vSite Admin Portal: Custom Coordinate Systems Elevation Settings

When setting up a Custom Coordinate System (CRS) in vSite, two elevation fields must be defined:

  • Local Elevation

  • WGS84 Elevation

These values work together to define the vertical offset between your local CRS and the vertical datum used in your project.

What the Settings Mean

  • Local Elevation
    Represents the reference elevation in your custom coordinate system. Typically, this value comes from your surveyed local dataset.

  • WGS84 Elevation
    Represents the corresponding elevation value in the vertical datum configured for your data source. While this field is labelled “WGS84,” it is not restricted to WGS84 specifically; the actual datum applied is the one set in the data source configuration (e.g., WGS84 ellipsoid, EGM2008, or another supported vertical datum).

How the System Uses These Settings

The two elevation values are compared, and the difference between them is applied as a vertical shift during transformation.

Example:

  1. A data object is collected at 10 m (local height).

  2. Custom CRS settings:

    • Local Elevation = 1 m

    • WGS84 Elevation = 0 m

  3. Data source vertical datum = EGM2008, with geoid undulation of 20 m at this location.

  4. Processing:

    • Apply CRS offset: 10 m – 1 m = 9 m

    • Transform to vertical datum: 9 m in EGM2008 → subtract 20 m undulation = –11 m in WGS84.

Key Points to Remember

  • The difference between Local Elevation and WGS84 Elevation defines the vertical offset.

  • The final elevation is always expressed relative to the vertical datum configured in the data source.

  • If both fields are set to the same value (e.g., 0 and 0), no vertical shift is applied.

  • These settings ensure that custom CRS data aligns correctly with global coordinate systems and vertical datums.

Have Questions? Feel free to Submit A Request to speak with a member of the vGIS Support Team.

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