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.