As mentioned previously, this project was delayed into the summer semester due to COVID-19. The face-to-face portion of this internship hinged on meeting together with Dr. Walters, Dr. Michlowitz, and Dr. French at Piney Croft to scan the building using the Lecia RT360 terrestrial laser scanner. Working around some weather delays we were all able to convene on Monday, July 28th to scan the residence early in the morning to avoid the Florida heat.
My site
map that I constructed at the end of the spring semester was not used to direct
the location of the scanner, for that we used Dr. Walter’s on the ground direction
to ensure the best scan. Instead, what my site map allowed me to do was to
compare the scans we took and problems we encountered to what I surveyed a few
months prior. Overall, we took roughly
30 scans of the building’s exterior which is very similar to the number of
scans on my site map and the probable difficulties I encountered turned out to
be the exact difficulties we encountered later on.
Vegetation
was the largest concern since a few trees and bushes grew close to the
residence at the front of the house as well as near the rear of the A-frame
structure and other than scanning behind the bushes, there is not much that
could be done to scan the obscured portions. One concern I did not foresee came
from scanning the house at a distance, since this is a residential area, we could
not traipse through neighbors’ yards for the sake of unobscured data that could
only be viewed from far away. While these two difficulties presented concerns
for the final product, not much could be done, however, this illuminated the
limitations present in the field that the articles I read previously in the
spring semester echoed. Barring expensive scaffolding and roof access to other
buildings, these limitations just have to be accepted and this project gave me
a greater appreciation and understanding with these present limitations of terrestrial
laser scanning.
The
scanning process itself was not too difficult, the scanner is easy to move
around and is connected to an iPad that is running an app that allows us to
start the scanner remotely and monitor each scan and link them to one another all
while in the field. We enabled the Lecia RT360 to take photos in addition to
each scan in order to get color mapped onto the point cloud, while it raises the
overall scan time to about 1 minute and 15 seconds, it is still much faster
than the older Faro terrestrial laser scanner which takes approximately 15
minutes for scans.
I was surprised
on how easy the process was, trying to replicate the work done with
photogrammetry definitely would have been very time-consuming and nowhere near
as accurate. The drawback to the laser scanner is its obscenely high cost. The
Lecia RT360 costs approximately $80,000 with a proprietary $750 USB stick, when
contrasted with low-cost photogrammetry the difference is astounding. This
difference will be evaluated later in the internship by comparing the laser-scanned point cloud to that of a photogrammetric point cloud.
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