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IfcProjectedCRS - EPSG code not known

ifc4
#1

I’m having difficulties implementing IfcProjectedCRS and would like to hear your thoughts on it.

First, find the entity here: IFC4_add2_TC1 - IfcProjectedCRS
or here, as a part of RV1.2: IFC4_add2_TC1 - RV1.2 - IfcProjectedCRS

What I am having difficulties with, is an instantiation of the entity if the EPSG code of the underlying coordinate reference system is not known. For example, a user has data in WGS84 projected by UTM 32N (EPSG:32632) and EVRF2007 (EPSG:5621). I can fill up all the parameters of IfcProjectedCRS, except for the MANDATORY Name attribute, since currently there is no such combination as an entry in EPSG database. I also cannot put in any of the codes provided above, since this is only partial information. The reading application will most probably merely look at the Name attribute, since all the rest is nice to have.

What is the correct way of doing this? Must I write an email to EPSG database in order to get this combinatoin added? Should we change the Name attribute to OPTIONAL and include a WHERE rule that Name or GeodeticDatum+VerticalDatum+MapProjection+MapZone need to be filled with data? Or something of sort? I would be happy to hear your thoughts on this.

#2

Hello Stefan,

for the usage of CRS systems in IFC the definition is based on the GML standard.
Here a simple example from a CityGML file:
srsName=“urn:ogc:def:crs,crs:EPSG:6.12:25832,crs:EPSG:6.12:5783” srsDimension=“3”
Transferred to ifc the Name should look like:
IFCPROJECTEDCRS(‘EPSG:25832,EPSG:5783’,‘Some description’,?,?,?,?,?)