GPS/GNSS Geometry – Satellite distribution for accurate 3D fix For a precise position fix using three satellites (for example, in trilateration with aiding), what geometric arrangement yields the best accuracy and lowest dilution of precision (DOP)?

Introduction / Context:
Global Navigation Satellite System (GNSS) accuracy depends not only on measurement precision but also on satellite geometry. Poor geometry amplifies range errors into large position errors, quantified by dilution of precision (DOP) metrics such as GDOP, PDOP, HDOP, and VDOP.

Given Data / Assumptions:

• At least three satellites contribute ranging signals (with clock or altitude constraints).
• Receiver has clear sky view with minimal multipath.
• Equal range error variance for simplicity.

Concept / Approach:

Wide angular separation among satellites enlarges the intersection angles of range spheres, making the solution less sensitive to individual range errors. This reduces DOP. Clustered or nearly collinear satellites produce ill-conditioned geometry and higher DOP values, degrading the fix.

Step-by-Step Solution:

Verification / Alternative check:

GNSS planning tools show PDOP minima when satellites are widely separated; PDOP spikes when satellites cluster.

Why Other Options Are Wrong:

Common arc/vertical stacking/collinearity yield high DOP; “one overhead plus two close” is still weak distribution.

Common Pitfalls:

Ignoring geometry while focusing only on signal strength; not accounting for elevation masks and obstructions.

Final Answer:

Satellites widely separated and well distributed around the sky