Structure From Motion
Overview
The goal of this project was to create an accurate, 3D model (known as a structure from motion model) of a feature, structure, or object in Laurel Grove Cemetery. The chosen object had to be of a manageable scale so that photos could be taken from every angle. Photos would be taken ( a minimum of 20) with a DSLR from multiple angles of structure and object within the cemetery. These photos had to be clear and in focus as poor lighting or out of focus elements could make later stages of rendering more difficult.
After the photos were taken they were grouped together and uploaded to Autodesk Recap. A minimum of twenty had to be chosen for the program to render a model. Due to the complexity of the object chosen 64 photos were used. Autodesk Recap then processed the photographs into a source from motion model. Afterwards, several hours were spent cleaning and cropping the model.
First Phase: Photographing
This included filling holes, smoothing certain areas, and cropping out unnecessary information. Afterwards a complete, clean model was uploaded to Sketchfab. Through this project the process of photogrammetry, how Autodesk Recap works, and how to clean source from motion models was learned.
The site of photographed object was Laurel Grove North Cemetery, located on 802 W. Anderson St, Savannah, Georgia. The cemetery was developed in 1850 after several other local cemeteries reached capacity. The north half of the cemetery was reserved for white whereas the southern half was for African-Americans.¹ Today the two sides of the cemetery are divided by Highway 204. The northern half of Laurel Grove Cemetery is home to a number of Victorian-era monuments as evidenced by the architecture of some mausoleums and monuments.
The process of investigating the site first began before even visiting the site in person. A precursory survey of the site was done using Google Maps to find places of interest before going to the site. Several locations were kept in mind and helped to narrow down what type of objects were going to be photographed.
Photographing of the site began on April 4th at 11:00 AM and ended at around 1:20 PM. Multiple objects were photographed however the primary object of interest was a human scale angel sculpture found on the west side of the site. Photos were taken from a low angle at first in order to capture the detail of the drapery and the base. Photos were taken from all angles at a low, medium, and high height. The medium height was from normal standing height and the high height was from an elevated angle, looking down on the statue to capture the detail in the hair and the wings. Additional photos were taken to photograph the facial details as well, form the sides and from below the face.
Photographs of the marker used to create the model
Second Phase: Autodesk Recap
After the photos were collected and organized they were put into Autodesk Recap. This step of the process did not require a lot of interaction as the process was automated. The programs simply required a minimum of twenty photos which were then uploaded to the Autodesk cloud and processed serve side. This processing took roughly four hours due to the large number of photos used. Several other objects were also processed as additional models. These additional objects had less photos and as a result were less detailed or had holes in the model which were too large to fill accurately.
Cleaning up the model in Autodesk Recap
Third Phase: Cleanup
Once the models were processed they could be viewed in Autodesk’s model viewer. The first thing that was noticed was that the process attempted to model elements of background features in the distance. This resulted in a messy environment surrounding the primary object. Many of these background features had holes or stretched textures that looked incomplete. Fortunately, the program allows users to use a selection tool to crop out unnecessary elements. The unfinished surrounding elements were cropped out. This eventually resulted in the model consisting solely of the angel sculpture.
Additional cropping was done to further reduce background noise. Cropping was also done around the base of the statue because the holes left behind were too big to fill. A significant portion of the sculpture’s base being removed cause a hole to appear around where the knee of the sculpture is. To fix this the fill tool was used to create a smooth cap to the hole. From there surface sculpting tools were used to push the cap to make it less noticeable. Afterwards it was smoothed with a smoothing tool to have it blend to the rest of the sculpture. Unfortunately, there was a somewhat noticeable difference in the texture of the cap and the rest of the sculpture but it fit with the rest of the sculpture in form.
A final cap was placed on the bottom of the sculpture for the purpose of later 3D printing. This process required the cropping of the base and close cropping around the feet of the statue. A lasso crop tool was used at a close zoom to crop it as cleanly as possible. After the unnecessary parts of the statue’s base were removed the fill tool was used to place a smooth, untextured cap at the bottom of the statue. The model was now ready to be uploaded and formatted for 3D printing purposes at a later date.
From here, the model was exported and decimated (reduced in file size) so that it could be uploaded to Sketchfab or other online databases. Once uploaded to sketchfab properly lighting and environmental settings were set up so that the sculpture could be viewed properly.
Fourth Phase: Printing
The final phase of this project was the process of 3D printing. This was done using the printing laboratory at Fahm Hall. An .obj file of the cleaned up model was brought to the printing lab at Fahm to be looked at by the technicians there. After processing how it would sit on the printing tray and which orientation it should be printed in (horizontally or vertically) it was accepted to be printed. The model was printed on an FDM printer. The printing process takes roughly a day and half. Afterwards, the printed model has to be bathed in a chemical bath. This is done because for the model to stand properly during the printing process it has to be covered in a support material. This support material dissolves in the chemical bath while the model itself does not. After a day of sitting in the chemical bath the 3D printed model was retrieved.
References
1 "Laurel Grove South Cemetery." SavannahGa.gov. https://www.savannahga.gov/882/Laurel-Grove-South-Cemetery
(accessed May 12, 2018).