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Area-of-Origin Stringing

Run the Area-of-Origin Stringing MicroSim Fullscreen

About This MicroSim

Once an analyst knows the direction and angle of impact of several bloodstains, those stains can be traced backward through space to locate where the blood came from. Classically this was done with physical strings pinned to each stain and run back at the measured angle; the place where the strings cross is the area of origin of the source.

This MicroSim shows a pseudo-3D room with five floor stains. Add a string to each stain, then find the point in the air where they converge — and read its x, y, z position in metres.

How to Use It

  1. Click a stain on the floor to read its width, length, and calculated angle of impact.
  2. Press Add String to project a string back from each stain (in order) at its angle.
  3. With at least two strings up, press Find Intersection to highlight the green convergence zone and read its (x, y, z) coordinates.
  4. Drag the Source height slider and watch the strings re-slope and the convergence zone rise or fall. Press Reset to start over.

What You Can Learn

  • Apply stain direction and angle-of-impact data to locate a source in 3D.
  • Explain why multiple stains are needed — a single string only gives a line, not a point.
  • Interpret the convergence height (about 1.2 m here) as evidence about the source's position, such as a standing or seated person.

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

<iframe src="https://dmccreary.github.io/forensic-science/sims/area-of-origin-stringing/main.html"
        width="100%" height="502" scrolling="no"></iframe>

Lesson Plan

Audience: High-school forensic science (grades 9–12) Time: 15–20 minutes Bloom level: Apply (L3) — determine the area of origin.

Walk-through. Add strings one at a time and ask the class to predict where they will cross before pressing Find Intersection. Then move the height slider and discuss how the convergence point tracks the true source.

Guided questions:

  • Why does one string alone fail to pin down the source?
  • The convergence sits about 1.2 m above the floor. What does that suggest about the source's height?
  • If a stain's angle were measured incorrectly, what would happen to the convergence zone?

Extension. Connect this to the Angle-of-Impact Calculator: the angle each string uses comes directly from a stain's width-to-length ratio.

References

Specification

This MicroSim was generated from a specification in Chapter 7: Bloodstain Pattern Analysis.

Design note: the room uses a 2D axonometric projection rather than true 3D. The five strings are constructed to pass through one source point so the convergence is clean for teaching; instead of per-stain angle sliders (which would prevent convergence), a single Source height control moves the true origin so students can watch the strings and convergence zone respond.