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Monday, May 25, 2015

Revit Tip - Controlling Your Levels: Project Base Point and Survey Point...

Here's the scenario.  You have a topographic survey completed in CAD by the surveyor.  Its a good file and you are able to import the CAD file and create Revit topography from the survey.  Nice!

Now, you want to model your building.  When you enter one of your elevation views you realize the topographic map is at 29'-0" and your Level 1 is at 0'-0".  Hmmm....  You want to model your building at the correct elevation (29'-0") but you want your wall sections, elevations, and details to read 0'-0" on your documents. Keep reading to find out how you can control what your Levels will show...

Thankfully, Revit gives us an option to control two different origins (for lack of a better word).  The two origins are:

Project Base Point:

Survey  Point:

You have probably come across these two points and not even realized it.  In fact, the default template has them overlapping in your site plan:

Does anyone recognize the symbol above?  That is actually the survey point and project base point overlapping one another.

I will restate the Autodesk Help page for a quick explanation on each point (because it is written very well):

Every project has a project base point  and a survey point , although they might not be visible in all views, because of visibility settings and view clippings. They cannot be deleted.
The project base point defines the origin (0,0,0) of the project coordinate system. It also can be used to position the building on the site and for locating the design elements of a building during construction. Spot coordinates and spot elevations that reference the project coordinate system are displayed relative to this point.
The survey point represents a known point in the physical world, such as a geodetic survey marker. The survey point is used to correctly orient the building geometry in another coordinate system, such as the coordinate system used in a civil engineering application." (Autodesk Help, 2014)

Following this definition and the example above what do you believe should be the Project Base Point and Survey Point?  Well, we want the project base point to be 0'-0" at 29'-0" "physical world" elevation.

Example 1: New Project

I typically approach this problem by leaving the Survey Point where it is (our real "physical" world origin) and moving the Project Base point up to the finished floor elevation (29'-0" in our example).

To move the point simply enter an elevation or section view, hit the light bulb to toggle hidden elements and you will see the two points.  Tab select the project base point and use the move command.

Click image to enlarge.
In the image above you can see the survey point on the bottom and the project base point even with Level 1.  Note that the Level 1 states 0'-0" yet it is at an absolute elevation of 29'-0" thanks to the Survey Point.  How can you double check this?  

Simply click the level in a section or elevation view, click "Edit Type", click "Duplicate" and rename your Level family to include "Survey" somewhere in it.  Now, where is says "Elevation Base Point" change it to "Survey Point".
Now, when you click Okay you will notice the level will dsiplay the elevation based on the survey point (29'-0"):

I mention that this example is for new projects because when you move the project base point of an existing project it opens up the possibility of ruining many views, sheets, sections, details, etc... It may work but it is a chance I am not willing to take.

Example 2: Existing Project

So what do you do if you are in an existing project and the project base point and survey point have both been moved to 29'-0" or at 0'-0" and you want it at 29'-0"?  Simple, instead of moving the Project Point up you can move the survey point down.  The nice thing about moving a survey point is no views will be ruined (the project stays in place).

BIM After Dark - Volume 2: Production

If you liked this tutorial you will definitely like Volume 2 of the BIM After Dark series.  Volume 2 demystifies the construction documentation process.  The full length videos show you how to create a set of construction documents with Revit faster than ever before.  In addition, it is packed full of sample files, templates, and goodies.