Understanding Trilateration

This is a basic concept you must understand before installing the GrowSpace UWB-based RTLS system.

What is Trilateration?

Trilateration is a method of calculating the position of a tag by using the distance between the tag and three or more anchors. This is the most common and accurate method used in UWB indoor positioning systems.

How It Works

1. Tag → Anchor: Signal Transmission

• The tag sends a UWB signal.

• Surrounding anchors receive this signal.

2. Anchor → Tag: Distance Measurement

• Each anchor measures the distance to the tag.

• The distance is calculated based on the Time of Flight (TOF), which is the time it takes for the signal to travel.

3. Position Calculation

• The distances from three or more anchors are used to calculate the tag position.

• The calculation uses the concept of circle intersections.

Example:

• If anchors A, B, and C are 3m, 4m, and 5m away from the tag:

  • Draw three circles centered on A, B, and C.

  • The point where the three circles intersect is the tag location.

Important Installation Notes

• Use at least three anchors

  • Trilateration does not work with fewer than three anchors.

• Enter accurate anchor coordinates (X, Y, Z)

  • Incorrect coordinates will cause inaccurate RTLS results.

• Do not omit the Z coordinate

  • Position is calculated in 3D space.

  • Missing the Z (height) value will distort distance measurements.

• Minimum distance between anchors: 2 meters

  • If anchors are too close, calculation accuracy decreases.

• Keep tags inside the anchor coverage area

  • Position accuracy drops near the edges of the installed area.

Practical Example

Anchor Coordinates:

• A: (0, 0, 2)

• B: (6, 0, 2)

• C: (3, 5, 2)

Tag Position:

• (3, 2, 1.5) → Calculated using trilateration.

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Common Issues and Causes

RTLS position jumps	Too few anchors, wrong coordinates, or obstacles
Distance measured but no position	Less than 3 anchors or missing coordinates
Tag shown outside walls	Asymmetrical anchor placement or tag near edge area