Geo Referencing the UB 116

Earlier this week Kevin Heath of Sula Diving kindly towed his side scan sonar fish past the remains of the UB 116, generating a very clear image of the wreck site:

Marked up sonar image of UB 116. Image courtesy Kevin Heath/Sula Diving

Relating the Model to the Planet

With the GPS positions recorded in the sonar we can now extract a few key points and add them to the model. We do need a minimum of three, with more generally being better. Each of the arrows in the image above relates to a common point we can identify between model and sonar. The GPS values were duly noted, and we added the corresponding points to the model.

View from the South East, looking over the site of UB116.

Matching the Model to Sonar

Photoscan Pro has a really useful import function that can read masses of GPS data in CSV format, or you can enter the values individually.

Agisoft Photoscan Pro importing GPS from a CSV

With the values updated and the model revised we can then generate the Digital Elevation Model (DEM) and the geo referenced ortho photo. Other formats include Google Earth files too if required, but here’s the DEM:

Digital elevation model of the UB116.

Big Data

As Photoscan can generate massive ortho photos (see Photogrammetry – Managing the Data) we took the decision to wind down the accuracy a bit and generate a TIFF image we could actually open and use. That said, we do have to reduce the image size by quite a lot to make it usable. And checking the stats of how most viewers access the page, mobile phones seem very popular…a 4Gb TIFF image may be a bit much… The result of which shows us the layout of the wreck, with north being at the top of the image:

In case anyone has not seen the model, here’s a link:

Records and Guides

We now have a scaled and GPS referenced site plan of the UB 116, a record of what the wreck site looked like at the time of scanning. A very efficient way to capture and preserve a wreck, which as we know from experience can change over time.