1/30 to f5.6 at one/60.

Considerable planning was required in preparation for the High-Water Spring Tide periods when this blazon of photogrammetry was possible. The timbers had to be cleaned of whatsoever silt, sand and other material that collected as a natural effect of the dirty h2o and stray discharge from the airlifts. If possible, airlifting was terminated about an hour before high-water, and the timbers were and so brushed to remove the fine silt. No other diving was carried out during the photographic runs to prevent disturbance of the fine silt in other areas on the site. The photomosaic was created past printing the images and then gluing them down on a paste lath (Fig. three.12).

Fig. 3.12
figure 12

Handmade photomosaic

Full size paradigm

Agisoft PhotoScan/Metashape

The most meaning trouble with processing the
Santo António de Tanná
material in
Agisoft PhotoScan/Metashape
has been the presence of the photo tower and table tennis balls. Because the belfry was placed on the interior surface of the hull, the orientation of the tower, in relation to the Cartesian coordinates of the hull of the ship, was different in each photo-pair.
Agisoft PhotoScan/Metashape, thus, has the problem that in each photo there is a belfry frame in exactly the same position and a view of the hull in a random orientation. Piece of work on the material has proceeded over the years since the introduction of
Agisoft PhotoScan/Metashape
in 2010 and results have slowly improved. A major breakthrough occurred thanks to a series of photographs taken using the stereo bar past itself without the tower. On ane particularly clear solar day, the bar was swum at a loftier distance over the site and a series of stereo photographic pairs were recorded. These were run through
Agisoft PhotoScan/Metashape
and a expert 3D model was obtained (Fig. 3.13), however because of the tiptop, the resolution is not particularly good.

Fig. iii.thirteen
figure 13

Perspective view of 3D model created in PhotoScan/Metashape

Full size image

Currently a project at Curtin Academy’s HIVE has simply been completed where the photographs and survey data were combined to develop a loftier-resolution orthophotograph (Fig. 3.14) and a DEM (Fig. 3.fifteen). Using the masking technique in
Agisoft PhotoScan/Metashape, the tower and the table tennis balls were removed, and a loftier-quality mesh has been achieved, although with some holes in the coverage (see Shaw 2018).

Fig. three.14
figure 14

High resolution orthophotograph created in PhotoScan/Metashape past HIVE

Full size epitome

Fig. 3.fifteen
figure 15

A Digital Acme Model (DEM) showing control points produced by HIVE

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In improver, the stereo pairs were processed to create individual models that were stitched together to produce a different arroyo to obtaining a 3D model. Essentially the objective of the project is to discover a method of processing stereo photographic coverage to produce a 3D model. This will have enormous implications for legacy photography and a method of reassessing excavations.

Conclusions

The ultimate question is what does the 3D visualization of legacy information do for the archeologist? It is obvious that visualization of a site in 3D is interesting and has a considerable significance in presenting the underwater archaeological world to the public. It remains less articulate, however, what the implications are for the archaeological world. One significant issue is the ability to obtain an orthomosaic of a site, which compared with the hand-produced photomosaic—made by laying up paper prints of images and matching them—is a pregnant improvement in accuracy. Working with 2d prints of a site with any significant 3D component is always a compromise. The power to produce an othomosaic and, thus, create a plan that is geometrically correct is significant in the interpretation of the site, particularly equally most site photographs have scales included. The orthophotograph can easily be scaled as the survey lines are marked in metre intervals thus providing an overall site scale. It is thus possible to make a count, catalogue and measure the artefacts on the site, something that would be virtually incommunicable with the paper-based photomosaic.

The question of 3D measurement of a site is more complicated. In the case of Cape Andreas, the sites were relatively flat so 3D measurements were less important. The situation with the
Santo António de Tanná
is much more interesting. The 3D model of the site is surprisingly detailed and enables almost any measurement from the site to exist obtained. For example, the control points on the keelson, 1 thousand autonomously is shown in Fig. 3.16 as 98.seven cm, this, because that the photography was taken 40 years ago, is quite remarkable. This particular aspect of accurateness in a 3D model is currently under farther investigation and volition be the subject of a after report.

Fig. 3.xvi
figure 16

Detail of PhotoScan/Metashape model of
Santo António de Tanná
keelson showing 3D measurement between two control points

Total size prototype

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Acknowledgements

The author would like to acknowledge the data supplied past Lachlan Shaw, the Curtin University intern, who worked on the
Santo António de Tanná
projection every bit part of a grant from the Australian Enquiry Council Linkage Grant
Shipwrecks of the Roaring 40s
(LP130100137). Also, Andrew Woods, Petra Helmholtz, David Belton and Joshua Hollick from Curtin University HIVE who supervised this project. I would similar to thank Robin Piercy, the managing director of the
Santo António de Tanná
project for providing the photographic record of the site. Last, thank you goes to Patrick Baker and the Cape Andreas squad for their assist and support.

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Green, J. (2019). Legacy Data in 3D: The Cape Andreas Survey (1969–1970) and
Santo António de Tanná
Expeditions (1978–1979). In: McCarthy, J., Benjamin, J., Winton, T., van Duivenvoorde, W. (eds) 3D Recording and Estimation for Maritime Archaeology. Coastal Research Library, vol 31. Springer, Cham. https://doi.org/10.1007/978-3-030-03635-5_3

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