Overview

The BLEND parameter group (specifically GPS_BLEND_MASK) configures the Dual GPS Blending logic.

When two GPS units are installed, ArduPilot can "blend" their outputs to create a single, smoother, and more robust position solution for the EKF. This is distinct from "GPS Switching" (Best Available).

Key Concepts

1. Weighting Logic

The blended solution is a weighted average of the two sensors. The weights are calculated based on the reported accuracy (uncertainty) of each receiver.
$$ P\_{\text{blend}} = \frac{P\_1 \cdot W\_1 + P\_2 \cdot W\_2}{W\_1 + W\_2} $$
where $W = 1 / \text{Accuracy}^2$.

2. Blending Mask (GPS_BLEND_MASK)

This bitmask determines which accuracy metrics are used to calculate the weights.

• Bit 0: Horizontal Position Accuracy.
• Bit 1: Vertical Position Accuracy.
• Bit 2: Speed Accuracy.

Parameter Breakdown

• GPS_BLEND_MASK: Controls weight calculation.
  • 5 (Default): Use Horizontal Pos + Speed accuracy. Vertical accuracy is often ignored because GPS altitude is notoriously noisy.

Integration Guide

• Requirement: Two GPS units (GPS_TYPE and GPS_TYPE2 set).
• Activation: Set GPS_AUTO_SWITCH = 2 (Blend).
• Verification: Check GPS2 status in GCS. The "Blended" solution is what the EKF consumes.

Developer Notes

• Library: libraries/AP_GPS/AP_GPS_Blended.cpp
• Prefix: GPS_BLEND_ (often aliased or grouped here).