Measurement:Elevation

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Node Elevation Measurement

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1. Context

In field deployments, it may appear convenient to use smartphone GPS readings to determine the elevation of pipe network nodes.

However, GPS-based altitude measurements are often insufficient for infrastructure-grade water systems due to:

• low vertical accuracy in consumer devices
• atmospheric variation
• inconsistent reference datums
• drift over time

As a result, relying solely on GPS elevation can lead to incorrect hydraulic modeling and unsafe system behavior.

2. Normative Requirement

All AOWIS-compliant systems:

• MUST NOT use uncalibrated consumer GPS altitude as the sole source of node elevation data for hydraulic or control decisions
• SHOULD use surveyed or externally validated elevation references where available
• MAY use GPS-derived elevation only as a temporary or fallback estimate, clearly marked as low-confidence

3. Measurement Model

Node elevation values MUST be represented as:

• a numeric value relative to a defined vertical datum
• associated metadata indicating source type
• optional uncertainty or confidence indicator

4. Reference Hierarchy

Preferred sources for node elevation:

1. Geodetic survey measurements 2. Local infrastructure engineering records 3. Differential GPS or RTK systems 4. Consumer GPS (fallback only)

5. Traceability

The restriction on GPS-only elevation sources exists to prevent:

• hydraulic miscalculations
• incorrect pressure modeling
• unsafe valve/pump control decisions