Label - IFC Mapping Data - Calculation of the Parameter?

[Anonymous]

The pipe has the parameter "Outer Diameter", "Elevation".

As for the "Elevation", this is the center level of the pipe. (Fig. 01)

In the IFC Data Mapping, the "Elevation" could be mapped. (Fig. 02)

In the Label, how to show the bottom level?(Fig. 03) The bottom level is calculated as below

BL = CL - Diameter /2

where BL = Bottom Level
CL = Center Level

[Anonymous]

Fig.02

[Anonymous]

Fig. 03

[Laszlo Nagy]

In the IFC Scheme Settings Dialog it is not possible to define calculated values.
What I would do in such a situation is I would modify the script of the GDL Object: create a new parameter that would story the value I need, calculate it and assign the parameter the calculated value. Then I will be able to use that parameter with the calculated value in IFC Mapping. But for this the GDL Script needs to be modified.