In this tutorial we will explore the techniques and tools used to successfully coordinate a Revit project to a survey or OS grid. This process is often neglected which will cost you dearly later on! The problem is that this is only done once at the start of a project so is easily forgotten. A primary consideration is preparing a CAD file so that it is suitable for import into Revit. See Step 1! Get this wrong and the whole process will fail.
Link to YouTube Tutorial : http://youtu.be/xlO7KF0vsS8
In a later tutorial I will outline the process of coordinating with Autodesk Civil 3D and a 3D TOPO but in this tutorial we will concentrate on a 2D survey, this could of course be in a variety of formats such as DWG, DGN or DXF.
1. The first step is to prepare your incoming CAD data for use within Revit. This will involve checking the UNITS of the CAD file (i.e. millimetres or metres), accuracy of the drawing and the layer configuration. If you have a very large survey then I would recommend using the WBLOCK command to select the relevant data and saving as a different name, this will clip a very large file. You will also need to check the extents of the file, if any data is outside your limits then delete (must not be greater than 20 Miles). At this point, freeze or turn off any layers that you do not want to be visible in Revit
2. It is advisable to clearly mark a primary agreed setting out point on the CAD file that can be seen in Revit. This should normally be on a grid intersection and agreed and used by all Revit Buildings and disciplines (Construction, Architecture, Structure & MEP). If you know the consultants, architects and contractors who you are working with try and set up a Revit coordination meeting before any major modelling goes ahead to agree a universal setting out point that all Revit Buildings and models will use.
You can also create a secondary SOP for verification purposes. This should include the Easting, Northing and a level as shown below. If the structure is fairly large then you can consider increasing the precision of the coordinates. This is particularly useful for rotational errors that may occur.
Save the CAD file.
3. You are now ready to import the CAD file into Revit Structure. Once the CAD file has been selected you will need to configure the various setting within the dialog box. In most cases you will want to preserve the colours. Set the Layers/Levels to Visible and this will import only the CAD data that is on. Make sure that the units are set to the survey units, i.e. if the original CAD drawing is in Metres set the Import to Metres. The positioning should always be set to Auto – Centre to Centre. This will place the centroid of the CAD Building directly into the centre of the Revit Building (Note that this must not exceed 20 miles).
4. You will now move the CAD file to the Revit datum (0,0,0) position. The Project Base point will need to be visible; in the visibility graphics dialog box check the Site Category and then check the Project Base Point sub category.
Once you have moved the survey your Building will look similar to the image below. Note that the project Base Point is now at the agreed setting out point (Some contractors may want to use the local agreed coordinate system on large sites for piling etc.)
You now set the Revit Site coordinates to match the CAD survey. Click the Manage Tab, Project Location, and Specify Coordinates at Point and select the Project Base Point. Enter the Easting’s, Northings and Elevation.
5. Save the Revit Building as the ‘Site File’. You will later insert your Revit Buildings into this file and acquire the coordinates.
6. You now prepare the Building file. Create a new Revit project with your active template and then make the Site Plan current view.
Using Visibility/Graphic command (VV) switch on the Project Base Point.
7. If you have a DWG with the grid and architectural features then import this into the current view using the same rules as when importing the site plan. Move the Building to the agreed setting out point (Grid Intersection). Add a Spot Coordinate to the project base point, this should read 0,0
8. Save the project as the Building File (e.g. Building A)
9. Open the Revit Site File and then import the Revit Building File by selecting the Insert Ribbon and then the Link Revit command as shown below.
The Linked Revit File will now appear in the centre of your site file. Move and rotate the file to the Project Base Point to match the setting out of the grid. If you are new to this procedure then be sure to watch the tutorial video.
10. You will now acquire the coordinates from the Site file and record these into the Building file. Select your linked Revit file and in the Properties Window click the Not Shared button as shown below.
Once the Not Shared button is clicked you will see the Share Coordinates dialog box. Use the first option which will publish the Shared coordinate system of our site file into the Building file.
11. Close the Site File and Open the Building File. You will see a dialog box asking if you want to save changes, click yes.
12. Open your Building file and return to the Site Plan. You should now see the correct coordinate system and if you change the Orientation from Project North to True North you will see the Building rotate to a True North position.
12. Because the Revit Building file is linked, if the Building file is moved within the Site file then this will be ‘pushed back’ to the Building file and all coordinates and levels will be updated.
Tips and Tricks
Don’t forget to change your Levels to Survey. This will ensure that your project levels are always synced to the Site. Any changes to the site will instantly update the Building files.
Don’t forget to watch the Tutorial Video, a lot to take in!