BIM 360 Blog

How to take off items in Navisworks Quantification

5th October 2013
Posted by Lee Mullin
So far we have talked about the rough workflow in Navisworks Quantification and building Catalogs in Navisworks Quantification, now we get to the fun part (at least for me), taking off objects. There are three types of takeoff,
  • Automated takeoff where properties are brought across from the model
  • Manual takeoff, where you will need add the properties yourself
  • Virtual takeoff where you takeoff an item that hasn’t been modelled
Automated Takeoff Let’s start with how to take off an object that is in the model, you’ll be able to add objects at Composite Object level (in the selection tree this has a box with a cross on), that has a GUID (a unique ID to identify it). So taking a sample Revit model, either exported NWC or imported RVT file, you will be able to change the Selection Resolution to First Object (under Select and Search in the Home tab), then follow one of these methods to take off the object to an item in your previously created catalog. In the Quantification Workbook find the relevant Item or group to add this selected item to, you can create a new item as part of this group if the item doesn’t yet exist. 1) Model Takeoff > Take off to Selected Item or New Item 2) Drag and Drop to Quantification panel with an item selected, this won’t work if you have a group selected. 1 3) Right click > Quantification > Take off to selected item or new item 2 As with most of the major features in Navisworks, the most effective way to run the process it to build up relevant Search Sets based on properties in the model, in this case this is important for the first run, these can then be reused between projects and keep up to date with changes in the model. Create the search sets for the level of granularity you want the takeoff to be run in, for example all steel beams, or all steel beams using a particular grade, or all steel beams using a particular grade on Level 2, or all steel beams of a certain thickness on Level 2. Then takeoff the objects using one the methods above. If you try to take off a model object that is an instance, or if the object does not contain a GUID or properties, an error message is displayed. Note. If you are using Searches, we recommend you take off objects initially using the Search set, this will take off all the objects in the search at that time, on subsequent passes this will take off objects multiple times if you blindly accept the warning. Use the hide takeoff feature to see what new items need taking off in subsequent passes. Manual Takeoff Sometimes you won’t get the necessary property in the model for example you want a property ‘Beam Height’ rather than just ‘Height’ or this is a file we have not yet created mappings to yet. Where a property is not immediately picked up, it is possible to add a new mapping to it, we have a guide to mapping properties if you want to have a go yourselves, otherwise Autodesk Consulting or your partner can provide services to build out a mapping to the products you use. Otherwise you can still add the properties manually. If the property you need is in the Properties Panel (normally under the Element tab for Revit, or Civil 3D tab for Civil 3D, etc), then you can right click, and copy the value, then paste it into the relevant cell, this will take in any formulas you have set up. For example you may want to manually add a ModelHeight as the ModelWidth and ModelLength are available but Height is listed as Unconnected Height, you then have a Volume formula of =ModelWidth*ModelLength*ModelHeight which takes the Width and Length you have automatically mapped, and the Height you have manually added to create a volume value. If the property is not available at all you may want to use the measure tools which have been revamped in Navisworks 2014 to get the value from the geometry. By taking a measurement (the cross indicates a corner, and you can zoom in by holding Enter and using the + and – to change your zoomed view), you can check the point to point values, an area, a perimeter, or a diameter to calculate a round area from, these can then be added to the relevant part of the takeoff. By using the Convert to Redline tool, then using the small camera button to the right of Virtual Takeoff, this will save a Viewpoint with that measurement for reference that will be attached to that taken off item. Virtual Takeoff Virtual takeoffs can also be created to represent items that have not yet been modelled but will need to be accounted for in the final takeoff, This may represent an annexed building, a missing beam or a surface that may need additional treatments or finishes. These un-modeled items can be key components of a project and need to be quantified along with the modelled object to get a “complete picture” of the items you will be including in your project. In addition to acting as a holding place you can attach views, markups, measurements, and comments, helping to communicate the virtual item in context with the rest of the model. To create a Virtual Takeoff, simply select the relevant catalogue item you want to create a virtual takeoff for, then select the Virtual Takeoff option, you can then manually add the dimensions you’ll need and create mark up and measurements using the review tools as we did earlier and save the viewpoint using the camera button. In our next post I’ll go through a verification and validation workflow that estimators will want to use when transitioning away from traditional takeoff methods. This should gain trust in the measurements from the model and help address issues immediately for incorrect figures.
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