Thursday, 3 April 2008

CAD Surveys and Your Revit Project

This text was posted at AUGI by David Conant (Autodesk Revit Product Designer) in February this year. It is very important information.

This method should ALWAYS be followed. It is critical to follow when the survey coordinates of your building site have large values (> 2 miles/3km from site 0,0):

ALWAYS locate sites underneath buildings. Revit buildings like to stay near home and be oriented to project north. Sites can wander about and talk to the buildings later. DON'T try to pan your view 40 km northeast of 0,0 and try to build your building model there because your site coordinates have a remote origin. This will work in AutoCAD but in Revit you will be very unhappy.

NEVER import or link a site with large coordinate values Origin to Origin! This may seem correct based on AutoCAD experience, but here too you will be very unhappy in Revit. You will get the correct origin later in the process.
  • Build your revit model at or near the position of the elevation marks in the default template with the building oriented orthagonal to your desired printing frame. i.e. use a Project North not True North for your working environment.

For one building on a site:

  • Link in a site model or site dwg.
  • Move and Rotate the SITE so that it is located correctly relative to the building.
  • Acquire the site's coordinates. Now, the site's origin will be the origin of your shared coordinates. The site's Y axis will be True North. The site coordinate values can be arbitrarily large without disturbing Revit's internal calculations.
  • You can later open the site model and link in the building using shared location and it will land in the exact position.

For multiple buildings on a site:

  • Create a Site project, link in a site dwg, placing the center of the building site near the center of the default view.
  • Acquire coordinates from the site.
  • Build any site elements, topos, etc.
  • Link in building rvts. Move and rotate them so that they are correctly located on the site.
  • Publish coordinates to the rvts. Now all models will have the same Shared origin and True North orientations.
  • You can now link the site into any of the buildings (the other buildings can be linked in as well) using shared location and it will be in the exact location.

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