NUPG 8th April Meeting Report

This month Alex Tasker gave us an insight into photogrammetry and his journey so far using this technique underwater.

Our usual focus at NUPG is capturing the beautiful scenes we see underwater in 2D, so turning these images into something in 3d so you can move around an object or underwater area on your laptop is a different concept and style of photography. Alex explained some of the history and theory of how this works and explained how he first got interested in this style of photography.

The historical side of things took us back to the thousands of images taken from spitfires in WW2 and the intelligence techniques that spotted the V2 rocket project. Alex’s own journey with photogrammetry first started with East Cheshire Sub Aqua Club’s Highball project and their aim to create a 3d model of one of the highball bombs in Loch Striven to allow non-divers to see what we are able to visit.

The theory started off making things sound relatively easy. The aim is to take lots of overlapping photographs of the subject from different angles. If there’s enough overlap each photograph has common points which the software can identify. The software can use both stills and video (by extracting individual frames from the video) and has the potential to use images from multiple sources to create the final 3d model, so the options on what camera to use are wide. After identifying the points in each image that match those in another image in the set and passing through multiple phases the software (hopefully) pops out a 3d model. Alex’s first attempt was encouraging, on our ‘NUPG warm-up’ day in Capernwray last year he took hunderds of photos of Thunderbird 4 and produced a good 3d model (he obviously had 2 very patient buddies). Taking the photos that allowed this first attempt to work seemed easy, there was plenty of natural light and good visibility, the lesson learnt on this particular occasion was more about the patience required waiting for a laptop to process the images (or grind to a halt as the case may be). With the aim of the highball in mind though he needed to target objects in bad visibility, leading to trips to other well-known quarries where bad visibility and gloom are more readily found and an attempt to get a model of the hydrobox at Stoney Cove. The visibility on that occasion was so bad that the software thought some of the ‘muck’ in the water was actually part of an object and attempted to make it part of the model! This experiment also highlighted the challenges of getting images aligned, in bad visibility you need more overlap. The resulting model worked well for the top of the hydrobox but not the sides unfortunately. As with any form of photography though, practise is the key, so I’m sure another trip to the hydrobox will be on the cards this year.

At the beginning of March, Alex headed to Vobster Quay for a weekend to take part on the IANTD Photogrammetry course run by Tim Clements. He thoroughly enjoyed the course and got to pick up some tips from the likes of Simon Brown and Marcus Blatchford, who have a wealth of experience on this subject and have produced some amazing models (including entire wrecks and models that combine both underwater and drone photography). The course also got Alex thinking about the use of ‘angel lighting’. He’d been using his regular camera for the stills and attaching a video camera to the rig to collect additional data, having strobes and video lights on the same rig did add complications. By having his buddy carry the video lights it made using the video camera easier as a backup, gave his regular camera a better chance to focus and helped him easily know exactly where to find his buddy (not to mention giving his buddy something to do so she doesn’t get bored!)

Getting the images for photogrammetry is something any of us could do with our existing cameras. The challenges then become the amount of data generated from those images and the amount of processing power needed to turn them into a 3d model. There’s an amazing amount can be achieved by doing this though, from creating models of coral reefs to showing non-diving experts details of underwater wrecks. It will be interesting to see where his journey takes him over the coming months.

The monthly competition theme was Cephalopods. We had an array of fantastic images; the overall winner was Justin Beevor’s coconut octopus.

Overall Winner April 2019 – Coconut octopus by Justin Beevor

Congratulations also go to Glynn Phillips whose octopus shot came in 2nd, and Maggie Russell who took 3rd place with a nicely isolated squid and also won the Compact category with her octopus entry.

Second place in the open category went to Glynn Phillips
Maggie’s squid claimed 3rd place in the open category
Maggie Russell won the compact category with this lovely octopus

Comments are closed.