One strategy to ‘gather’ an enormous specimen: easy photogrammetry within the discipline utilizing a cell phone
Impressed by the current glorious collection of articles by Trevor Watts discussing the sorts of Mid-Jurassic dinosaur footprints to be discovered alongside the Whitby coast (Deposits, Points 46, 47, 48 and 49), when just lately working within the space I (NL) made certain that I’d have the time to stroll the seashores from Saltwick Bay to Whitby. I additionally timed my work to ensure I might make use of the low tides early within the morning at first gentle. In addition to the same old ammonites, belemnites and plant fossils, I discovered a handful of single footprint casts (most too heavy to aim to maneuver) and a few very good fallen slabs of claw marks and partial trackways – additionally principally too large to maneuver. One slab particularly stood out among the many others on the backside of the Ironstone Ramp in Lengthy Bight (Figs. 1 and a pair of) – a ‘double trackway’ from what appear like two fairly totally different beasts strolling in parallel – though they had been probably fashioned at totally different instances. Within the type of raised footprint casts slightly than precise indented footprints, the specimen included 5 good prints within the left monitor and 4, probably 5 prints, heading in the right direction – so every monitor contained a ‘full set’. Though the tracks look superficially fairly totally different from each other, each look like attributable to theropod dinosaurs.
The slab was not buried within the sand, however sat on another fallen blocks so might be seen in its entirety. Nevertheless, at about 1.2m x 1.0m x zero.2m, it will need to have weighed in extra of 500kg. To ‘gather’ it, one choice was to interrupt it up and take it away in items in a number of visits and put it again collectively once more at a later date, however that may have been lower than excellent to say the least and small fragments may need been misplaced. A preferable choice would have been to hold the whole slab all the way in which again to Whitby in a single piece, requiring a gaggle of individuals strolling alongside the seaside at low tide. The primary 5 metres or so would have been a tough scramble over all the opposite fallen blocks whereas carrying the heavy weight, however it might have been attainable to do that comparatively safely by utilizing beams of wooden to lever the slab fastidiously onto a robust pallet, then sliding the beams contained in the pallet and carrying it away ‘stretcher’ vogue – if sufficient folks and time had been out there. Nevertheless, ‘Storm Doris’ was about to hit and the probabilities had been that the specimen could be damaged into items by the subsequent day. Even when it survived the storm, it was attainable that, though most individuals discovering it might admire the specimen, perhaps take images after which go away it the place it was, another person would possibly take a hammer and chisel to it and attempt to take away the nicer of the raised footprints on the left facet of the block.
The best choice – which didn’t preclude returning at a later date with a gang of individuals to gather the specimen for the native museum if it survived the storm – was to take as many images as attainable there after which to file the specimen. This could contain not simply taking the images with one thing included for scale (in addition to the compulsory ‘selfie’) however taking images from as many angles as attainable from roughly the identical distance, together with across the again and beneath so far as attainable, particularly so photogrammetric 3D digital mannequin might be manufactured from the specimen at a later date. The issue was that the one digicam I had on me was a slightly previous ( about 2013?) and cheapish cell phone with restricted reminiscence. So I took 65 images with this. I returned the subsequent day to seek out that the specimen had fortunately survived Storm Doris and I took 81 extra images, this time with a correct digital digicam (a Canon Powershot SX50 HS).
Not solely did this imply that the double trackway was effectively recorded earlier than it obtained broken, however it additionally meant that two digital photogrammetric fashions might be constructed, one from every set of pictures. It will even be fascinating to check the 2 fashions to see if the previous cell phone digicam would supply one thing helpful or whether or not this kind of photogrammetric work can solely be achieved with a ‘correct’ digital digicam. To make sure the most effective likelihood of excellent digital fashions being made out of these pictures, I despatched the images to Steven Dey, a photogrammetry, laser-scanning and 3D-printing skilled at ThinkSee3D primarily based in Oxfordshire, with whom I’ve labored on many palaeontological tasks earlier than. Under, he describes the processes of constructing the 3D digital fashions, in addition to giving high suggestions for taking good photogrammetry images within the discipline.
Photogrammetry (also called SfM – Construction from Movement) generates digital three-dimensional fashions from a number of pictures taken from totally different positions and angles round an object. A bonus of photogrammetry in contrast with different strategies, equivalent to laser scanning, is that the ‘scanning’ a part of the method could be very price efficient as all that’s wanted is a digital digicam to seize the information and even a cell phone digicam will do. This implies it is a perfect technique to be used within the discipline, when out taking a look at massive specimens and geological options. It’s even attainable to take correct measurements of the ensuing digital 3D specimen and to measure options, notably helpful if the specimen itself was tough to entry. To make sure this, place a scale bar or an object of recognized measurement (a geological hammer, hand lens or trowel for instance) on the specimen in a number of pictures to behave as a reference and this can enable the digital 3D mannequin to be made with a related scale. You may also put a color scale within the scene, so the colors of the phototexture could be color balanced if you need correct color replica.
