Navisworks Takes Off
Autodesk® Navisworks® 2014 takes off model quantities and allows for revisions. In this article, we’ll delve into Navisworks catalogs and explore how to take off model quantities and how to take off items that are not modeled.
Quantification
The quantification tool is broken out into multiple panes. The Navigation pane shows items and the resources associated with them. The rollup pane gives header-level information and the takeoff pane gives item-level information.
Figure 1: Quantification module
You can think of items as assemblies composed of resources. Resources can be customized to calculate quantities in items. The takeoff pane enumerates the quantities of each object taken off in the item’s resources. The sum of the amounts is listed in the rollup pane.
Exploring Catalogs
There are two main catalogs: Resource catalog and Item Catalog. The Resource catalog should contain each item type you wish to take off. For example, if you are taking off a footing, you will want to take off concrete, rebar, and form work. This means you will need a resource for each.
It is recommended to create folders in the resource catalog for each type of resource. For example, create a folder for concrete, metals, and wood. In each folder create the respective resource.
When creating a resource you have the opportunity to modify the formulas used for calculation. Modify the formulas for each resource until they calculate to your specifications.
Once you have created resources, you can create your items. For footings, create an item and name it by footing type—for example, Footing F8. Right-click the item and select the items you wish to use. Hold ctrl down to select multiple items and select the Use in Item button. The resources are now associated with the item.
If you update a formula in the resource catalog, the change will propagate to each item that contains the resource. If you only want to change the resource in one item, you can modify the formula in the item catalog to change only the associated item.
Model Quantity Takeoff
Building information models vary in their diversity and complexity. Some models have astounding geometry; other models have poor geometry but are rich in data. When considering using Navisworks for model quantity takeoff, you are most interested in models that are rich in metadata.
Navisworks will only take off model geometry when the model has metadata associated with it. This is important to keep in mind when reviewing dwg files and other file types that may not have quantity data associated with them.
To take off model geometry, select the geometry you wish to take off. This can be accomplished in a variety of ways. A sustainable method would be to create a search set for model groups. For example, you might create a search set for footings, foundations, walls, doors, and so on. An alternative method that is often employed is the use of the Select Same tool, a great tool to use when taking off a similar object. For example, when taking off a particular footing, follow the steps listed below.
• Select the footing in the scene view
• Click the Select Same tool
• Select a common component—usually name or type is used
• Click the Model Takeoff button in the Quantification window
Figure 2: Select Same tool
Once the model is taken off, it appears in the rollup window and the quantification window. The geometry that was taken off will change in color in the scene view. You can toggle the visibility setting of items that have been taken off in the scene view by using the Hide Takeoff Show Takeoff tools. These tools make it easy to identify items that have not been taken off.
Following a workflow of using the Select Same tool to select similar groups of geometry, the Model Takeoff tool to associate geometry with a takeoff item, and the Hide Takeoff items, you will be able to quickly take off all the quantities in your model. These quantities can be exported to an XML or Excel file.
Model Revisions
It is the nature of design and construction to have item quantities that are updated during the design and construction cycles. The Quantification module in Navisworks allows you to identify the changes to the quantities that you have taken off when a new version of the model is analyzed.
An item can be updated by a new model quantity, a deletion in the new model version, or by a change in the formula of a resource. Each change will be listed in the status column of the takeoff pane. If there is new geometry in a revision of the model, it will have to be associated with an item for quantity calculations. You can detect new items by selecting the Hide Takeoff tool in the quantification window.
Figure 3: Item status
You can review the changes to the quantities when there is an override or change by hovering your mouse over the affected cell. A fly out window will appear and display the old and new values of the quantities. You can then accept or reject the change. You can accept all the changes at once by selecting multiple rows in the takeoff pane and clicking the Update Selected by the Model. This will update your quantities to the new values taken off in the model revision. You could also reject all the changes by selecting the rows in the takeoff pane you wish to reject and selecting Remove Override from Selected. Using these methods you can manage the changes to the quantities during model revisions.
Model Considerations
When performing model takeoffs, remember to ensure you are capturing the geometry you are interested in and not any duplicate geometry. It is not rare to find walls stacked on walls, walls used for geometry not meant for walls, and other model cheats. It is important to understand the model you have been given in order to properly obtain quantities.
The model review process is key to ensuring you take off each element properly and ignore superfluous elements. It is also important to understand the nature of the elements you are taking off. For example, if you are taking off wall surface area from a Revit model, you are actually taking off net surface area. This means that any voids created by windows, doors, and other families will not be included in the surface area of the wall.
Working with models can enhance your ability to quickly and accurately take off a project. A workflow can be established that allows you to review changes to geometry and persist quantity changes for pricing.
