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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