Taking 3D Scans at the 2018 Digital Heritage Conference
In July of last year, Paul Veisze, California Department of Parks and Recreation’s Geographical Information Officer, invited me to participate in the 2018 Digital Heritage Conference during the weekend of October 26. He was interested in continuing a project that I had started when I first began working here at CSDS – in fact, it was my first experience with 3D scans.
Back in August of 2015, I’d scanned the entirety of Sutter’s Fort: interior and exterior. It resulted in a total of 156 3D scans and a point cloud of over 1 billion points. This provided them with a highly precise deliverable that they could use and archive for a range of purposes including maintenance, recordation, preservation, and creating other deliverables such as walk-throughs for ADA access.
However, the fort was under construction for restoration and maintenance at the time. The courtyard was excavated in some places and there were stockpiles of dirt in others. The rooms of the fort were also in various orders of disarray and not set up for exhibit due to the construction. Additionally, we did not set the project up on any sort of geospatial control network, which ultimately meant that we had this tremendous amount of very precise data that wasn’t tied to any actual locations.
The scope of this current project was to see if we could merge the additional point cloud data that we had collected from July to September into the larger point cloud that we created in 2015. Additionally, we wanted to put it onto State Plane Coordinates. We decided to focus on the central building of the fort.
First, we set some control points using the CSDS VSN. That allowed us to then set up our 3D scans on those points and have all of new scans be on the California State Plane Coordinate system. We established a small control network around the central building where we would be taking most of our measurements and collecting our data. That way, when we merged the new 3D scans with the older ones, the whole point cloud would be georeferenced.
Next, we scanned around the outside of the central building. This captured not only the central building, but most of the courtyard within the walls of the fort. This was very helpful, as the original data showed the courtyard under construction. The more recent 3D scans included the courtyard as it was intended for the public.
I then merged the new SX10 scan data with the original 2015 scans. The result was a combined point cloud with a residual error of less than 0.010 sq ft.
Afterwards, we used the S7 robotic total station to traverse through the central building where we used the direct reflex (DR) function to lay points on the walls for hanging checkerboard targets. These were used as tie points for the following phase of the project, which was to scan the inside of the central building using the GeoSLAM Zeb Revo mobile handheld scanner and then merge the interior point cloud to the exterior cloud. While the limitations of the Zeb Revo made it impossible to use the tie points, I was still able to merge the point clouds using a simple cloud to cloud registration function in Trimble Business Center.
Ultimately, we were able to merge all of the point cloud data together to create a precise 3D digital database of the historic property that consists of over one billion points and can now be referenced and used by multiple divisions within State Parks to create products for public access and outreach, creating as-built models for maintenance and preservation as well as a 3D record that can be added to and layered over time.
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