When establishing the most accurate control point would you want to use the EL or ORTHO height provided by OPUS?
Both heights serve different purposes and are used in different contexts.
Ellipsoidal (EL) Height:
Refers to the height above or below the reference ellipsoid, which is a mathematical representation of the Earth’s shape.
Derived directly from GNSS (Global Navigation Satellite System) observations without requiring any additional geoid model.
Orthometric (ORTHO) Height:
Represents the height above mean sea level (MSL).
Requires the use of a geoid model to relate the ellipsoidal height (from GNSS observations) to the orthometric height.
The geoid represents an equipotential surface of the Earth’s gravity field, which closely matches mean sea level.
So, which one to use for the most accurate control point?
If you’re working on projects that require elevations relative to mean sea level (such as floodplain mapping, engineering projects, construction, etc.), then you would want to use the Orthometric height. This is the more commonly used height for many practical applications because it relates directly to gravitational equipotential surfaces, which influence water flow, and it’s more intuitive for most users.
If you’re conducting geodetic or GNSS-related studies, where relative positions between points are more important than their absolute elevations, or where you’re integrating with other GNSS datasets, then you might use the Ellipsoidal height.
When establishing control points for accuracy, especially when using tools like OPUS, the typical practice in many surveying applications is to use Orthometric heights. This is because they relate directly to physical topography and are consistent with traditional notions of elevation above sea level.
Thank you for the detailed explanation!