Friday, 6 April 2012

Revit shared coordinates

Workflow for getting Autocad based product drawings and Revit models at the same coordinates in Navisworks. 

If you want to use Project North and True North you better read a later post of me:http://danielgijsbers.blogspot.nl/2012/09/project-north-thrue-north-with-shared.html

Recently I ran into a project where 3 teams are working in Revit: RST, RAC and MEP. You would think that they should not have any problem with getting the models lined up in Navisworks.

We wanted to do clash detection in Navisworks so we exported the models to nwc. Somehow somewhere something must have gone wrong. In Revit it looked fine but not in Navisworks.

(Navisworks 2013 will be able to read rvt files and it's linked files!!!) 

I have already written tips for exchanging information between Revit and Civil 3D on my civil2revit.blogspot.com I'll add a workflow I like to use that so far seems to give the best results and gives you the most control!

We have a dwg of a site that has been drawn accordingly to a coordinate system. Since I am dutch we use the rd-system. Revit has a 30 km boundary around it's origin where you have to put your model. This means you can't model anything in Revit if it's located anywhere in The Netherlands. Basically what you will be doing is moving the dwg with the location under the revit origin. 

From experience I know that Revit 2012 has some rounding issues which I haven't been able to pinpoint yet. For safety reasons I have a trick to bypass that issue.

Steps: Autocad
  1. open the dwg from the site
  2. choose a easily recognizable point as a project basepoint
  3. use the ID command in autocad to find it's xyz values
  4. create a symbol, I prefere a circle with a cross, and place that ontop of the choosen point
  5. move the symbol to the nearest round value (important because of rounding in Revit)
  6. This location is going to be the project base point
  7. copy the ID value of this point and paste it into notepath
  8. Save the drawing
Steps: notepath
  1. Be aware most coordinate system are in meters and Revit models tend to  be build in mm.
  2. This means you need to move the comma 3 spots to the right
Steps: Revit
  1. Open your level that has a Z value of zero
  2. Goto visibility and graphics
  3. Goto the site category, expand and turn on survey point and basepoint
  4. Select the project base point (the circle)
  5. Copy the X value from notepath into the E/W
  6. Copy the Y value from notepath into the N/S
Do not paste these values into your instance property window, you will get an error. If you paste them into the on screen thing it will accept those values.

Be aware you survey point will move away from your project base point. The project base point is still located on the Revit origin!

If you take a look at your survey point you should see that it's values are all zero. Your autocad origin (0,0) will be lined up with your Revit survey point.

Steps: Revit
  1. Goto Insert --> link CAD
  2. Choose the dwg with the site information
  3. Set Import units to the meters (assuming it has been drawn in meters)
  4. Set positioning to by shared coordinates
  5. press okay and you will get the next message
This is actually good because this should import the dwg origin on top of your survey point. This should also have the effect that the project base point marker you created in Autocad lands ontop of your project base point set in Revit.

Steps: Revit
  1. Goto visibility and graphics and turn of the survey point this will enable you to use zoom extends again
  2. draw two model lines in this view on top of Autocad lines
  3. Save the revit file and make an export the nwc
  4. Make sure that within the Navisworks export settings you set the units to feet... (yes really!!!)
Steps: Navisworks
  1. Attach the dwg (the one you linked earlier into Revit)
  2. Attach the nwc from Revit
  3. take a look at the lines you drew in Revit and whether they line up with the Autocad lines. If they do you are good to go!
  4. if you select the revit nwc file and right click it and go to units and transform you should get a dialog box with coordinates that are the same as the coordinates of the project base point in Navisworks. (nice to check) 
  5. If they don't check the steps and all the file and unit settings and adjust them accordingly where needed. If you still have problems contact me.

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