Scanning Old Main – A Preliminary Assessment

Site Overview

Old Main is the oldest building on the University of Arkansas campus. Constructed in 1875, it became the first official University building three years after the University’s inception in January of 1872. This redbrick building with a Mansard roof is a beautiful example of 19th century Second Empire style architecture. The south tower has a concave silhouette, while the north tower has an ogee silhouette. On all four sides of the south tower are large round areas designed to be clock faces. These towers were reversed from the original plan so that the "clock tower" would be closer to the city of Fayetteville for better viewing. No clocks were ever installed, however.

In 1970, Old Main became the first structure in Fayetteville to be entered into the National Register of Historic Places. Withstanding three major fires and over 100 years of weathering and erosion, the building is one of the most significant icons associated with the University and the city of Fayetteville today. As an important historic structure and symbol of this community, Old Main was chosen as the subject of the first scanning project detailing a major architectural structure.

The goal of the project was to create a 3D model of this historic building for publication on the Internet and to maintain a model from which accurate measurements can be derived. The equipment used for the study include an Optech Intelligent Laser Ranging Imaging System (ILRIS 3D), a laptop with the appropriate software, and a digital camera. The scanner has an accuracy of three mm in the x, y, and z directions, a range of 3-350 meters and a data sampling rate of 2000 points per second.

A challenge in acquiring data for the model of Old Main is the large number of trees and bushes that surround the building (see image above). The trees were fairly easy to maneuver around, however this often required positioning the scanner fairly close to the building and tilting it upward. The bushes, on the other hand, tend to be located immediately adjacent to the building and there was not a practical workaround for the acquisition of structural data in these obstructed areas. Scans were acquired in the winter months (leaf-off conditions) in efforts to minimize the vegetation coverage. Because the building is over six stories tall, including the towers, good scan coverage for the top of the building has not yet been acquired. As a result, the towers are still incomplete and the roof is not present in the 3D model.

Old Main was scanned in a series of three trips, each of which lasted 2-3 hours resulting in a total scan time of less than 8 hours. The scans were acquired at a 2-3 cm. resolution. A total of 30 scans were taken from 21 different locations around the building (see image below). The scans took an estimated 4-6 minutes each and the average file size was 10 MB. The data were aligned in PolyWorks fairly quickly and merged into a polygonal mesh with 3 cm resolution.

A standard hole-filling algorithm was run in the IMEdit module of PolyWorks using the following parameters: hole filling distance - .5 meter, edge length – automatic, angle – 85o. The results can be seen in the images below. The remaining holes can be filled in using other hole-filling methods available in the software. However, these methods can be fairly tedious and for the purpose of deriving measurements from the model, hole-filling was not a priority. Therefore, following the standardized hole-filling operation, the data were exported again and imported into the IMInspect module of the PolyWorks suite.

Importing the data into IMInspect
The IMInspect module is used for deriving measurements and other useful information about a scanned structure or object. Before measurements can be extracted from the Old Main model, the structure’s coordinate system was rotated so that it corresponded with the x,y,z axes of the IMInspect viewing window. This means that the front and back of the building would run parallel to the X-axis, the sides of the building would run parallel to the Y-axis, and the Z-axis would correspond with the height of the building. This provides a more realistic viewing perspective of the structure and also makes deriving measurements and fitting primitives a more intuitive process.


To rotate the structure’s current coordinate system to correspond with the viewing window’s x,y,z axes, the “2 planes, 2 axes, 2 center points” option in IMInspect was used. This option allows the user to pick a source and destination plane, axis, and center point about which to translate and rotate the respective object.


First, all of the source primitives were defined by creating and fitting a number of points and vectors to the model. The destination primitives were then defined by creating a new primitive and specifying the desired parameters for that primitive. For example, when creating the destination Z-axis, the orientation parameters specified for the vector were X=0, Y=0, and Z=1. Once all of the source and destination primitives were defined, the coordinate system transformation was applied. In the images below, note the before and after orientation of the structure in the View – Y position.

A simple animation of the Old Main model was created in order to help visualize the entire structure and to emphasize the coordinate system transformation. Note the position of the viewing axes as the structure rotates.

- Old Main animation -


Deriving Measurements using the Basic Measuring Tools in IMInspect

While there are a variety of measurement tools available in IMInspect, among the most basic are the distance, angle, and radius measurement options. This group of measurements is located under the Measure menu in IMInspect. The results obtained from these measurements can be easily displayed in a report which can be exported from the software. Several distance, angle, and radii measurements were made on Old Main. These measurements and the measurement report can be viewed in the images below. All measurements are in meters.

Note that the front of the building is 65.4 meters across and that the sides of the building are an estimated 37.3 meters giving the building a total area of roughly 2,440 meters. Among the most interesting of the measurements is the difference in height between the northern and southern towers. The northern tower, aside from being different in shape and design from the southern tower, is also significantly taller (an estimated 2.8 meters taller).

This report is a preliminary assessment of the initial stages of developing and processing a 3D model of Old Main. Further scans will be conducted on Old Main to obtain more detailed information of the top portion of the building, including the roof and towers. The complete dataset will undergo more complex analysis, using some of the more advanced measuring options. These include the fitting of model primitives and the extraction and exportation of CAD data. Results from these processes will be made available online upon project completion.