Revit models the ground using the Toposurface element, a plane made up of multiple points.
Unless the site is extremely simple it is a tedious task to create a Toposurface by manually placing points. A better method is to create it from data provided by others.
But keep in mind a Toposurface will only be as accurate as the data it is made from. Surveyors only make selected measurements, there is rarely sufficient measurements to create a truly accurate Toposurface. However if measurements critical to the project have been included the Toposurface is still useful as it will be accurate where those measurements have been taken. The secret is to make it accurate where needed, and looking "about" right where it is not.
NOTE: currently (2015) you can't create a usable Toposurface from a Point Cloud file. A point cloud can be imported into Revit, but it is not usable as a terrain.
FROM A CAD FILE
Revit can make a Toposurface from CAD files containing a 3D triangular mesh, or containing contour lines that have a Z value (i.e. contours are drawn at their RL).
The process in Revit is very simple, the secret is to prepare the CAD file.
PREPARE SURVEYOR'S CAD FILE
From the project's Surveyor obtain a CAD file containing 3D contours or a triangular mesh (called a TIN - triangulated irregular network).
A TIN is probably going to be more accurate.
Open the Surveyor's CAD file.
Save As under a different name.
Optional, but desirable: delete everything except either the triangles or contours from the CAD file (keep level text so you can check your Toposurface). Purge All.
Identify where the Revit Project Base point or Survey point (depending on which one is being used) is in the file (e.g. corner of title boundary, bench mark etc).
Draw a line from that point to the CAD file's insertion point (BASE in AutoCAD, usually 0,0,0).
Move everything (check no layers are off or frozen) from the CAD files insertion point to Revit's base point (Move from End of line to other End of line).
Identify the layers or levels the triangles or contours are on. You might want to rename or change the layers they are on if the CAD file setup is confusing.
Note the Units of the file (AutoCAD UNITS).
Save (don't overwrite the original Surveyor's file).
IN REVIT
Go to a SITE view (or a view with a cut plane higher than the site)
Link the CAD file prepared above.
- Auto - Origin to Origin.
- Select appropriate Import units noted above.
- Untick Current view only.
- Untick Correct lines that are slightly off axis.
Massing & Site > Toposurface > Create from Import > Select Import Instance.
- select the CAD file.
Toposurface will be created (which may take a while).
Green tick to finish.
Select the Toposurface and change it's Phase property to Existing, (as it is part of existing conditions, not new construction).
Use Annotate > Spot Elevation to drop elevation references on to the Toposurface to check if it is accurate.
If the Toposurface worked OK select the CAD file, unpin it, delete it.
ALTERNATIVE SOURCES OF CAD FILES
If a Surveyor has yet to be appointed you can create your own CAD file.
CONTOURS
If you have a flat CAD file containing contours make a copy of the file.
Move the contours to their correct RL (3DMOVE in AutoCAD).
If you have survey drawing scan it, if you have a PDF export as image.
Import the image into Revit, resize so it is to scale.
Trace the contours with Model lines at the contour's correct RL.
Export the view as a CAD file.
MESH (TIN)
If you have a model of the terrain in another software (Sketchup, Rhino, 3DMax) export it as a 3D DWG file.
You can also get very rough terrain information from Google Earth.
For one method see TIPS & TRICKS > SITE > CREATE TOPOSURFACE FROM SKETCHUP.
FROM A POINTS FILE
A Points File is a text file containing a list of X, Y, Z coordinates. (Not to be confused with a Point Cloud file which contains millions of points).
The Surveyor may be able to provide a points file (or a file that can be turned into a points file), but if they have already provided a triangular mesh (TIN) file the points file won't be any more accurate or comprehensive.
Point files can be created from meshes using scripts (e.g. a DOS batch file that extracts points from a DXF file), or some software can export them (e.g. Rhino can export points as a point file). Again if a mesh is available there is probably little point.
FROM CIVIL 3D (OR SIMILAR)
In 2015 AutoDesk made the Site Designer Add-in available on their subscription web site.
This add-in can use LandXML files to create a Toposurface. This is an open format, used by Civil 3D, but also some other civil engineering software.
If your Civil engineer is using 3D software it is worth asking them for a LandXML file.