Casual comparative trials have proven that the accuracy of digital 3D fashions of fossils produced with photogrammetry could be equal to and even higher than different scanning strategies, however this accuracy depends on 4 predominant influences: (1) the standard of the pictures; (2) the standard of the sunshine within the setting; (three) the floor high quality of the specimen; and (four) the processing of the photographs right into a 3D mannequin.
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The standard of the pictures
Most issues are widespread to all pictures, equivalent to decreasing digicam shake (a tripod can assist), good focus and an applicable publicity to minimise over-exposed or under-exposed areas. Nevertheless, some issues are notably related to the photogrammetry course of, equivalent to ‘depth of discipline’. Indirect angled pictures throughout a specimen, particularly a protracted object, could be partly out of focus as a result of a restricted depth of discipline if care is just not exercised, so keep away from overly indirect pictures. ‘Shutter precedence’ could be a helpful setting on a digital digicam for photogrammetry, as this permits the ‘f’ quantity to be tuned to maximise the depth of discipline.
Distance from the topic can also be value contemplating. Usually, with a normal 50mm lens, a distance of round zero.5m or so works effectively. Too shut and lens distortions could cause points. Too distant and the decision of the photographs – and due to this fact the decision of the eventual mannequin – shall be diminished. The decision of the digital mannequin is immediately associated to the space from the topic, and to the scale and backbone of the picture sensor within the digicam. An ‘auto’ setting on the digicam can usually be an applicable facility to make use of, however it can be an issue if very totally different brightness ranges are skilled in numerous areas of the specimen, for instance, sharp variations in gentle and shade on a sunny day. Hardly ever are circumstances excellent within the discipline, so it’s value making an attempt a number of configurations of digicam settings if there’s time and, you probably have such choices, taking take a look at pictures from totally different angles and reviewing them earlier than taking the ultimate set of pictures all on the identical setting.
A particular departure from regular pictures is the necessity to seize a number of images from quite a few angles across the topic. Each angle of the specimen that must be scanned needs to be captured with an 80% overlap between images. Fig. three reveals the assorted positions (the blue rectangles) of the cell phone used to mannequin the trackway slab on the coast at Whitby. To have captured the entire of the specimen, it might have been essential to scan one facet first, then flip it over and scan the underside, however this might not safely be undertaken with such a heavy slab. For example, nonetheless, this was simply achieved for the 32kg single sauropod footprint solid collected on the identical day utilizing simply 45 images (Fig. four).
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Gentle high quality
The proper circumstances for taking pictures for photogrammetry functions are vivid diffuse gentle, equivalent to being exterior on a cloudy day within the spring or summer season, as altering gentle, darkish shadows and/or vivid daylight on surfaces are usually not excellent. Highlights from vivid daylight have a tendency to maneuver place between totally different pictures, and shadows obscure the floor colors and texture of the specimen. Each of those would result in ‘noise’ and inaccuracies within the remaining 3D mannequin. If indoors, use subtle daylight from home windows or synthetic ‘daylight’ lighting, or set the digicam to compensate for electrical lighting.
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Floor high quality
Photogrammetry works greatest with extremely textured topics. It doesn’t work on very shiny objects, or clear or very monochrome objects. For instance, a really plain white wall wouldn’t scan, because the algorithms in photogrammetry must see options ‘transferring’ from picture to picture to find out depth. If these options don’t exist or reflective highlights transfer between pictures, the method of constructing the digital mannequin will fail. The highly-textured floor of fossils, equivalent to footprints and their surrounding rock is especially suited to photogrammetry, because the algorithms concerned depend on variations in floor colouration and texture to recreate the 3D geometry.
- Processing the photographs. Processing the information effectively requires a pc with a fairly excessive specification, equivalent to my (SD) Intel i7 with 32Mb RAM and a superb GPU card (for instance, NVIDIA). Even then, processing pictures into 3D fashions is a particularly computing-intensive course of, usually requiring many a whole bunch of thousands and thousands of calculations. So, if there are numerous images, it’s typically vital to cut back the decision. Photogrammetry software program can assist by permitting the information to be damaged into blocks to course of it in smaller units and thereby not overwhelming the pc’s assets multi function go. The software program we used was Agisoft Photoscan normal version.
