Forensic Accident Mapping

Cross Examination of Total Station measurements

If it was generated from a proper survey ( forensic mapping ) , which downloaded to a scale diagram, then the following more sophisticated questions should be posed. Here are some of the questions, and of course, the answers that should come back.

1. Question: What type of instrument did you use to measure the scene?
Answer: Nikon, Sokkia, Leica, Topcon along with the model number

2. Question: How do you know the instrument is accurate?
Answer: I test the instrument regularly by using known reference measurements.

3. Question: When was the last time it was calibrated?
Answer: I have the instrument serviced and calibrated yearly

4. Question: Are you trained or certified to operate the instrument?
Answer: Yes, I have taken and successfully completed a forensic mapping course which encompassed the use of the measuring equipment as well as the theory of the technology, and also how to download the measurement data.

5. Question: Can you produce a record of the measurement data that you recorded on this case?
Answer: Yes, I have a complete spreadsheet of all the x,y,z coordinate data which also includes the date and time it was recorded.

6. Question: How can you convince the court that the measurements that you took at this accident scene are precise?
Answer: the instrument is capable of measuring at distances up to 2000 metres to an accuracy of 1 cm, and on this case, I took 2 reference measurements by hand with a tape measure, which I later checked using the downloaded data and found the measurements were precisely the same.

7. Question: How do we know the diagram that you have generated is to scale?
Answer: If you look at the scale bar you will see that it represents what 100 feet covers in the real world. If you then use that scale bar to measure any distance you will see that the scale bar is precisely representing that distance.

8. Question: What is the scale of the diagram?
Answer: The scale is 1: 200 ( or any other number ).

9. Question: When you downloaded the measurements to the diagram that you created, how do you know the software represents the scene accurately?
Answer: I used the software to measure between the known reference points and found the distances to be precisely the same.

Cross Examination of hand measurements

If the measurements were generated from hand measuring, which resulted in a diagram then the following series of questions may be included in the cross examination.

1. Question: Please explain your measuring procedure.
Answer: I established a straight baseline or reference line at the scene, and then measured along the line and at 90 degrees to the line to the measurement points to establish precise x,y positions of all points.

2. Question: Did you measure the vertical position of each point?
Answer: No, this procedure only measures 2 dimensionally.

3. Question: So, your procedure assumes the scene is a flat plane?
Answer: yes, there is no way to measure vertical positions or angles by hand.

4. Question: How accurate is this procedure:
Answer: it is accurate within about 1 foot on most measurements.

5. Question: When you measure to the evidence or other points at an angle of 90 degrees from the baseline, how do you know you are really at 90 degrees?
Answer: It is estimated.

6. Question: if your measurements from the baseline are taken at an angle different than 90 degrees what is the effect in terms of accuracy?
Answer: the measurements are not accurate if that is the case.

7. Question: If your measurements are accurate only within a tolerance of 1 foot, what would be the error factor on the calculations regarding speed etc?
Answer: the range of accuracy would reflect the scene measurement accuracy.

Measurement Logs

Here is an example of a measurement log, which details each measurement point in terms of its x,y,z position as well as it’s description.

See a Sample Measurement Log

Also see how the diagram should appear which shows the measurement points, which correspond to the log.
Finally, click here to see what a proper 3D model of an accident should look like after being processed by a professional re-constructionist using state of the art measuring equipment and software.