Setting Up in the Real World – GeoReferencing by Footprint

Series Index - Setting Up in the Real World

Following the techniques used in Setting Up in the Real World – GeoReferencing Update, a similar approach uses individual facility/building footprints as the guiding geometry.

This allows the individual facilities to be moved around independently by updating their geographic transform or if plan position is fixed allows the z height to be adjusted using the reference Z offset value

Having created the site plan, GR1-BSUK-00-ZZ-M3-C-0001.dgn, and attached the appropriate geographic coordinate system; instead of drawing arbitrary site alignment geometry, draw the facility/building footprints. In this example there are three footprints colour coded for identification:

Then create a setting out plan for each of the facilities showing the facility footprint at exactly the same size but placed unrotated, at or near the Design File Centre;

  • GR1-BSUK-F1-ZZ-M3-C-0001.dgn
  • GR1-BSUK-F2-ZZ-M3-C-0001.dgn
  • GR1-BSUK-F3-ZZ-M3-C-0001.dgn

Here is Facility 1:

Attach the site plan  GR1-BSUK-00-ZZ-M3-C-0001.dgn to each of the facility plans. Move and rotate the site plan so the appropriate site footprint is coincident with the facility plan footprint:

Use 'Geographic Coordinate System > From Reference' to create the Local Transform for Facility 1.

Repeat for Facilities 2 and 3.

Carry out detailed building modelling operations for each of the facilities.

To see all three facilities in their site context reference them into site plan, GR1-BSUK-00-ZZ-M3-C-0001.dgn, and attach using the 'Geographic - AEC Transform' method (this can be done in one step in the Reference dialog by selecting all three facility models, picking the 'Geographic - AEC Transform' method then clicking OK):

Note that Facility 3 (in orange) has additional building related to the main structure. The footprint is used for alignment, it does not clip the model so the chosen footprint does not restrict the model.

Then say a major repositioning of facility 3 was required, simply repeating the alignment process to update the transform to the new location places the referenced Facility 3 in its new position:

Back in the individual facility models, they can all be referenced to each other using the same 'Geographic - AEC Transform' method so the relationships between them are available when working at the detailed model scale:

The site information can also be referenced into the detailed models using the same 'Geographic - AEC Transform' method:


Once a transform has been created for a project, first of all ensure that it is documented so that the originating design team have a clear record of what was done. This will reduce the risk of error later in the life of the project. Create a document suitable for sharing with other project participants that clearly communicates how the GCS was established.

There is no need to attach the project GCS to all project files, only to those container or model files that actually need to be related to the site plan.