In 2012 I prepared documentation of the masonry surfaces of this historic room in the Maryland Statehouse. This documentation provided a baseline of the existing conditions to allow for an investigation into how exactly the room was appointed in its heyday – when Thomas Jefferson was named ambassador to France etc…
The documentation that I created consisted of measured line drawings (in CAD format) augmented by a mosaic of photographs that had been rectified to match the real world size and shape of the various portions of masonry. here is what it looked like:
The image above ^ shows a screen capture of an accurate measured line drawing delineating the limits of the masonry surfaces and indicating the architectural features nearby.
This image ^ shows a drawing layer “thawed” to display a sort of key plan to the different regions of masonry for which individual rectified photographs were prepared. The next few images show some of the drawing layers containing these rectified photographs “thawed” and you can get an idea of how the composite whole is constructed like a mosaic.
So, the above image ^ shows how the entire wall could be captured, rectified, and brought into the measured drawing. (The reason that the other images were created in “panels” was to provide for two things: (1) enhanced resolution for the individual photographs, and (2) the ability to “see around” obstacles presented to a single point of view. For example, in the image above, portions of the masonry surface are obscured by some of the architectural detailing/millwork)
Below is a “zoomed in” version showing this condition in higher detail…
So, in this approach, the line drawings carried the responsibility of delineating the wall’s size, shape and configuration of architectural elements while the rectified photos carried the responsibility of conveying the lay out and character of the masonry construction units.
Today, I might approach the project differently, using a true “Orthophoto” of the sucrose instead of a mosaic. The distinction is important. An Orthophoto is a planar projection of a dense point cloud or textured mesh 3D model. I was unable to create these back in 2012 when I did this work – but today I can do so -still using photogrammetry- and maintain the same level of accuracy demanded by such work.
This image ^ shows the orthophoto seated nicely behind the measured line drawings. As mentioned above, it is a projection from a 3D model, which can be looked at from a variety of angles and manipulated in 3D modeling software . below is a video clip showing the model these surfaces.
I am really excited to have this new set of tools at my disposal! The mosaic approach is still sound and may be more appropriate for some projects. In fact, the two approaches can coexist in the same set of documentation if needed. But the addition of 3D scanning and the creation of true Orthophotos to my toolbag will allow me to provide architects and engineers faced with complex preservation challenges with more options.
more background info here: