ArcUser
Spring 2012 Edition
Photogrammetric Modeling + GIS
Better methods for working with mesh data
By Rachel Opitz, University of Arkansas, and Jessica Nowlin, Brown University
The method of bringing photogrammetric data into a GIS to create simple visualizations described in this article is being used in ongoing University of Michigan excavations at Gabii, Italy.
This article as a PDF.
The authors describe how to bring photogrammetrically derived meshes into a GIS so that the 3D relationships between features can be easily understood, descriptive data can be integrated, and spatial analysis tools in GIS can support analysis and interpretation after the field project has ended.
Photogrammetric Survey in Archaeology
Close-range photogrammetric survey is increasingly popular as a recording method in archaeology. Photogrammetric survey uses a series of photographs of an object to deduce and accurately model its geometry.
This technique is commonly used to document features with complex geometries or large numbers of inclusions, including walls, pavements, rubble collapse, and architectural elements. These types of features can be quite time-consuming to document thoroughly by hand or using conventional surveying in the field.
The use of photogrammetric recording can greatly benefit projects by saving time and creating a visually rich final product. Photogrammetric models might be used in excavation to record a complex sequence of walls or a tomb or on a survey to document the environment around a rock art panel.
A textured mesh of a typical archaeological feature, a pile of rubble, viewed in Meshlab
Photogrammetric models are typically assembled and processed in specialized software including PhotoModeler Scanner, Autodesk's 123D Catch, and Agisoft's PhotoScan. Information on photogrammetric modeling is available from these companies.
A typical final product from a photogrammetry project is a textured polygonal mesh combining color and geometry data. In archaeology, the geometry of the features recorded is often complex, and both the position and shape of these features are important, so keeping the data in a mesh format—designed to handle complex geometries—is desirable rather than converting to a simpler geometry type or a voxel model. [Voxel models use elements that represent a value on a regular grid in three-dimensional space.]
Looking at these models on their own can be useful, but to really exploit their potential, they should be viewed in context along with other data, such as survey data, photos, descriptions, and models of adjacent features that are collected in the course of a project.
Working in Meshlab, unwanted polygon faces are selected and deleted.
Why Manage Photogrammetric Models in ArcGIS?
Many excavations already use ArcGIS to manage their spatial data and maintain links with other relational databases containing information such as stratigraphy, environmental data, ceramics, and osteology. Managing the results of photogrammetric surveys within an existing GIS environment is a practical solution to the problems of organizing, visualizing, and creating documentation from the 3D models. Bringing the models into a GIS facilitates the integration of photogrammetric and conventional survey data, making it easy to place the photogrammetric models in their proper locations. Finally, storing the models in ArcGIS allows archaeologists and managers to continue to work in a familiar software environment.
The Basic Process
Much of the work required to bring photogrammetrically derived meshes into a GIS involves the production of a clean mesh. Once this is achieved, importing the mesh into the GIS is straightforward using the tools pro