Origin Point, Inc. Computer Photo and Video Perspective Analysis

The need for a dimensional tool
In most cases, it is impossible to thoroughly document spatial data during the course of a post-fire investigation. This is due to time constraints, the inability to physically access potentially dangerous areas or the lack of foresight to record all measurements. It is also nearly impossible to derive accurate area calculations of irregular shapes, such as burn patterns, through the use of conventional methods. Furthermore, as the case develops, it is often too late to return to the fire site to confirm previous observations. In response to these problems, Computer Photo Perspective Analysis (CPPA) was developed in order to derive spatial data from on-site photographic and video documentation.

Data input requirements for CPPA
CPPA works in conjunction with two important elements: good on site documentation representing pertinent objects and areas of interest, and an accurate computer 3D reconstruction of the building structure.

Overview of the CPPA process
To better understand the CPPA process, an example of this methodology is used and pertains to the recent analysis of a fire that occurred at the Ryan Fun & Fitness Center in West Burlington, Iowa. The following describes the development of a computer perspective match and the area calculation of floor burn patterns in the Nautilus room inside the Ryan Fun & Fitness Center.

Projection of Computer 3d reconstruction model
A post fire photograph of the Nautilus room showing the floor burn patterns is digitized into a computer image file using a flatbed scanner. The computer image file is then loaded into 3d StudioMAX (3D modeling and animation software) as a background image.

3d Studio MAX has the ability to generate a virtual camera that can simulate that of a real world camera. This camera can be placed anywhere within the computer generated environment of the fitness center. Figure 1 illustrates the virtual camera looking South into the Nautilus room.

A view port on the computer monitor represents what the virtual camera sees and is similar to looking through a camera viewfinder. This view port displays the post fire photograph as a background image. As shown in Figure 2, a wire-frame representation of the 3D model geometry is concurrently projected onto the background image. The wire-frame represents key elements in the Nautilus room, such as the floor perimeter, walls, and structural steel.

Alignment Process
The alignment process begins by placing the virtual camera and its target (center of view) at the approximate location of their real world counterpart. It should be noted that AutoCad and 3d Studio MAX are dimensionally accurate and they relate to real world dimension units such as feet, inches, meters, and centimeters.

The alignment process continues by refining the camera placement and other camera parameters including lens focal length (field of view) and roll (tilt), until there is a direct visible correlation between similar key elements in the background image and in the projected wire-frame.

Mapping Process
Once the computer photo perspective match is established, the second step consists of defining a theoretical two-dimensional plane onto which the floor burn patterns in the background image can be traced. A simple analogy would be tracing the forms of distant objects on a window pane. The computer operator uses a pointing device (mouse or digitizing tablet) to outline the burn patterns on the photograph represented in the view port. The outlined objects are simultaneously plotted onto the theoretical two-dimensional plane. This plane is coincident with the virtual floor in the Nautilus room and is shown in Figure 3.

The end result is a series of two-dimensional shapes representing the floor burn patterns which is integral with the existing 3d construction model. Figure 4 shows the floor burn patterns in relationship to the contents in the Nautilus room. If three-dimensional data is required of the object or area of interest in the background image, then the second step in this process is repeated with the theoretical two-dimensional plane defined on an alternate axis.

Area Calculation
The 2d shapes representing the floor burn patterns are considered to be valid geometry by both AutoCAD and 3d Studio MAX (r2). After a simple query is made, either program calculates the area. Figure 5 presents a plan view of the floor burn patterns and the burn pattern area in the Nautilus room.