Use this method if you have started modelling, have a survey, and need to establish a project base point and direction of true north.
If you want to start modelling or have already started, but don't have a survey, and want to establish True North for correct shadows use SET TRUE NORTH.
If you are starting a new project from scratch and have a site survey showing true north use SET PROJECT BASE POINT by ROTATING PROJECT NORTH.
Important decisions that will have ramifications for the rest of the project life must be made before setting your Revit model up.
These decisions should be discussed with the project architect.
Changing these decisions once the project starts causes an enormous amount of confusion and work for the whole design team, including consultants, so it is important to get it right.
1. Select where the project base point is.
This will be used to coordinate all linked Revit & CAD files by the whole consultant team.
Ideally it should be a physical point identifiable on site (e.g. corner of a building), surveyor's bench mark or corner of a title boundary.
2. Identify which building face or boundary will align with the top of sheets (and your computer screen).
If you have started modeling this may have already been decided, but this is a good time to review that decision. Consider how the project will fit on sheets, not just for the early design stage, but also documentation when there will be many more sheets.
3. Work out what the R.L. of at least one of your floors will be.
The measurement system must be same as the survey. Usually AHD (Australian Height Datum), which is height above mean sea level, or GDA (Geocentric Datum of Australia) which is based on the centre of the earth rather than sea level.
4. Prepare the first Survey CAD file.
Open the survey CAD file. There is not a lot of point spending too much time cleaning it up, particularly if you expect future updates.
But you need to make sure there are features that clearly mark items 1 & 2 above.
For the base point the end point of a line is best. Make sure there are no other lines very close, or on top of, this line. If necessary draw your own line in the CAD file (e.g. could be the corner of title boundary).
NOTE: Title boundaries do not always meet at corners. Because surveyors do not measure to 12 decimal places rounding can cause there to be a gap at one corner. If using a boundary corner as base point double check to ensure the corner you have chosen does not have a gap. This is more likely to happen with non-orthogonal title boundaries.
For identifying coordinates make sure there is an identifiable point somewhere that notes the coordinates at that point. If you can not find one, make sure you in World UCS, then use the AutoCAD ID command (or similar Microstation command) to identify coordinates at the base point. Note down these coordinates (or write in the CAD file).
For identifying the building face or boundary that aligns with project north (item 2 above) make sure there is a single line (not a polyline) drawn in the right direction.
Check for other lines very close, or on top of, this line. Work out how you will identify this line in Revit (i.e. what layer is it on), or if necessary draw your own line in the CAD file.
For aligning True North make sure there is a single line (not a polyline) that goes north-south. (Surveys are usually orientated true north in World UCS). Often a north point will be adequate. Check for other lines very close, or on top of, this line. Work out how you will identify this line in Revit, or if necessary draw your own line in the CAD file.
Take note of the units in the CAD file (usually metres). Double check by measuring something, sometime surveys are drawn at a scale.
You need to know this when you link it into your Revit project.
Identify and take note of which layers are used for:
- title boundaries
- contours and/or TIN triangles
- text showing RLs
Once this CAD file has been placed in your Revit project and the coordinate system has been set up you won't need to do this again if you receive updated survey files.
Exit all but one instance of Revit.
(Having multiple instances of Revit with linked files open confuses Revit, and will confuse you. Changes will not necessarily propagate between files as you expect.)
Open your project file.
What you do next depends on whether you have changed the project elevation of your levels.
If your entry level (e.g. Ground or Level 1) is at project elevation 0.000 then:
Duplicate your entry level and call it Z_datum. Make it a working type. It will also be at project elevation 0.000.
Go to the floor plan view Z_datum.
Change the View Range so Top, Bottom & View Depth are all set to Unlimited, change Cut plane to be above your project's roof (e.g. 90000).
If not visible turn on Survey Point and Project Base Point via Visibility/Graphic Overrides > Model Categories > Site.
In this view make sure view parameter Orientation is set to Project North.
If you have changed the project level to match the AHD level (not recommended) then:
Create a new level at RL 0.000 called Z_datum. Make it a working type.
Go to the floor plan view Z_datum.
Change the View Range so Top, Bottom & View Depth are all set to Unlimited, change Cut plane to be above your project's roof (e.g. 90000).
If not visible turn on Survey Point and Project Base Point via Visibility/Graphic Overrides > Model Categories > Site.
In this view make sure view parameter Orientation is set to Project North.
Automatic Center to Center,
Import Units to match units in the CAD file,
tick Current View only. (if you want it in another view copy and paste it into that view later).
untick Straighten Lines.
(If the origin is more than 20 miles (32 km) away Revit will force it to link at Center to Center. You will receive a warning, accept it.)
NOTE: If lines in the CAD file are 'jittery' - they move about as you zoom in and out, the CAD extents are too large for Revit. To solve this first try opening the CAD file, do a ZOOM ALL. If it zooms a long way out there are elements a long way from the main drawing. Delete these elements and do a ZOOM ALL again. If all you see is the main drawing save the CAD file and reload it into Revit.
