Vertical Datum Setup
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Vertical Datum Setup
This dialog is used to set up a vertical coordinate system which can contain any combination of an absolute height model, a relative height model and a manual/fixed offset.
This will result in a compound coordinate system which contains either a projected or geographic horizontal coordinate system and the configured vertical coordinate system.
Geoid Height Model
Use the drop down menu to select a Geoid Height Model.
If you have not set the Vertical Coordinate System, it will automatically be set based on the vertical coordinate system of the model.
Height Correction Model
Use the drop down menu to select a Height Correction Model.
Selecting a relative height model will override the Vertical Coordinate System according to the vertical coordinate system of the Height Correction Model.
Fixed Height Offset
Tick the checkbox to enable entry of a Fixed Height Offset. Enter a number directly or use the spin box to change the value.
Vertical Datum
You can set the Vertical Datum using the Search button 
Note that this is typically set via your choice of the Geoid Height Model and/or Height Correction Model.
Datum
The Datum is for information purposes only and is the datum associated with the Vertical Coordinate System.