How to export your IFC project with correct georeferencing information in Revit

Masterplan Jan 18, 2021

Georeferencing in Revit

There are two different options for giving spatial information to a Revit Model. One is by linking a georeferenced DWG file (CAD, CIVIL 3D) or by using the survey point and project base point feature present in Revit. The survey coordinate system provides a real-world context for the building model. It is intended to describe locations on the surface of the earth. The project coordinate system describes locations relative to the building model. It uses a selected point within the property boundary or within the extents of the project as a reference for measuring distances and positioning objects in relation to the model.The origin of the internal coordinate system provides the basis for the survey and project coordinate systems. You can also use a shared coordinate system to position imported or linked models in relation to a host Revit model.

Survey coordinate system

You can use the survey coordinate system to identify the specific location on the earth's surface where your Revit model resides. This coordinate system is defined outside the context of a project. Many survey coordinate systems are standardized. Some systems use latitude and longitude; others use XYZ coordinates. Survey coordinate systems handle significantly larger scales than project coordinate systems and deal with issues such as the curvature of the earth and terrain, which are insignificant to project coordinate systems. In Revit, the survey point  identifies a real-world location near the model. For example, you can place the survey point at a corner of the project site or at the intersection of 2 property lines, and specify its real-world coordinates.The survey coordinate system is synonymous with the following terms used by other software applications or in other contexts:

  1. Global coordinates
  2. GIS coordinates
  3. Grid coordinates
  4. Surveyor coordinates
  5. Projection coordinates
  6. State plane
  7. Shared coordinates
  8. Project coordinate system

Project coordinate system

You can use the project coordinate system to determine the position of objects relative to a specified point near the model. This coordinate system is specific to the current project. In Revit, the origin of the project coordinate system is the project base point . Many teams use the project base point as a reference point for measurements across the site. Place it at the corner of a building or another convenient location in the model to simplify on-site measurements. Revit's project coordinate system is synonymous with the following terms used by other software applications or in other contexts:

  1. Local coordinates
  2. World Coordinate System (WCS)
  3. World coordinates (in a DWG context)
  4. User Coordinate System (UCS)
  5. User coordinates
  6. Design coordinates
  7. Model coordinates
  8. Engineering coordinates
  9. Internal coordinates
  10. CAD coordinates

To take advantage of weather station data, accurate sun and shadows, and site referencing in Revit, you have to manually go to the location settings and specify the Site. You can do this by:

Specifying the geographic location

Without linking DWG file

  1. Click Manage tab/ Project Location panel/ (Location).
  2. On the Location tab, for Define Location by, select one of the following:
  3. Default City List: Allows you to select a major city from a list, or enter a longitude and latitude.
  4. Internet Mapping Service: Allows you to select a location using an interactive map, or enter an address. (Requires an Internet connection.)

Note: If this option is set to Get Location From Survey Point, coordinates from a linked DWG file define the survey point and the geographic location for the model. The GIS Coordinate System, Latitude, and Longitude fields display location information acquired from the DWG file.

3. Enter or select the desired location.

4.Optional: For energy analysis, select a nearby weather station from the list.

Note: To see weather stations in the map and in the list, you must be signed into your subscription-enabled Autodesk account.

5.If the model is located in an area that observes daylight saving time and you want shadows to be adjusted accordingly, select Use Daylight Saving time.

6. Click OK.

Revit 2018 has the ability to use Georeferenced survey data from a linked DWG file.

Requirements: A georeferenced CAD file from Autocad or Civil 3D.

Steps (Revit 2017):

  1. Open Revit 2017
  2. Go to Insert option
  3. Choose Link CAD option
  4. Choose positioning as centre to centre.
  5. You can move the referenced point on CAD to the project base point or survey point of Revit.
  6. If the orientation in Revit is set as Project North, then rotate the CAD file, so that it is also in a project North orientation.
  7. In 3D view , there will be a difference in elevation of the linked CAD file and project basepoint and survey point. You can correct this by moving the CAD file to the elevation of the reference points so that they coincide.
  8. Go to manage Tab- coordinates – acquire coordinates—select the CAD file.
  9. Now the coordinates from the survey file will be obtained in the project.
  10. Unclip the survey point and move it to the project base point depending on your workflows.
  11. Adjust the elevation of the survey point too.

Steps in Revit (2018)

  1. All steps above
  2. Acquire coordinates
  3. It might look the same, but if you look at the properties of the survey point, the elevation Northing and Easting has the same values of the surveyed location.
  4. Also u will be able to view a geolocation of latitude and longitude.
  5. In location u can view GIS system information and even timezone.

REFERENCES:

https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2020/ENU/Revit-Model/files/GUID-EE95E55A-A600-49DB-B6F0-113C239B5F1E-htm.html

https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/simplecontent/content/revit-geo-reference-gis-coordinates-linked-cad-file.html

https://pro.arcgis.com/en/pro-app/help/data/revit/3d-georeferencing-revit-or-cad-data.htm

https://www.eagle.co.nz/sites/default/files/Aubrey%20Miller%20-%20Workflow%20for%20transforming%203D%20building%20models%20into%20spatially%20aware%20GIS%20dataR.pdf

https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2018/ENU/Revit-Model/files/GUID-E67ED082-2556-475B-84A7-4605329F612F-htm.html

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