An Introduction to Building 3D Crime Scene Models Using Sketchup

ARTICLE Original Article An Introduction to Building 3D Crime Scene Models Using SketchUp Elissa St. Clair1, Andy Maloney2, and Albert Schade III3 1 Naval Criminal Investigative Service, 2 FORident Software, 3 Berks County District Attorney’s Office, Forensic Services Unit ABSTRACT ARTICLE INFORMATION Crime scene investigators generally have two options when they need to create a three-dimensional (3D) Received: 11 May 2012 model of a crime scene: enlist the services of an expert 3D modeller who specializes in graphic modelling or Revised: 20 July 2012 learn one of the full-fledged modelling tools to create the model themselves. Many modelling tools have a Accepted: 22 September 2012 very steep learning curve, so the time required to invest in learning a tool to get even a simple result is often prohibitive. In this article, we introduce SketchUp (version 8) as a relatively easy-to-use tool for modelling Citation: St. Clair E, Maloney A, crime scenes in 3D, give an example of how the software can be applied, and provide resources for further Schade A. An Introduction to Building 3D Crime Scene Models information. Using SketchUp. J Assoc Crime Scene Reconstr. 2012:18(4);29-47. Author Contacts: Keywords: Crime scene sketching, 3D visualization, software modelling, crime scene models, SketchUp, [email protected], [email protected], Trimble, crime scene reconstruction, forensic science [email protected] Introduction modelling or computer aided design (CAD) to Computer graphics have been used to enhance produce a meaningful 3D model. As a result, the visualization of shapes and structures across investigators have been limited in terms of a wide variety of disciplines since the 1970s, which scenes they can model in 3D because of when the capability to produce computerized the time-consuming and expensive nature of 3D models was first developed [1]. Shortly after the modelling process. this technological advancement, professionals Fortunately, over the last few years, as in the field of forensics began to utilize investigators have become more comfortable computer modelling techniques to demonstrate interacting with computers and graphics eye-witness accounts and forensic findings software has become easier to use, new during testimony in court [2-4]. However, options have become available to the average until recently, using computer programs to investigator. One tool in particular—SketchUp model in 3D has generally been a complex (version 8)—has really flattened the learning undertaking, usually requiring an expert in curve and made basic 3D modelling available J Assoc Crime Scene Reconstr. 2012:18(4) 29 www.acsr.org to any investigator willing to spend a little time may not have even attended the scene. The learning the software. cost, ease-of-use, and availability of thousands of models in the Warehouse database make Crime Scene Graphics SketchUp a great option for investigators who Crime scene graphics are visual designs need to produce 3D models of crime scenes. intended to illustrate details observed at a physical location. Such graphics communicate Basic SketchUp Concepts spatial relationships to those who did not Before jumping into an example of how to attend the scene and provide an effective way build a 3D model, it is important to understand to document a scene for subsequent analysis some of the basic concepts used in SketchUp. and presentation. They include basic, hand- When SketchUp is started, the user is presented drawn illustrations (commonly called rough with a window allowing the selection of a sketches), intricate, detailed drawings (known drawing template for the project. Templates as final sketches or diagrams), and interactive, do not change the way SketchUp works; they realistic replicas (referred to as 3D models in simply provide a way to set the default scale, this article). style, and color for new projects. Any of these Typical scene sketches and models settings may still be changed after the project present a two-dimensional (2D), top-down is created. SketchUp provides several built-in representation of the scene [5]. While 2D templates for both imperial and metric units, sketches and models are useful for presenting and the user can create and save personalized the spatial information collected at scenes, 3D templates for future use. models can be more effective at communicating When the user creates a new project, they are such information. presented a window displaying three axes, which With SketchUp, the authors propose that represent the x, y, and z axes of the Cartesian investigators who have no professional graphics coordinate system. SketchUp uses three colors training can produce realistic 3D crime scene to represent the different axes: red, green, and models without altering the way they process blue. The blue line represents up and down and the scene and they can even create to-scale 3D the other two make up the ground plane for models if sufficient measurements are available. the model. Each of the axes have a solid line on one side of the origin and a dotted line on the SketchUp’s Background other to help with orientation. These axes act What is SketchUp, and why is it of interest to as guidelines and are used to indicate direction crime scene investigators? SketchUp is a 3D and rotation, to line up objects, and to provide modelling tool originally developed by @Last a visual cue when moving the virtual camera Software in 2000, and acquired by Google in around the scene. 