Theatre Design & Technology - Fall 2020 - 43

coffee table form the center pieces to a
room surrounded by contemporary furniture and decor. Four doorways provide
pathways to the wings, while a larger entryway to a patio sits upstage and raised
by three steps. This layout proved a perfect subject to test photogrammetry for
set design documentation.
The set was photographed from various angles using a Canon EOS Rebel T3,
capturing images at 12.2 Megapixels. A
total of 518 photographs were taken-a
process that took approximately 50 minutes to complete. Collecting the images
requires a thorough progression, making sure to photograph the object from
every angle possible while keeping an
overlap between photos (Image 1). This
last detail is critical for later alignment in
the software, and it is recommended that
at least 60 percent of every photo overlaps the previous (Korumaz, et al. 2014).
Lighting is an important aspect to consider at this stage. Lights can be set to a specific cue to incorporate the mood of the
show; however, full lighting allows for the
best likelihood that all aspects of the set
will be visible in photographs and, therefore, preferable for digital reconstruction.
These images were then transferred to
a computer and inserted into a software
program, Agisoft Metashape Pro.
This Structure from Motion (SfM)
software aligns the photos by finding
common points within the images, recognizing the spatial relationship between
each photograph. Inherently, this necessitates a powerful computer to properly
process the images and resulting point
clouds. For this model, a desktop computer with 32 GB of RAM and a 3.60
GHz processer was used. While more
than efficient for everyday tasks, each
step in the photogrammetric process
still required several hours to complete.
The complete process includes aligning
the photographs, creating a dense point
cloud, then a mesh model, and finally
adding texture from the images. At each
stage, one can select the level of accuracy,
with the choice of a longer process time
but the likelihood of a more complete
result. For photograph alignment, choosing the " Highest " accuracy setting meant
waiting more than five hours for completion. For comparison purposes, the result
was saved, and the photographs were realigned under a " Medium " accuracy (taking 75 minutes). The resulting product

From top to bottom: Image 2: Initial Sparse Point Cloud; Image 3: Optimized Sparse Point Cloud;
Image 4: Initial Dense Point Cloud

was not noticeably different, and therefore the following steps were completed
in " Medium " accuracy unless the outcome was unacceptable for any reason.
Once aligned, Metashape creates a
Sparse Point Cloud of the points in the
model most identified throughout the
images (Image 2). Next, the points with
a low percentage of accuracy and uncertainty must be eliminated. This keeps
the software focused on the best points
it recognized, and from these the rest of
the model is constructed. This process
lowered the points in the Sparse Cloud
from 447,000 to 52,000 (Image 3). It is
also best at this time to optimize the camera locations to fine tune the alignment
towards these points of focus. Next, a
Dense Point Cloud is assembled which is

the lengthiest step in the entire process,
taking more than four hours and creating 14 million points (Image 4). The next
step is to create a mesh. This mesh is the
skeleton of the model, and it is formed
by connecting these points. Therefore,
prior to building the mesh, it's important
to ensure flat surfaces are smooth and errant points are eliminated. Much of these
points are superfluous to the set and are
taken out, reducing the total here to 11.6
million and taking less than a half an
hour to complete (Image 5).
With the Dense Point Cloud
trimmed, a mesh is built. The mesh is
constructed of edges, vertices, and faces.
An important aspect to consider is the file
size of the model once completed. The
smaller the file, the quicker and easier
FALL 2020 | THEATRE DESIGN & TECHNOLOGY

| 43

Theatre Design & Technology - Fall 2020

Table of Contents for the Digital Edition of Theatre Design & Technology - Fall 2020