GIRI originally was conceived when strange but ubiquitous two-dimensional fossil forms were found in approximately 640 million year old stromatolite reefs from the Trezona Formation in South Australia. The forms were thought to be part of larger three-dimensional objects, but could not be imaged via X-ray computed tomography scanning techniques due to the very weak density contrasts (both the fossils and matrix are made of calcite). Manual serial grinding and imaging of these Trezona objects led to the 3D reconstruction of sponge-like organisms suggested to be the oldest body fossil record of animals.
Above, floorplan of the Princeton Grinder Lab.
Above, The Grinder Room showing GIRI and a variety of support equipment.
Central to the Princeton Grinder lab is GIRI, the Grinding, Imaging and Reconstruction Instrument, which was designed and built to generate 3D digital models of objects embedded in materials such as rock and metal. The instrument works by employing an automated routine of serial sectioning and imaging. Sectioning is accomplished by a precision CNC grinder. An integrated 80 megapixel camera acquires images with high precision registration and 48 bit color depth. This process destroys the sample while creating a permanent digital archive of serial images. Automated routines using color and textural vision algorithms isolate complex structures and objects. Hundreds of these segmented slices are combined to create 3D mathematical models. Quantities such as porosity and permeability can be computed directly from the models. Models can also be used for hydrodynamic simulation, morphological analysis, and a variety of other computational simulations. GIRI excels at identifying embedded objects with weak density contrasts that might otherwise be invisible to X-ray CT scanning methods. GIRI can process exceptionally large samples (20,000 cm3) with heterogenous characteristics.