Weaknesses in any of the above 4 elements can result in ‘noise’ within the remaining digital mannequin or decrease decision of element, or, in excessive circumstances, failure to create the 3D mannequin. It’s normal for a few of these elements to be imperfect, so compromises need to be reached, however the photogrammetry course of itself is kind of sturdy and may typically address fairly poor inputs. In affordable circumstances, a lot bigger specimens than the footprint slab could be captured this manner, even massive geological options and certainly complete landscapes. Digital 3D fashions may even be made out of pictures taken underwater, taken by drones or different aerial pictures and even microscopic photogrammetry is feasible – so long as sufficient good high quality pictures are taken in good circumstances. However 3D mannequin processing issues need to be accounted for. It’d take many hours to course of a really massive set of pictures right into a 3D mannequin, relying on the specification of the pc.
The entire scene of the Whitby footprint slab as a 3D mannequin with out the color overlay is proven in Fig. 5. The output of the method is successfully a 3D of the scene. The feel file overlays a number of picture pictures on to the 3D geometry including knowledge on the floor colouration. Wanting on the mannequin with out the color overlay can typically reveal morphological options which are in any other case arduous to tell apart.
Three digital fashions had been created of the slab containing the trackways at Whitby. The primary mannequin (Fig. 6) was made out of images taken with the previous cell phone (65 pictures on a GT-I8190N digicam on a 2014 Samsung Galaxy telephone). The second mannequin was made out of images taken with a compact SLR digicam (81 pictures on a Canon Powershot SX50 HS four.three). A 3rd mannequin was made by combining these two units of knowledge. In all circumstances, the diffuse and fixed gentle on the specimen from naturally vivid however cloudy circumstances was excellent.
The pictures had been loaded into Agisoft PhotoScan and rendered into 3D fashions following the workflow within the utility: aligning images, constructing dense level cloud, constructing mesh, and constructing texture. All processes had been set to prime quality and decimation within the mesh construct was averted by utilizing a customized mesh measurement set to a excessive worth. PhotoScan performs digicam calibration robotically utilizing Brown’s distortion mannequin, however the images had some EXIF knowledge, which assists the calibration and digicam alignment course of. The feel file was a jpeg set at four,096 x four,096, utilizing Photoscan’s generic texturing technique. The completed 3D fashions had been exported from Photoscan as an OBJ file, with related materials and photo-texture file, and uploaded to the web 3D viewing and sharing platform, Sketchfab, for sharing and dialogue (see hyperlinks beneath).
Readability of each fashions was discovered to be of top of the range, displaying millimetre scale particulars of the trackways within the 3D geometry and within the connected texture file. The digital SLR digicam would often produce a greater outcome than the cell phone digicam, as a result of the standard of the optics and backbone of the sensor means it will probably seize extra data. Nevertheless, the newest cameras in cell ‘smartphones’ are actually very superior and may make glorious photogrammetry instruments. In poor gentle circumstances, they’ll even produce higher outcomes than mid-range SLR digital cameras. Additionally they have the benefit of being a lot less complicated to make use of.
Within the case of the Whitby trackway, images taken with the previous cell phone produced very practically pretty much as good a outcome because the digital digicam and the mannequin was definitely greater than satisfactory as a file, and for identification and measurement functions.
In conclusion, capturing a number of pictures of an in any other case uncollectable object within the discipline with an previous cell phone digicam can allow a scientifically helpful 3D digital mannequin to be constructed to file the specimen and from which measurements could be taken. This knowledge may even be used to 3D-print a displayable strong reproduction of the fossil, if required. Cell phone cameras are bettering yearly so outcomes utilizing this system are going to get even higher.
The digital fashions mentioned could be discovered at these addresses, however they is likely to be gradual to open:
The mannequin made out of cell phone images can considered right here:
https://sketchfab.com/models/f39f252079e54ffdb4a8a983fac07319
The mannequin made out of the digital SLR digicam images could be considered right here:
https://sketchfab.com/models/9da00f96836b46fc8d2d999420da496b
The photogrammetry course of was additionally undertaken for the only sauropod footprint solid, utilizing simply 45 images to seize the whole specimen, together with the underside (Fig 5). This mannequin could be considered right here:
https://sketchfab.com/models/d332d02574c546539bcc175227313dd7
Concerning the authors
Nigel Larkin is a contract palaeontological conservator, preparator and curator, whose analysis pursuits embody hint fossils and ichthyosaurs. Steven Dey runs ThinkSee3D, an organization specialising in digital and bodily 3D realisation tasks for analysis and public engagement (together with 3D printing, AR and 3D scanning).
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