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:
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.
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.
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:
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.