Skip to content
Bedrock

Spatial reference systems

Geospatial data achieves its spatial awareness through Spatial Reference Systems (SRS), standardized definitions that link coordinates to real locations on Earth.

Geographic SRS
Coordinates in degrees (Longitude, Latitude, Height)
  • Example: WGS84 (used by GPS)
  • Global coverage but distance measurements are complex
Projected SRS
Coordinates in meters (Easting, Northing, Height)
  • Example: UTM Zone 31N, British National Grid
  • Regional coverage but distance measurements are straightforward

Geotechnical projects typically use projected coordinate systems that match local survey practices, making integration with engineering workflows seamless.

Vertical Datums

Section titled “Vertical Datums”

While horizontal coordinates (easting and northing) reference locations on Earth’s surface, elevation values (Z) rely on a vertical datum—a defined reference surface for measuring height. Choosing the correct vertical datum ensures that depths, ground levels, and cross-section alignments are consistent across datasets and disciplines.

There are two main types:

Ellipsoidal height
Measured from a mathematical model of the Earth's shape (e.g., WGS84 ellipsoid). Common in GPS systems but not suitable for engineering unless converted.
Orthometric height
Measured from a defined sea level (e.g., NAVD88 in the US, NAP in the Netherlands). This is the standard for most geotechnical and civil engineering work.
For example:

GPS-derived elevations often reference the WGS84 ellipsoid and must be converted to orthometric heights using a geoid model.

In the Netherlands, elevation is typically referenced to NAP (Normaal Amsterdams Peil), the national height datum.

Why it matters

Section titled “Why it matters”

Misalignment between vertical datums can introduce errors of tens of meters, especially in flood-prone or coastal regions.

Accurate borehole logs, cross sections, and groundwater level interpretations depend on consistent vertical referencing.

Integrating data from multiple sources (surveying, LiDAR, CPT logs, BIM models) requires awareness of both horizontal and vertical CRS.