City2BIM Georeferencing

With the help of the georeferencing functions, a superordinate (or local) referencing is transferred to the Revit project. The values to be set individually have an influence on various Revit parameters, which are explained in more detail below.

Further information on georeferencing in BIM and in particular in IFC (Level of Georeferencing) can be found here (link to GitHub repository). A tool for checking or changing the georeferencing in IFC files is also available there.

Revit - Tool Overview

In Revit via the following ICON you can access our georeferencing tool.

The actual tool looks like this:

We support the following use cases:

• Postal Address input (work in progess)
• Geographic site coordinates
• Projected coordinates
• Elevation
• Transformation WGS84 <--> UTM

---

Postal Adress input

Currently, Revit internal storage is unfortunately not implemented yet, as Autodesk considers addresses differently between the versions of the last years. It is planned to enable saving of data internally in Revit in equivalent parameters in following versions.

---

Geographic site coordinates (Latitude & Longitude)

Simple transfer of a point reference in WGS84 in latitude/longitude format for rough georeferencing. Entering the values changes the revit-internal location of the project, which can also be retrieved as follows:

• Manage -> Project Location -> Location

The entered values are taken over there, see picture:

In addition, the rotation ("Angle to True North") in the project base point is adapted for the Revit XY coordinate system.

If the project is to be exported to IFC, this coordinate is written to the "IfcSite" entity in the "RefLatitude" and "RefLongitude" attributes.

The coordinate is the equivalent of the Revit project base point in WGS84. It also serves as a reference during the server-based import of city model data, from which area city model data is to be retrieved.

---

Projected coordinates

Possibility to transfer geodetic (or also local) coordinates for the import of geodata. Also the storage of a georeferencing in a geodetic coordinate reference system.

The input/calculation of the values has the following influence within the Revit project:

• Setting the project base point (Eastings, Northings)
• Storage of the coordinates as well as the data on rotation, scale and EPSG code as project parameters
• Consideration of the scale when importing geodata via the plugin (the scale is "calculated out", in Revit the scale is internally always equal to 1.000000)

Project base point coordinates, take over from:

• Eastings
• Northings
• Orthometric Height
• True North (adapted to Revit-XY)

---

Elevation

Possibility to enter a project height as well as a height reference system. The input/calculation of the values has the following influence within the Revit project:

• Setting the project height in the project base point
• Storage of the project height, the reference system as project parameters

Save as project parameter, Manage --> Settings --> Project Information:

The parameters are created by the plugin and are based on how a georeferencing is to be transferred to IFC. If the currently implemented IFC export option is used later, the georeferencing can be transferred in a standard-compliant manner as an IFC property set with revit's own IFC exporter.

The data should not be changed manually at this point. The stored values for the rotation in XAxisAbscissa and XAxisOrdinate refer to angles from grid north converted to vector notation. (Note the difference between True North and Grid North e.g. for sun position analyses).

---

Transformation between: WGS84 <---> UTM

In addition to the input options, the plugin offers the possibility to calculate country coordinates from WGS84. This is helpful, for example, if no coordinates are (yet) known in the current system. The calculation is also possible in reverse order (see picture above).

The following parameters are calculated:

• eastings, northings from latitude, longitude or reverse
• Grid North from True North (also lLongitude*) or reverse (Considering the meridian convergence)
• Scale, scale calculation, depending on meridian (longitude or eastings) and project height (orthometric height)

Requirement:

• Selection of a predefined EPSG code (corresponding to the ETRS89_UTM national systems in zone 32 or 33 in Germany) Outlook: automated calculation via further EPSG code (work in progress)

---