The Art of Knowing

Knowing where you are underwater is high-value information. That feeling of being lost is something every diver has experienced and every dive project has suffered from it. Not knowing where you are reduces efficient use of all too precious in-water time and the recreational dive industry uses dive guides to partially solve the problem.

We are not predicting the demise of dive guides just yet…but site knowledge will not be quite the same if you are equipped with underwater GPS…

No Knowledge – No Problem!

The UWIS navigator has been busy adding scale and reconstruction to 3D models but thats only part of the value. With the tablet displaying the ortho photo navigation skills are reduced to being able to look at the screen, point the tablet where you want to go and swim. The diver is guided to where they need to be and live feedback will quickly correct course errors.

As discussed previously, the location of the helicopter is known but the 2017 data would not align with the current set. We needed to scan it again and finding it a good test navigation. So why not give the tablet to a diver who freely confesses to not diving Vobster much and has no site knowledge?

With the tablet displaying an ortho photo of the site swimming directly to the helicopter was easy – just follow the line.

Which is exactly what we did. Marine biologist Claire was handed the tablet and given the job of navigating us to the helicopter. In 10m of gloomy visibility the as-the-fish-swims distance of 62m is enough to get lost in several times over. The tablet was good to its word and Claire lead us straight to the site.

Dense Cloud vs Depth Maps

We have touched on this subject before and its worth revisiting as several of Vobster’s dive attractions benefit from depth map mesh creation. Anything with thin sections and high detail typically reconstruct better with depth maps and the Vobster Escort and Helicopter are two such examples.

The car model including its interior aligned and meshed perfectly first time. However, the helicopter and its interior proved troublesome. Thanks in part to previous divers the port cockpit area was surrounded in a plume of silt and bad vis. This meant a half dozen images in that area failed to align and parts of the interior were bulging through the fuselage. The model was…less than pretty…

Confidence is Everything

There is a new view option in Metashape 1.6 for the model – Model Confidence. This is a great tool for understanding the mesh but also for learning about camera overlap and how to avoid gaps.

Model Confidence view in Metashape – visualising the surface and highlighting where reconstruction might need some more attention

Disabling the internal images got rid of the unsightly growths breaking through the external skin. The solution is to examine the model and reshoot those critical areas with red highlights, making sure the exterior skin is sound. The ability to learn, understand and correct just got a lot easier.

Coffee Time?

While the helicopter was being scanned Claire spent most of the time using the tablet to navigate around a site never seen before. The recorded track shows exactly where Claire headed whilst at all times knowing the shortest route back.

The helicopter now sits into the rest of the referenced model. Scale and geo location is inherited from the main chunk. The model is not finished so remains aligned but not merged.

With the helicopter task done Claire navigated back to the entry point in record time. I think its fair to say the tablet and its use as a navigation and recording tool was a big hit…we got to site, did the scan and got back to the exit nearest the burger van by the shortest possible route.

We might even be able to persuade a marine biologist to dive in quarries more often with this kit – such is its power!

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