If there are no elements at extreme distances there are two methods to overcome jitter, both with their own problems:
Edit the CAD file by moving all elements so your base point point is at World UCS 0,0,0. (you will lose the connection between CAD coordinates and Easting and Westings. Also you will have to repeat this if you receive an updated CAD survey.)
Create a new CAD file, xref in the original survey CAD and place it so that your base point point is at World UCS 0,0,0. (you won't be able to identify CAD layers from within Revit).
Enable Thin Lines. Unpin the CAD survey.
Identify which line representing a building face or boundary in the CAD survey that will align with project north (see item 2 of BEFORE OPENING REVIT above).
Use Rotate command to rotate the CAD survey so the line identified above aligns with project north (i.e. up/down or left/right on your screen).
Then move the CAD survey so the base point (see item 1 of BEFORE OPENING REVIT above) aligns (as best as possible) with what has been modelled so far.
(For example if the base point is the corner of title boundaries move the CAD file so the distance from your model to the boundary is correct).
Pin the CAD survey.
If the CAD survey has title boundaries in it you can use those to create Property Boundary lines.
Identify which lines in the CAD file represent property boundaries you need (usually by the layer they are on).
Use the Property Boundary command with Pick lines to copy the CAD title boundaries.
Select the Survey Point (blue triangle with cross in it). You will see a paper clip icon next to it. Click on this icon (a red line will appear through it).
Move the Survey Point by dragging it to the base point in the CAD survey identified in item 1 of BEFORE OPENING REVIT above.
Leave the Survey Point unpinned (red line through it).
NOTE: Moving the Project Base Point (blue circle with cross in it) doesn't change the origin used for Origin to Origin when inserting files. Therefore there is NO point moving the Project Base Point.
Draw a Reference Plane along the line in the CAD survey that represents true north (usually part of the North point symbol). Name it "True North". Move it so its bottom end sits on the Project Base Point (blue circle with cross).
Draw a Reference Plane from Project Base Point (blue circle with cross) along project north boundary (i.e. up your screen).
Name it "Project North".Set view parameter Orientation to True North.
From menu: Manage > Position > Rotate True North. Rotate from "True North" reference plane to "Project North" reference plane.
(i.e. pick "True North" then "Project North").
Test if it worked by changing view parameter Orientation to Project North.
NOTE: If you have changed the project level to match the AHD level (not recommended) you can NOT use this method. Your RLs are now fixed and changing them will move the model.
AHD (Australian Height Datum) levels are the height above mean sea level. If you know what the AHD level of one of your Revit levels is meant to be you can set it to be that level.
Go to a floor plan view whose associated level is the level you want to change (e.g. Level 1, which you want it to be RL 98765).
Make sure there is a model object whose top plane aligns with this level - a floor is best. (Annotation objects like lines won't work).
From Manage tab, Project Location panel, Coordinates, Specify Coordinates at a Point command.
Pick somewhere on the model object, change Elevation to the AHD value in millimetres you want.
Leave values East/West and North/South and True North angle as they are. (they may be blank if you didn't pick a point)
NOTE: If you have changed the project level to match the AHD level (not recommended) you do not need to do this as your CAD file will already be at correct RLs .
If you have done Set SURVEY ELEVATION (Height) as described above then change the elevation of Z_datum to be survey elevation 0.000.
This will place the contours and/or TIN triangles at their correct RL. You can then create a Top of Surface from CAD contours or TIN triangles.
Go to an elevation view, find the appropriate level reference. Make sure the Level Reference's type parameter Elevation Base is set to Shared. The value should be the same as what you typed in above.
Check other levels. If they are wrong it could be because the Level Reference's type parameter Elevation Base is not set to Shared.
If the survey has absolute coordinate values you can set these in Revit. If you don't have them it doesn't matter, skip this part.
Identify a point on the CAD survey that has known Easting and Northing values (also refer item 4 of BEFORE OPENING REVIT above).
Write down values as you may need to zoom in so close you can't read them on your screen.
From Manage tab, Project Location panel, Coordinates, Specify Coordinates at a Point command.
Pick the point on the CAD survey (use Tab key to snap to a point) and type the values into East/West and North/South. Leave True North angle and Elevation as is.
Draw a Model Line starting at that point (you can't select a CAD import with Spot Coordinate command as it is only 2D).
From Annotation tab, place a Spot Coordinate tag on the CAD survey point. Choose a type that shows elevation. Make sure E & N values and RL match the survey's values. Test at other points (if possible).
Make sure no-one (including yourself) has any linked files open.
Select Coordinates > Publish Coordinates from menu and pick a linked file.
Repeat for other linked Revit and in-office CAD files.
Save your central file, you will be asked if you want to also save each linked file, say yes.
Once files have shared coordinates you can link them using Auto - By Shared Coordinates rather than going through the publish/acquire procedure.
Consultants use the same process, so will acquire your shared coordinates from the file you give them.
This means when you receive their file it will come in at the correct spot if you use Auto - By Shared Coordinates.
An full explanation of the differences between Project Base Point and Survey Point:
Project Base Point And Survey Point Explained.pdf
An alternative method using an AutoCAD file: