Our class has been assigned with laser scanning tabby remains on the coastal island, Sapelo. The scanner we used was a Faro Focus scanner, which uses wavelengths to read data. It can also capture color data through a camera to add textures to any scans. On board power, storage, and interface allows easy use. The Faro Focus is a medium range scanner, which makes it ideal for capturing building exteriors. Things to consider when scanning on site:
- How much data needs to be collected?
- What resolution should it be in?
- How much time needs to be spent on site?
When laser scanner, quarter resolution is perhaps the best resolution to begin scanning in exterior conditions. This equates to each scan taking about 10 minutes to capture around 40 million points of data.
The class began working with the Faro Focus scanner in class on May 8, with a demonstration of how to begin operating the software and scanner. We completed preview scans of the lab in the Clarence Thomas Center (CTC).
The site in which the class will be laser scanning is Sapelo Island, located sixty miles south of Savannah, Georgia. As the fourth largest island in the state, Sapelo is state owned and managed. Resources located there include the African American community of Hog Hammock, the University of Georgia Marine Institute, the Richard J. Reynolds Wildlife Management Area, and the Sapelo Island National Estuarine Research Reserve.
Settlement began some 4,500 years ago, with Native American settlements located throughout the island. A Native American Shell Ring (prehistoric mound for ceremonies) is located at the north end. Spanish colonists landed in the area between 1573 and 1686. The English began their colonization following James Oglethorpe’s settling of Savannah just north in 1733. Over its history, the island became a place of agriculture, timbering, and livestock raising. It was in the beginning of the 19th century that the plantation economy reached the shores of Sapelo, with Thomas Spalding industrializing the island by erecting a sugar mill, lighthouse, and tabby structures. This complex became an extensive antebellum plantation.
The African American settlements on the island are historically significant. During its industrial planting years, Sapelo was home to 385 slaves belonging to the Spalding family. Following the Civil War, the freed slaves remained on the island, eventually purchasing their own lots to create communities, like Hog Hammock. African American residents played a massive role in the agriculture, timber, and oyster economies on the island.
In the 20th century, the island survived many changes, including the rebuilding of Spalding’s original tabby mansion (ca. 1810), the expansion of the planting, milling, and seafood industries, and the installations of roads and wells. In 1934, Richard J. Reynolds Jr. purchased the island, eventually combining the African American communities into one (Hog Hammock) and creating the Sapelo Island Research Foundation.
Today, many of the 115 residents are descendants of Spalding’s slaves. The traditional Geechee culture of the region is slowly diminishing and is becoming a concern for historians, preservationists, and local residents.
Information for this history was provided by www.georgiaencyclopedia.org.
Meeting on Wednesday, May 10, 2017, the class began the scanning process. After taking the ferry to Sapelo Island at 8:30, we were driven by JD, an employee, through dense trees to our scanning location. Our focus was directed towards scanning one of the buildings of the Chocolate Plantation on the north end of the island. The area consists of close to a dozen tabby ruins spread around a reconstructed tabby barn. In the intense heat, we began the process by taking field notes, drawings, and photographs of the various buildings on the property. In all, there were around 13 ruins that were clearly visible to us. I sketched the location of each ruin to ensure proper documentation of the surrounding area. The ruins were beautiful.
After sketching and photographing the ruins, professor agreed with us that one of the ruins that was completely open in the field was the best option for the first laser scanning. The other students were brought in to the ruins and we plotted where exactly we would place the laser scanner to ensure proper data capturing. The tabby ruin, of what appears to be a slave cabin, was comprised of thick walls and an interior wall, dividing the space into two. I planned that we would place the Faro Focus scanner at each exterior corner and inside each room to ensure we fully captured the exterior and interior. At around 10:30, the scanning process began. The first scan, with the scanner on the tripod, was a 360 degree preview scan of the southwest corner. A preview scan, which took 4.5 minutes, was necessary to ensure we captured the building. We selected Parameters – Preview – Home – Start to preview scan.
As the preview completely captures a 360 degree scan, it was necessary for us to zoom in on the building only to reduce time and to only capture the building itself. In order to do so, we selected Parameters – Horizontal/Vertical – and zoomed to the building to only capture a certain area. Once completed, we set up an official first scan. To do that, we selected Parameters – Resolution – 1/4 – Outdoor 20. These options allowed for a 10 minute scan to capture around 40 million points of data. This preview and scan process was completed for each of the corners of the buildings.
