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Saturday, March 19, 2011

Revit Quiz: When I Export a #Revit project with 2 Locations why does 0,0 vary in the DWG for each Location? - RT @revitclinic

Source: http://revitclinic.typepad.com/my_weblog/2011/03/revit-quiz-when-i-export-a-revit-project-with-2-locations-why-does-00-vary-in-the-dwg-for-each-locatio.html

by Ryan Duell
You have 2 Locations in your Revit project.  The first has a 0 degree rotation between True and Project North.  The second has a 25 degree rotation between True and Project North.  When you change coordinate systems in AutoCAD, and draw a line at 0,0,0, the point varies between each system.  Why is that?
Scroll down for the answer…

When the Survey Point and Project Base Point are at the same location [for example startup 0,0] and you apply an Angle to True North rotation to the Project Base Point, the Survey Point  rotates at the same point.  So the location doesn't change.
If the Project Base point was unclipped and moved, and then the Angle to True North is adjusted, you will see the Survey Point rotate around the Project Base Point.  This will create a different 0,0 point for this Location in AutoCAD.
Here is a simple video showing this [no sound]:
Video Example Part 1
If I export my Revit project with the following 2 Locations, 2 Coordinate Systems would be created in the DWG as follows:
Internal – 0,0 will be in default location
25 Deg Rot.  – 0,0 will match Internal since I rotated the project base point over the survey point
If I export a version of the Revit project where I rotated 45 degrees when the Project Base Point was in another location [thus moving the Survey Point around it] I would have the following:
Internal – 0,0 will be in default location
45 Deg Rot. – 0,0 will be rotated 45 degrees down to reflect the survey point moving
Here is video part 2 opening the exported files in AutoCAD for comparison [no sound]:
Video Example Part 2
Remember when you change the Angle to True North you are actually rotating a Project True North.


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