The ADUS DeepOcean team have long maintained that a wreck survey presented as a digital terrain model (DTM) is not the most appropriate way of visualising the data because the inevitable ‘binning’ of survey points has a detrimental impact on survey resolution. This is rarely a problem when dealing with seabed topography and DTMs are an effective way of presenting bathymetry and that is why it is popular with hydrographic surveyors.
Another common problem is the ‘curtaining’ effect that masks data beneath overhangs making wrecks look as if they have hulls with vertical sides and which can completely conceal the true shape of a man-made object. Below is a photograph of a 3” 50 calibre gun on the liberty ship Jeremiah Obrien afloat in San Francisco Harbour, together with a typical DTM visualisation of the same type of gun on the wreck of the liberty shipwreck, Richard Montgomery, together with a basic point cloud of the original survey data. The later is considerably more informative than the DTM.
ADUS DeepOcean fund research into visualisation of survey data at the University of Dundee under the guidance of Prof Chris Rowland, one of the founding directors of ADUS. In conjunction with John Anderson, who developed the original WreckSight 3-D interactive software, he exploited the fact that point-clouds becomes easier for the brain to interpret if the data can be moved.
Other advances by Chris and his colleagues include placing 3-D occlusion objects within point clouds so that they are no longer transparent as the surveyed points on the far side of a cloud are masked. When this is combined with a sophisticated approach to ‘colour ramping’, where intensity or colour changes are aligned to one or more significant axis, a wreck or other structure can become much more lifelike and so easier to understand compared to colourful lumps on the seabed that are so often used to visualise shipwrecks.
The techniques developed for visualising shipwrecks is readily applicable to other man-made structures on the seabed and, to reflect this, the latest generation of our 3-D interactive software is now called ADUS Visualiser.
A recent ADUS DeepOcean advance has been the development of applying a surface to a complex 3-D point cloud. Below is an image of a subsea protection structure made by applying a surface to point cloud survey data.
Although this looks like an ‘as built’ image generated from construction data, it is a true ‘as is’ survey where a surface has been applied, then appropriately shaded, to indicate precisely what is present on the seabed. These data can then be used to produce a solid model from a 3-D printer, as below.
When the surface is removed from the survey data, two point clouds derived from slightly different viewpoints can be produced using a variety of image separation techniques. These can then provide a 3-D stereo image.
Another recent development is the combining of construction drawing (general arrangements) with the survey data into one point cloud. In this way it is possible to quantify accurately any damage to a ship’s hull or superstructure. Below are examples from the Costa Concordia showing the survey data sliced off at Deck 9 combined with the GA drawing and also a plan view detail showing forward damage to cabins on the port side.
I have, and remain, a keen supporter of ADUS and the high resolution surveys that you have performed.
ADUS has brought something novel to the industry and wherever it is exhibited, it has drawn interest as I am sure you know.David Pockett - Marine Consultant LOC Marine & Engineering Constultants