Vertical Offset


Data source: EPSG

Information source: EPSG guidance note #7-2, http://www.epsg.org

Revision date: 2017-10-16

Remarks: This transformation allows calculation of height (or depth) in the target system by adding the parameter value to the height (or depth)-value of the point in the source system.


Note: These formulas have been transcribed from EPSG Guidance Note #7-2. Users are encouraged to use that document rather than the text which follows as reference because limitations in the transcription will be avoided.

A vertical offset allows calculation of coordinates in the target vertical coordinate reference system by adding a correction parameter A to the coordinate values of the point in the source system:
X2 = X1 + A1>2
X2 = value in the forward target vertical coordinate reference system.
X1 = value in the forward source vertical coordinate reference system.
A1>2 is the offset to be applied for the transformation from CRS 1 to CRS 2. Its value for the forward calculation is the value of the origin of the source CRS 1 in the target CRS 2.

For the reverse transformation from CRS 2 to CRS 1 the same formula is used but with the sign of the offset A1>2 reversed:
	X1 = X2 + (–A1>2)

The above formulas apply only when the positive direction of the axis of the source and target CRS is the same and where the two vertical CRSs share the same unit of measure. If either of these are to be changed then a concatenated operation including one or more conversions through intermediate vertical CRSs is required. See Height-depth reversal (code 1068) and Change of vertical axis unit (code 1069) for the required conversion methods.


For coordinate transformation: Baltic height to Black Sea height (1), code 5447:

Transformation Parameter:	Vertical Offset      A1>2 	=	0.4m

Consider a point having a gravity-related height in the Baltic height system of 2.55m. Its value in the Black Sea height system is
2.55m  + 0.4m = 2.95m.

For the reverse calculation to transform the Black Sea height of 2.95m to Baltic height:
H(Baltic) =  2.95m + (–(0.4m)) =  2.55m.
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