As for the interior space, we decided to reduce the resolution to save time. It was also a small enough space that such a high resolution as 1/4 was not necessary. Since we were capturing the room in 360, we only needed to complete an actual scan as we did not need to zoom in on a certain area. Using the steps for actual scans, we changed the resolution to 1/5. This reduced the scan time from 10 minutes to 6 minutes, only capturing around 27 million points. This process was repeated for the second interior room. Once those scans were completed around 11:30, our job on Sapelo was done and we returned to the ferry.
To begin the registration process, we copied the file with the scans from Professor’s USB drive to each computer in the CTC lab. Once the file (workspace.fws) was automatically transferred into the Faro SCENE program, they were saved into a local workspace (folder) onto the desktop titled, “Chocolate Plantation.” With the scans open in SCENE, each was assigned a name, such as CP_001, for Chocolate Plantation_scan number.
The first step in the registration was to remove the preview scans. Knowing that we took a preview scan before each scan, save the last two, I selected every other scan and made sure it was a preview scan (was 360 degrees of data). Right clicking on the scan name on the left hand side allows for the scan to be deleted. Once the previews were deleted, we were left with scans CP_002, CP_004, CP_006, CP_008, CP_009, and CP_010.
Next, color must be added to the scans. To do so, right click each scan on the left hand side of the program, select Operations – Color Pictures – Apply Pictures. This applies the color photographs that the laser scan took while scanning the ruins. To bring color to each of the scans, complete the same process for each. Along the top tool bar, there is a tab named “Gexcel.” By selecting this, it exports the scans into JRC Reconstructor, which is a better program for registering the data than SCENE. When exporting the scans to JRC, make sure to select all of the scans, select the color option, and leave the setting for export 1 out of every 1 point of data (this ensures no data is lost).
During the exporting process, RGP files and folders are then created. A separate folder was created to house these files and folders for working with, labeled “Reconstructor” in a larger folder for the class project. The exporting process also creates a JRC Reconstructor file, which needs to be opened to begin the registration process. Again, along the left hand side, all of the scans are organized by name. The work space in JRC is completely empty, as each scan must be loaded into the space. To do so, right click on the desired scan and select Load Model. The model should then appear. Multiple scans can be loaded into the work space simultaneously. The next step in the registration process involves bringing the color back into the scans. By selecting an individual scan, the property browser (lower left corner) provides a selection Color Mapped. Make sure to select color to change the data in the scan to colored.
Next, the scans must be processed. To do so, select all of the scans on the left hand side and select Line Up – Process- and then remove the selection for Auto Registration and Fine Registration (this ensures that any data alignment is done manually). Clicking Process will process the data of the scans. Once completed, the scans will have to be reloaded into the workspace for viewing.
From this point on in JRC Reconstructor, there is no undo option, so ensure that everything done is done correctly in order to reduce error. The next step is to remove excess data aside from the ruins. To easily complete this, using the mouse to view each scan from above. In the top right hand corner of the tool bar is a Selection Tool. Drawing a rectangle around the building and then selecting Delete Outside will delete any scanned objects around the selected ruins. Complete this process for each of the scans. Now begins the aligning of the various scans.
Referencing field notes, select two scans that have overlap for easy alignment. The alignment process is very similar to that of the Artec and NextEngine software. For the tabby ruins, I began with scans CP_002 and CP_008. By selecting the two scans on the left hand side, I selected the Registration tool in the tool bar and selected Manual Preregistration. A pop up window will be opened for the special registration process. In the lower right corner, the two selected scans will be presented. Choose one as a reference scan (what the other scan will be align to) and the moving scan (the scan that will be moved to be aligned to the other). This will reveal the scans in a black and white window above. The color can be presented by selecting the Reflectance drop down and choosing color. Like the other laser scan software, registration involves placing three points on corresponding points on each scan. Using only the mouse wheel to zoom in and out, double click on any points on each scan to select a point. The program requires at least three points. Make sure to select points that are in the data cloud (or on the actual object) and not in the black space or else it will be invalid and will not properly register. Once three points are selected, click Commute to align the scans. A message will then pop up and present the error size for the registration. An acceptable error is under 0.5. The first error I received for aligning CP_002 and CP_008 was 0.030673. This was great and so I clicked Apply. The scans were preregistered and aligned together. This process must be repeated for each consecutive scan. Make sure to select one of the previously registered scans for the next registration. For the next process, I selected CP_008 and CP_006 to align. This will ensure that the CP_006 scan will then be aligned with CP_002 and CP_008 scans that were just aligned. However, after the first scan, careful consideration must be paid to which scan is selected as the reference scan. Since it has already been aligned, the previous scan (CP_008) was selected. The error for that alignment was 0.067780.
