The Show Must Go On

The world has changed since the last update. Plans with the UWIS GPS kit have been put firmly on hold and the IANTD Underwater photogrammetry course have been postponed. All of these are frustrating but on the scale of things a very minor inconvenience.

Not everyone is locked down and sat at home. By its very nature commercial fishing has been self-isolating for generations and the boats at Weymouth remain active. One of them recently snagged and landed a large three-bladed aircraft propeller. Knowing Deeper Dorset‘s keen interest in aircraft the fisherman gave Grahame Knott a call.

Bit of a Snag

With a find like this the natural desire is to jump in the car and nip down to Weymouth to shoot the images for a 3D model. With lockdown thats just not going to happen. But a small change to Grahame’s daily exercise meant walking past where the propeller was stored so why not ask Grahame to gather the images?

Armed with a GoPro and some guidance on technique Grahame shot a few minutes of video of the propeller and took a few measurements. The content was then imported into Metashape. With a small subject processing didn’t take too long but there were a few issues at the tip of one of the blades.

A thin section such as a propeller blade requires special handling

Blue Sky Thinking

Metashape will always look for points and try to extract as many matches as possible but occasionally this causes problems. In this case the background has been mismatched with the tip of the propellor.

There is a tool in Metashape that helps prevent problems like this. Masking the source images forces the software to examine only areas of interest.

Adding a mask tells Metashape to ignore the area and not look for points

With the unwanted areas masked out the model was processed again and this time a much cleaner result obtained. This will not fix the issue of managing thin sections but it has tidied up the blade tip.

The finished model of the propellor. Enough detail in the hub confirms the identity

The tip of the blade won’t really help with the ID of the aircraft type but the hub will and there was plenty of detail there.

ID Confirmed

With just a single blade bent the engine was not running when the aircraft ditched. The length of the straight blade and the design of the hub has confirmed its from a Lancaster bomber. Which means there should be another three propellers and the remains of a four engined bomber somewhere in Weymouth Bay. Where is the rest of the aircraft?

There have been rumours of such a wreck for decades but never confirmed. Rest assured Deeper Dorset will be on the case of the missing bomber as soon as we can.

1 thought on “The Show Must Go On

Comments are closed.