Day 8: Triangulation and trilateration

Today was already the third day of our campaign on the OVM 10. The whole day we were drawing, measuring and filming. We also tested so called ‘coded targets’ which should make the photogrammetry a lot easier. More on this, see below.

Now that we are familiarized with the site and have an overall picture of what is down there we are able to start taking measurements. We do this by selecting datum points which allow us to work in a precise way. These points correspond to different features or locations of the site. The measurements are made by using a method called triangulation. Measurements are taken between three different points, they are recorded underwater and once the diver brings them up to the surface they are entered into a computer program called Site Recorder. Site Recorder immediately tells you if you measured correctly and what the margin of error is. With all of these measurements we gather we are then able to draw an ever more accurate site plan and they can be used alongside the photogrammetry software.

Entering the measurements in Site Recorder
Entering the measurements in Site Recorder

For the OVM 10 we are trying out coded targets. These coded targets are attached to wood and/or are placed between different objects on the site. The coded targets are necessary for this site as recognition points because the site is spread out over a large area, with frames and deck beams surfacing the seabed.Between areas of sediment there are few features to detect. After stills are taken from the GoPro footage, Photoscan software can detect the coded targets in these photos more easily and align them much faster.

Lots of activity on deck
Lots of activity on deck

Three days ago we started off with a rough sketch of the site. Already we have a much better understanding of what is left on the Oostvoornse lake bed. With the actual measurements of the ship elements and their spread, step by step we are geting a good idea of what is there and what the significance is of OVM 10. The filming underwater is harder to do than on OVM 12 because of the spread of the elements and the visibility that is less here. This is why – as a backup – we will also use the conventional methods to record the site with additional drawing.

A coded target that is placed on the site
A coded target that is placed on the site

A large spread, interesting features, lots of illegal excavation done and wood exposed recently. What can we say about the condition of the site? More about that tomorrow.

Robert de Hoop (intern Maritime Programme)

Over Maritiem Programma

Het Maritiem Programma van de Rijksdienst voor het Cultureel Erfgoed houdt zich bezig met het onderzoek naar scheepswrakken, bruggen, havens en andere maritieme landschappen. Het doel is om kennis, onderzoek, beleid, samenwerking en educatie op het gebied van maritiem erfgoed in Nederland een stevige basis te geven. Het programma loopt van 2012 tot en met 2015.

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