# Demo — Geolocation Explorer
One bearing is a line; cross two and you have a fix. But the *quality* of that fix is set almost entirely by geometry — the angle at which the bearings cross — not by how good the receivers are. This demo lets you drag the receivers and the emitter and watch the error ellipse breathe.
## The idea
Each receiver gives a line of position with an angular uncertainty band. The fix lives where the bands overlap, and the shape of that overlap is governed by the **cut angle**: near $90^\circ$ gives a tight, near-circular error; a shallow cut smears it along range.
## Interactive demo
Open in full screen
## Walkthrough
1. **Start with a good cut.** With the emitter abeam the receiver pair, the two bearings cross near $90^\circ$ and the error ellipse is small and round. Note the CEP readout.
2. **Push the emitter downrange.** As it moves far from the baseline, the cut angle shrinks, the ellipse stretches along the line of sight, and CEP grows — the *same* receivers now do far worse.
3. **Drag onto the seam.** Move the emitter onto the receivers' baseline. The cut collapses, range becomes unobservable, and the fix runs away — the geometry has failed, not the hardware.
4. **Widen the baseline.** Drag one receiver out perpendicular to the line of sight to reopen the cut toward $90^\circ$ and watch the ellipse tighten again.
## Key observations
- **Geometry sets the error, not receiver quality.** This is the whole lesson — the receivers never change in the type-along; only the geometry does.
- **A shallow cut smears error along range.** Cross-range stays decent; downrange blows up.
- **Wide baselines hold a strong cut at long range** — exactly the standoff geometry Project 2 exploits to geolocate from outside the threat rings.
## Source
MATLAB · code/L14_TwoReceiverCrossFix.m↓
The in-class script crosses two noisy bearings into a fix, repeats it thousands of times to map the error cloud, then moves the emitter downrange to show the same receivers degrade as the cut angle shrinks.