Chapter 16 | Importing Total Station Measurements
Introduction
In Virtual CRASH 3 the user can import .dxf files into the simulation environments. These .dxf files can contain measurements captured during laser surveys of accident scenes. In this write-up we demonstrate how one can easily import total station measurements to help build your simulation scene.
The final animation of this crash can be found online:
First, we obtained an aerial photograph of our accident scene using Google Earth [1]. This was imported into Microsoft Paint by performing a simple screen capture [2]. Background vehicles were removed, and the image was cropped to focus on the road itself (see next two figures below).
Import Measurements into Spreadsheet Utility
Virtual CRASH 3 can import your total station measurements directly. Virtual CRASH 3 assumes your file is in ASCII format with a “.pts” extension and has one of four formats such as the one shown in (see below). Virtual CRASH 3 can support (No., x,y,z, text), (x,y,z), (No., x,y,z,), or (x,y,z,text).
Import Total Station points to spreadsheet and format
For this reconstruction, a Northwest Instrument, Inc. [3] total station was used to conduct a scene survey. The data points were easily imported into spreadsheet format using Google Sheets to remove extraneous data columns (small sample of points shown in figure above) [4]. In this case, the total station exports the measurements in meters. To import your .pts file, go to the “Import” command under “Project.”
Ensure the file type is set to “.pts” in the lower right corner.
You will then see an import dialog box appear.
Here you can set the units that your measurements were taken in. You can also specify the file format, text and point sizes, and flip the horizontal or vertical axis of your data if necessary. In this case, we will need to flip the horizontal axis of the data.
Once the file has been imported, you will see separate text, numbers, and points objects defined in the objects list in the left side control panel.
In your environment, you will see the points, numbers, and point labels all drawn together.
These will all be selected after the points are imported, so you can move all three elements around the scene to position and orient as needed. You can also hide the text, numbers, or points themselves, as well as change the color of your points. In the figure below, both the descriptive text and point numbers have been hidden.
By selecting the points object, you can change the color property in the left-side control panel.
Orient Your Points
Next, using the top down orthographic view, rotate and translate your points until you’ve aligned them with various key features within your scene. In this example, measurements were taken of the lane lines as well as utility and traffic signal poles. Using the utility and traffic signal poles as fixed references, it is easy to ensure proper alignment of our points with respect to the aerial photo. Once you are satisfied with the alignment of your measurements with your aerial photo, freeze the Total Station measurement points.
Add Asphalt, Striping, and Other Elements
Now that you’ve aligned your points with fixed references within the aerial photo, you can overlay an asphalt textured polygon shape, drawing striping patterns, and place other graphical elements within your scene [5].
In our subject accident, a distracted driver of a passenger car rear-ended a tractor-trailer that was at rest for the traffic signal ahead. The undercarriage of the car left gouges in the asphalt characteristic of hard metal components being forced downward against the asphalt during the collision. The two vehicles were then mechanically locked together. The tractor-trailer moved upon a green signal, dragging the car behind as the two remained locked together, creating a long groove in the asphalt (see next four figures below).
Advanced Simulation Techniques
Add New Simulation Point
We want to simulate and animate the subject accident, but there is no mechanism to cause the vehicles to lock together after the initial impact. One approach is to split up the simulation into two separate events: the first event ends after the passenger car comes to rest at the rear of the trailer, which begins your second event. First save your current file. Then save the file again to a new file name. In this new file, starting at the final moment in the simulation, set up a new “Simulation Point” by left-clicking Create > Physics > New Simulation Point.
Your new simulation file will now have its starting point corresponding to the end state of the previous file. Re-save this new file.
Lock Vehicles Together with Spherical Joints
Next, we need to lock the two vehicles together such that when the tractor accelerates forward, the passenger car moves forward attached to the trailer. Arrange your camera so that you can see both the front of the passenger vehicle and the rear of the trailer simultaneously. Left-click on Create > Physics > Spherical Joint [6]. On the passenger side of the trailer, hover your mouse over the trailer so that it turns blue in color. Left-click and hold on the corner of the trailer, drag your mouse to the front-end of the passenger vehicle such that the passenger vehicle turns blue.
Release the left-mouse button and this will create a spherical joint connecting the two. Create a second spherical joint to connect the driver sides. This should be sufficient to force to two vehicles to move together.
Insert Tractor Acceleration in Sequences Menu
Now left-click on the tractor, and under the sequences menu, insert an acceleration value so that the tractor-trailer-vehicle system moves forward [7].
Select the Path for the Tractor
Using a clone of the groove line shape, extend the clone out into the intersection to make a path for the tractor to follow. Left-click on the tractor, and under the sequences menu, left-click on “pick path” then left-click on the path. This will cause the auto-driver system in Virtual CRASH to follow the path indicated by the groove [8]. Your tractor-trailer-vehicle system should now follow the path indicated by the evidence left in the asphalt.
Insert a deceleration event in the tractor’s sequences menu to bring the system to rest such that the passenger vehicle’s engine compartment is over the engine fluid stain observed at the area of rest.
Notes:
[1] The process of importing Google Earth (or scale diagrams) is described in Chapter 9 | Scaling Images and can also be seen at: https://youtu.be/z5utwWWcMCE
[2] You can obtain a copy of this background at: http://www.vcrashusa.com/s/GoogleEarth_ImportingMeasurements.png
[4] You can obtain a copy of the points in ASCII format at: http://www.vcrashusa.com/s/TOTAL_STATION_POINTS_ImportingMeasurements.pts
[5] Drawing techniques within Virtual CRASH 3 are demonstrated online at: https://youtu.be/cpan8p7mVNA
[6] You can find an example of connecting objects by joints online at: https://youtu.be/-OLhVek-W0Y?t=542
[7] You can find more information on using vehicle controls see Chapter 8 | Vehicle Controls.
[8] You can find a videos demonstrating the auto-driver system online at: https://youtu.be/Z0EtlHQIAs0, https://youtu.be/1xsFI3OpG7c, and https://youtu.be/p7fbDJVTSf4.
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