2006 to provide a tool for building 3D models for their Earth and Map projects. In June 2012, The Model and the Camera the rights to SketchUp were purchased by A SketchUp model is simply the virtual 3D Trimble (http://www.trimble.com/). SketchUp world the modeller is creating (the crime scene) is available for both Mac OS X and Windows. which will contain objects such as furniture, Users may download a free version of SketchUp walls, victims, evidence markers, etc. The or purchase the Pro version at http://sketchup. camera moves about this scene, allowing the google.com/download/. user to view objects from any angle. SketchUp While there are many very impressive 3D provides tools to pan, zoom, and move about modelling tools currently on the market, a the scene (these tools are described below). novice modeller with access to the internet SketchUp also provides seven standard views will find the free version of SketchUp easy to that are helpful in positioning the camera at obtain and easy to learn. This means that an specific locations relative to the scene’s axes investigator can learn to create these models and for focusing the camera position on the themselves instead of relying on someone who center of the scene. These views, accessed www.acsr.org 30 J Assoc Crime Scene Reconstr. 2012:18(4) Figure 1 (top left): Top view Figure 2 (top right): Front view Figure 3 (bottom left): Side view Figure 4 (bottom right): Iso view using the Camera->Standard Views menu, are technique that makes your scene appear 3D Top (Figure 1), Front (Figure 2), Back, Left, even though it is seen on a 2D computer screen. Right (Figure 3), Bottom, and Iso (Figure 4). Consider a picture straight down some railroad Another important aspect to viewing the tracks. The tracks appear to meet at a point scene is choosing the camera projection. There in the distance which is called the vanishing are three different camera projections available: point. With a Parallel Projection, however, the Parallel Projection (Figure 5), Perspective apparent depth in the model is removed. This is (Figure 6), and Two-Point Perspective. The especially useful when the modeller would like default camera setting is Perspective, which to produce a traditional, top-down, 2D sketch makes items closer to the viewer appear larger of the scene. Two-Point Perspective uses two than objects further away. This is a visual vanishing points instead of one and is not really Figure 5 (left): Parallel Pro- jection Figure 6 (right): Perspec- tive J Assoc Crime Scene Reconstr. 2012:18(4) 31 www.acsr.org Figure 7 (top left): Shaded with Textures style Figure 8 (top right): Shaded style Figure 9 (bottom left): Monochrome style Figure 10 (bottom right): X- ray style useful for crime scene models, so it will not be Styles discussed here. One of the ways to change the look of the The user may also add custom fixed camera model is to change the style that affects the positions by using the Scene Manager window, edges and surfaces (faces) of the scene. The accessed using the Window>Scenes menu item. options in the View>Face Styles menu allow The plus icon in the upper left corner of the window the user to quickly change the visual style of will create a tab at the top of the viewing window, the model to include textures (Shaded With called “Scene 1.” Clicking on this tab will always Textures, Figure 7) or just show the surfaces return the camera to this saved position. The user as colors (Shaded, Figure 8). Two other very can keep moving the camera to a new position, and useful styles are the Monochrome style (Figure repeating the “add scene” operation until the user 9), which removes colors, and the X-ray style has the desired number of camera positions saved. (Figure 10), which makes the entire model Established scenes may be renamed, rearranged, transparent. The authors have found this a revised, or deleted under the scene manager useful tool when creating visually busy scenes window. Selected scenes may be exported as 2D in that it can simplify the appearance of the images, 3D models, or animated “fly-through” model and make different viewing options videos (see the Advanced Topics section).

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