Scattered around the United Kingdom are a series of defensive bunkers known as pillboxes. Built during much darker times, they serve as reminders of history. Although some have been removed over the years, many still survive. We use photogrammetry digital preservation to document and protect these historical structures for future generations. Most stand empty and unused while a few serve as man-caves or apple stores. One of these bunkers serves as a wine cellar. They make great subjects to digitally preserve with photogrammetry.
These curious structures are not so large it takes thousands of images but always enough to present a challenge somewhere. Any whose entrances remain open are good test for photogrammetry skills as incorporating the internal space always needs thought and care.
Adding Value
A basic 3Dd shape is useful but remains limited use. Scale adds far more value and in Metashape Professional its inclusion should really be considered as a minimum standard to achieve. But, photogrammetry for digital preserve does have its obstacles.
So when you find yourself presented with a subject and camera but no scale bar what can you do?
Whilst out for a bike ride I came across a pillbox built into the side of a bridge and overlooking a canal. The digital camera was in the rucksack but I carried no scale bar.
The solution? the bicycle frame makes a rough and ready scale bar. Its geometry remains fixed and can later constrain the model.
Summary of Photogrammetry Digital Preserve
Including a known object – a bicycle is just one example – in the scene allows us to include scale and add value later. Even if only Metashape Standard is available, you can still start the project. Later, you can hand over the project files for additional processing in the Professional edition. This is something we teach and encourage in the Metashape Standard for Forensics online training course and will build upon in the forthcoming Metashape Professional for Surveying and Forensics course – watch this space for more news.
With the frame measure and points included the model scaled. Next time I’m passing I will take a few real world measurements of the pillbox, just to prove out the process.