The next scans that were aligned were CP_004 and CP_006, with CP_006 as the reference scan. The error was 0.051578. Following, CP_010 and CP_002 were aligned, with CP_002 as the reference with an error of 0.035620. Finally, scans CP_009 and CP_010 were registered together with CP_010 as the reference.
I had some difficulty with the first few attempts at selecting points on each scan. Some of the points where too close to the edge and therefore the error was higher. I found that selecting the origin and other points about mid-way up the tabby walls resulted in the least amount of error. The interior scans also proved to be the most difficult to align together (CP_009 and CP_010). These scans had little recognizable points to select to align. After zooming in fairly close, I was able to distinguish subtle differences and align it perfectly.
Back in the workspace, all of the scans were reloaded and were successfully aligned together. To refine the alignment and reduce error, select Cloud to Cloud Registration. This will further refine the registration of each scans and fix any mistakes that may have previously occurred. This process is very simple. Selecting the same scan combinations as the preregistration on the left side of the window, (i.e. CP_002 and CP_008), simply click Process. The pop up window will display the program completing the refinement process. Another error window will be presented. If satisfied with the margin of error, select Apply. Once clicked, the refinement is finished. Repeat the process for the same scan pairs that were selected for preregistration.
The final steps of registration involved combining all of the scan clouds of data into one single point cloud. In order to do so, select all of the scans on the left panel and right click on them. Select Filtering & Clustering – Make Single Cloud. The new cloud will appear under a new section titled “Unstructured Point Clouds.” I made sure to load the “chocolate cluster” model and turned on the color to see the point cloud. The next step involves creating a Universal Coordinate System (UCS) that orients the model to an XYZ grid so that it can easily be uploaded into Revit or AutoCAD and be oriented correctly. Click the Cross Sections tool in the overhead tool bar, and select Edit Plane. A pop up window will appear on the right hand side. This window will allow you to select an origin point (X) and two other points on other axes (Y and Z) to orient the model. To select a point, hold down ALT and double click on a point. We selected a corner of the ruin as the origin. Once the origin is selected, select two other points on other axes. Once completed, select Create/Edit from Specified Points. This will create a grey opaque plane that rests beneath your model. Ensure that it is perfectly horizontal by selecting Make Plane Horizontal. This levels the plane. Shifting focus to the left hand panel of scans and models, select the new plane under the Planes Section. Right click on the new plane and select Create UCS from this pose. Locate the new UCS model and set it as current. The goal of this step is to ensure that the walls of the model are parallel to the XYZ lines of the coordinate system. For this model, the longer wall aligned well with the Y (green) axis, and the shorter wall with the X (red) axis.
This process was tricky, as it was very difficult to try to get the longest walls aligned with the axis. Twice, I deleted the previous selected points and axis to redo the process for better results. After the third attempt, the results were really great and so I saved the file.
This process is necessary as it enables the model to be plotted according to axes that are consistent through Revit or AutoCAD, allowing easy detailed drawings or elevations to be drawn from scale.
The final step is to export the model. Right click on the single cloud, “Chocolate cluster” in this case and select Export model as… Select an e57 file. Make sure to select Export Position in Current UCS and to change the color from Range to Color. This ensures the model is exported oriented to the XYZ axes and that it retains its color.
Once exported, the e57 file (287 mb) was opened in Autodesk ReCap 360 and saved as a .rcp file.
In the hopes of importing this model in Sketchfab, we selected the Mesh Tools – 3D Mesh option on the overhead tool bar. A pop up window opens and select the cluster (“chocolate cluster.”) Another pop up window opens. Make sure to change the color output from Range to Color. Select the output triangles as Average. This will only create enough faces that it will not exceed the file size limit for Sketchfab. After a few minutes of waiting, a 3D mesh file was created. Under the Triangle Meshes section on the left hand side in JRC Reconstructor, right click and select Export model as… Select the file types as a .ply (polygon mesh). A pop up window will be presented. To export the desired properties, select Export Color and Export Normals. Save it to a desired location. This file will then be able to be uploaded into Sketchfab for viewing. The class had trouble figuring out what file format was optimal for uploading the model into Sketchfab.
Overall, the 3D mesh removed quite a bit of detail and removed the rugged texture of the tabby ruins. But the model looks great and offers a great platform for viewing the comprehensive reconstruction.
The scanning process and JRC Reconstructor software were both much easier than was expected. The software allows for easy to find tools and processes that are not too confusing for first-time users. And I am beyond happy with the final results.