Skip to content

Triangulation Measurement Technique

Run the Triangulation Measurement MicroSim Fullscreen

About This MicroSim

When investigators document a crime scene, they have to record exactly where each piece of evidence was found — accurately enough that the scene could be reconstructed later in court. One standard method is triangulation: measure the straight-line distance from the item to two fixed reference points (often two corners of the room). Those two distances pin the item to a single spot.

This MicroSim is an overhead floor plan with two reference corners, A and B. Drag the orange evidence item anywhere in the room and watch the two distances update in real time — calculated with the Pythagorean theorem — then record each item to a measurement log, just like filling in a sketch sheet.

How to Use It

  1. The room is shown from above with a 1-meter grid. Corner A (green, upper left) and corner B (green, upper right) are the fixed reference points.
  2. Drag the orange evidence dot (E) anywhere inside the room. The two blue dashed lines show its distance to A and to B in centimeters, and the dot shows its (x, y) coordinates measured from corner A.
  3. Use the Width and Length sliders to resize the room (3 m to 10 m). The distances and coordinates recompute for the new layout.
  4. Press Record Measurement to add the current item to the measurement log with its number and its distances to A and B.
  5. Press Clear Log to start a fresh sketch sheet.

What You Can Learn

  • Apply the triangulation method: two distances from two fixed points locate an object.
  • See the Pythagorean theorem in action — distance = √(x² + y²) from a corner.
  • Read measurements off a scaled plan in real units (centimeters).
  • Understand how investigators document several evidence items on one sketch.

You can embed this MicroSim on your own web page with this iframe:

<iframe src="https://dmccreary.github.io/forensic-science/sims/triangulation-measurement/main.html"
        width="100%" height="602" scrolling="no"></iframe>

Lesson Plan

Audience: High-school forensic science (grades 9–12) Time: 8–12 minutes Bloom level: Apply (L3) — calculate.

Worked example. Leave the room at 6.0 m × 5.0 m and drag the item to the exact center. Both distances read 391 cm. Check it by hand: the item is 3.0 m across and 2.5 m down from corner A, so the distance is √(3.0² + 2.5²) = √15.25 ≈ 3.91 m = 391 cm. Because the item is centered left-to-right, the distance to B is the same.

Guided questions:

  • Drag the item into the corner at A. What is the distance to A? Why?
  • Move the item straight down the left wall. Which distance changes faster, the one to A or the one to B? Why?
  • Place the item 200 cm right of A and 150 cm down. Predict the distance to A before reading it, using the Pythagorean theorem, then check.
  • Why do investigators measure to two reference points instead of just one?

Extension. Record three evidence items at different spots, then widen the room with the slider. Explain why the recorded distances would change if you re-measured — and why a sketch must always note the reference points and the room dimensions, not just the distances.

References

Specification

This MicroSim was generated from a specification in Chapter 2: Crime Scene Investigation and Evidence Collection.

Design note: the room is a simplified rectangular plan and distances are straight-line ("as the tape measures") values. Real triangulation uses permanent, clearly described reference points and at least two measurements per item, and the sketch is later drawn to scale with all dimensions recorded.